Succulent (Latin: succos = juice, sap) plants from more than 60 families and 300 genera have evolved special water-storage tissues in thickened or swollen leaves, stems or roots as an adaptation to arid environments. By making the most of scarce available moisture, succulents can survive in habitats that are far too dry for most other plants.
 
Leaf Succulents: Leaves are almost entirely composed of water storage cells covered by a thin layer of photosynthetic tissue.
Examples: Aloe, Haworthia, Lithops, Sempervivum.

Stem Succulents: Fleshy stems contain water storage cells overlaid by photosynthetic tissue. Leaves are almost or entirely absent, reducing surface area to prevent evaporative loss of water.
Examples: most cacti, Euphorbia obesa, Stapelia.

Root Succulents: Swollen fleshy roots store water underground away from the heat of the sun and hungry animals. Stems and leaves are often deciduous and shed during prolonged dry seasons.
Examples: Calibanus hookeri, Fockea edulis, Pterocactus kunzei, Peniocereus striatus.

Combinations of the above types may occur where more than one organ is used to store water. Some Caudiciform Succulents store water in both roots and swollen stems and may have deciduous or long-lived fleshy leaves.
Examples: Ceraria pygmaea,Tylecodon paniculata, Cyphostemma juttae.

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Aloe,

Haworthia,

Lithops,

 Lithops Optica

Sempervivum

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Euphorbia obesa

Stapelia with flower bud(before)

Stapelia flower bloomed (after)

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Calibanus hookeri

Aloe plicatilis

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General care

Pots and containers
 
Two types of pots are available, clay or plastic. Both types of pot are used successfully by growers, mainly as a matter of personal preference. Plastic pots are lighter, cheaper, require less watering and are easy to keep clean. Clay pots can provide stability for tall plants and can help to mitigate the effects of over-watering, but their accumulated weight requires strong staging.

Many cacti and succulents have fibrous roots and do not require or use the full depth of a standard pot, and half pots or pans are more suitable. Putting a shallow rooted specimen in a deep pot is counter-productive as the soil below the reach of the roots will stay wet for prolonged periods after watering and may become stagnant. Those species which have tuberous or tap toots may require more depth and will probably grow better in a standard pot or even a "long tom" if you can find one. All pots of whatever type chosen, should have drainage holes and the bottom should be lined with several pieces of broken clay pots or large clean gravel.

Bonsai pots can look very effective with caudiciform plants where the caudex (a swollen root or lower stem) is raised up above the compost. Finally, some cacti and succulents are native to limestone areas and often seen there growing in cracks in limestone boulders. Such plants are suitable for planting in a block of tufa and can look very effective as an alternative to alpines.

Soil Mixtures
 
Many different types are available commercially, ranging from John Innes soil based composts to peat based and recycled garden composts. Add horticultural grade sand and grit to make the mixture porous; the final compost contains between 30% and 70% grit. You may have to experiment a little to find the best proportions of compost, sharp sand and grit for your growing conditions and using locally available materials.

Peat based composts appear to encourage root mealy bug compared with soil based compost, and many growers feel that Lithops (living stones) grow atypically in peat-based media. I have personally moved away from growing in peat based compost in favour of soil-based mixture (see opposite). Coir fibre is becoming a fashionable alternative to peat, but is said to break down too quickly for use with slow-growing plants like cacti.

Some species e.g. Echevierias hate lime and are probably suited to a peat-based compost. Others e.g. Ariocarpus fissuratus, Echinocactus horizothalonius, Escobaria tuberculosa always seems to grow on limestone in their habitat and may appreciate a proportion of ground limestone or dolomite of lime in their growing medium. Still other plants e.g. Geohintonias are noted for growing on nearly pure gypsum cliffs.

Ground limestone is calcium carbonate with a mild alkaline reaction neutralising soil acids.

Dolomite of lime is a mixture of calcium and magnesium carbonates with a mild alkaline reaction.

Gypsum is calcium sulphate, neither acidic nor basic.

Garden Lime is calcium hydroxide and has too strong an alkaline raction for use in potting mixtures.

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Repotting a prickly customer
 
Ideally, plants should be re-potted every year to provide fresh compost and room to grow. This is also an ideal time to inspect the roots for diseases such as root mealy bug.

A good way of handling spiny cacti during repotting without breaking the spines is to wrap a roll of newspaper or paper towel round the sides of the plant. This may be kept in place if required by elastic bands or a wire twist tie. If the spines become entangled, wetting the paper will make it easier to remove, and small bits can be taken off the spines with tweezers. 'Old hands' often handle plants with bare hands during repotting by distributing the weight on the hands between as many spines as possible. However, this is not recommended with Opuntia Sp. as the fine spines (glochids) will break off and become embedded in the skin, or with Mammillaria species with 'fish-hook' spines that tend to catch in the skin.

To re-pot, invert the plant and tap the rim of the pot against the bench or with a piece of wood to loosen the pot from the compost. Inserting a piece of cane into the hole in the pot may help this process, but beware of damaging plants with fleshy or tuberous roots. If the plant is in a plastic or other flexible pot, squeezing the pot gently may help to loosen the root ball. As a last resort, it is better to break the pot to free a compacted root ball rather than damage the plant.

Remove the pot and clear away the old compost from the roots, keeping an eye out for pests. Use a thin stick or plant label to tease out the roots and remove old soil. If you see white fluffy patches in the soil and tiny insects, similar in shape to woodlice, but about 2 mm long these are root mealy bugs. If you find any pests, remove or wash off as much soil as possible, and soak in systemic insecticide, preferably one containing dimethoate.

Repot the plant into a new pot, which should be a little larger than the old one (perhaps 1 cm extra all round) if the plant has grown to fit its old pot. Replace fairly dry new compost around the roots and allow the plant to rest for about two weeks before watering to allow broken roots to heal.

Handling Euphorbias
 
The Euphorbiaceae comprise a fascinating group of succulent and non-succulent plants, with a wide range of growth forms and sizes, and are well worth growing. However, the milky latex characteristic of plants in this group is very poisonous and should be treated with respect. Euphorbia latex should never be allowed to come into contact with the eyes and any contamination should be washed off the skin immediately. It is a good idea to make a habit of washing one's hands immediately after handling or re-potting any Euphorbia species.

Light . . . . . . more about light and lighting
 
Most cacti and succulents need as much light as possible, and a south or south-east facing windowsill, conservatory, cold-frame or greenhouse is ideal. The type of plant that can be grown in these different locations is mainly limited by the minimum winter temperature that is likely to be reached. Lots of sunshine is essential to prevent plants from becoming "drawn" and to promote flowering. Although cacti often grow naturally in intense sunlight, they can become adapted to the lower light intensities in e.g. an English climate. Therefore, beware of scorching during the first sunny days of Spring after a long, dark winter. Newly-aquired plants or those grown under shading or low down on the greenhouse staging should be adapted to full sunlight over a few days.

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fertiliser (Cactigrow or balanced Chempack) should be added to each watering throughout the growing period. Rainwater barrels can be fed from house or green-house roofs.

To stop mosquitos and other insect larvae from breeding in your rain water barrel put a few drops of olive oil or other vegetable oil on to the top of the water. The oil spreads out and forms a film on the top of the water that stops the mosquito larvae from breathing air through the water surface. Renew the oil every week through the summer. Light mineral oils also work, but are less desirable contaminants.

Clean water can also be obtained from ice forming in refrigerators and freezers and from condensation from air conditioning units. If you are desperate, a simple solar still can produce several litres of water per day in a sunny climate. There are lots of resources on the internet for build-your-own solar still designs, but here is a typical design. 

Water from reverse osmosis desalination systems should also be suitable for use, but many domestic water softeners are based on ion exchange resins that simply substitute sodium ions for calcium.

Water treated in this way is unsuitable for watering plants as the substituted salts will accumulate.

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Taking cuttings is a fast way to produce new plants which are genetically identical to the original specimen. As there is no genetic diversity among plants propagated from cuttings or by division, any desirable traits are preserved, but any faults such as susceptibility to disease are faithfully reproduced too. In species which are self sterile, it will not be possible to raise seed by crossing two individuals which have been propagated vegetatively from the same clone.

Many species of succulent plant can be propagated from pieces cut from the stem of the plant with a sharp knife. Knives and other cutting tools used for propagation should always be sterilised by dipping in methylated spirit.

The best place to cut is just below a stem joint, or where a leaf or bud joins the stem, taking care to remove cuttings so as to not spoil the plant's shape. It is usually best to try to arrange for the cutting to have at least one more stem joint higher up. Ceropegia cuttings work well if taken as pieces with two pairs of leaves. Any leaves should be removed from the bottom stem joint, but it is counter-productive to rub off any buds in leaf nodes. The cutting should be potted up in a heat-sterilised gritty potting medium, pure sharp sand, fine grit or vermiculite. In some cases, cuttings can be potted up immediately after cutting, but I usually allow the cut end to dry for a day or two to let the damaged tissues to seal, reducing the chance of fungal attack. You may want to experiment with potting up cuttings both ways. It may help to dip the cut end in some hormone rooting powder, particularly as the powder also usually contains a fungicide.

A single leaf, carefully detached from many succulents is often sufficient to start a new plant, and is the preferred method for propagating e.g., Adromischus, Crassulas Echeveria, many Kalanchoes, Sansevieria and many epiphytic cacti. Gasterias may be propagated from a piece of a leaf. The leaf is allowed to dry for a few days so that the tissues seal and callus over at the base and is then placed against the edge of the plant pot with the stem end touching the potting medium. I find that this is better than burying the bottom end of the leaf as it is less likely to rot. After some time, roots will be seen to form, followed by small leaves as the new plant starts to develop.

Cuttings are best taken at the beginning of the growing season, usually in the Spring except for those plants that grow during the Autumn or Winter. The cuttings should be kept in a well ventilated bright place at about 20^oC, but not exposed to direct sunlight which places the cuttings under too much stress. It is a good idea to keep cuttings in an propagator with a top to retain humidity until they have become established. Alternatively, the pot can be placed inside an inflated polythene bag or the top half of a clear plastic bottle can be placed over a suitably sized pot as a make-shift propagator. The cuttings should be watered sparingly until some new growth is seen, which is usually an indication the some roots have developed.

Division

Many species of succulent plant form mats or clumps or thick tuberous roots and may be propagated by division. The plant is removed from its pot and as much of the soil as possible removed. The method of division then depends on the growth habit of the plant.

In other cases a thick tuberous branching root will be revealed and this can be divided with a clean knife into two or more pieces. Each piece should have growing points and vigorous roots. This sort of division is best carried out while the plant is dormant and dry, or it may be weakened by excessive bleeding of sap. Cut surfaces can be dusted with a fungicide such as Benlate or flowers of sulphur and allowed to dry for a few days for the tissues to seal and callus over. Each piece can then be potted up separately in a gritty potting compost and watered very sparingly until some new growth indicates production of new roots.

Offsets

Many species of succulent plants and cacti produce small plants at the base of the parent plant. These offsets can usually be easily pulled or cut off the main plant, allowed to dry for a few days and potted up individually. The main plant often benefits from removal of offsets which can divert energy from the main stem, and removal of offsets may be essential to the production of a large solitary specimen.

Other species produce minature plants on the edges of leaves, flower stems or flower heads, and these can also be removed and potted up.

Some succulent plants (e.g. mat-forming Asclepiads (left), Crassulaceae, multiheaded cacti) will disintegrate to a handful of cuttings as soon as removed from their pot, and good pieces with roots can be selected and potted up individually. If the goal is to raise a large specimen of this type of plant, either repotting must be very gentle or the cutting started in the desired final pot size.

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Grafting is a method of providing a delicate, cristate or monstrous cultivar with a hardy, vigorous rootstock. A variety of brightly coloured, but photosynthetically incompetent cactus cultivars, propagated by grafting, are widely available in the horticultural trade. Grafting is the only way of ensuring the survival and propagating these natural sports. Several grafting configurations are used, depending on the material to be used. Strict attention to hygiene is essential and cutting implements should be sterilised by dipping in methylated spirits.

Grafting Stock: In all cases the stock must be compatible with the graft to prevent rejection, which usually means the same genus or at least the same family. Suitable grafting stock includes:
For Cactaceae -- Echinopsis, Pereskiopsis, Trichocereus
For Asclepiadaceae -- Ceropegia tubers e.g. C. woodii.
For Portulaca Group -- Portulacaria afra

Flat Grafts are probably the simplest system for a beginner to attempt, and suitable for plants with fleshy stems such as cacti. The stock is first cut flat with a single clean cut with a sterile scalpel balde, razor blade or very sharp knife at a suitable height, usually above soil level.
The material to be grafted (scion) is then cut cleanly across and the cut surface placed on top of the cut stock in such a way that at least part of the vascular elements on both pieces are in contact. The graft is held in place with an elastic band which goes under the bottom of the pot at its other end.

Side Grafting is a variant of flat grafting used for relatively thin material in which the stock and scion are both cut at an angle to increase the area of cut stem and increase the chance of the vascular elements making contact.

Split Grafting is another method used for thin material, in which the end of the scion is cut into a wedge shape and inserted into a "V" shaped incision in the stock. The stock is then bound tightly with cotton to hold the two parts together.

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From time to time most collections of cacti and succulents develop problems, related to either pests and diseases or to incorrect cultural conditions. If well cared for, succulent plants should grow well and remain healthy, but this may not be easy when growing plants in a climate which is different from that in their native

Pests and diseases strike large collections in greenhouses and small windowsill collections indiscriminately, irrespective of the experience of the grower. However, a few precautions can reduce the frequency with which the problem occurs. Most pests can be controlled by appropriate treatments, although it is probably fair to say that these problems are never really eliminated from large collections.

A number of pests, diseases and cultural problems are described below with some ideas for control measures. Whatever you use, read and carefully follow the instructions supplied with the product and avoid personal contact with insecticides and other chemicals.

Please remember that all insecticides, fungicides and some other horticultural chemicals are very toxic to people, and handle with extreme caution - rubber gloves, face mask and goggles are advisable.

When new plants are aquired, from whatever source, it is a good idea to keep them separate from the rest of the collection for a few weeks so that obvious pests can be spotted. This allows time for eggs of pests to hatch and the progeny dealt with. A good way to do this is to maintain a "quarantine" window ledge separate from other plants. Many growers repot newly aquired plants into their favourite growing medium, and this is a good occasion to examine the general condition of the roots and check for pests such as root mealy bugs.
It may seem over-cautious, but many people like to treat their new plant with systemic insecticide while re-potting. This doubtless helps to avoid introduction of new pests into the collection. Repotting with "sterilised" compost which has been heated sufficiently to kill insects, larvae and eggs is a good idea.

mealy bugs for their honeydew secretions and may help to spread them through the collection.

Also watch how well individual plants are growing. Poor growth, a sudden change in condition or a limp plant which fails to take up water can be a warning sign of damaged roots caused by e.g. root mealy bugs, vine weevil, or roots rotting as a result of over-watering.

Hygiene
Cleanliness in the greenhouse is an important measure in preventing outbreaks of pests and diseases. Always remove dead leaves and flowers as soon as possible. Leaf litter provides an ideal hiding place for pests. If wet by watering, dead plant material is a breeding ground for fungi and production of their spores. Tidy up debris in the green house left from re-potting and propagation. Treatment of the ground under the staging, walkways and areas of paving with a disinfectant solution e.g. Jeyes Fluid is a smelly but effective traditional way of discouraging pests and diseases.

Pests of succulent plants

General comments on pest control measures
Many common pests can be controlled by use of systemic insecticides, contact insecticides, insecticidal soaps and, in some cases, natural predators. Systemic insecticides are very effective as they are absorbed by the plant, making its sap poisonous to the pests. However, they are also toxic to people and absorbed through the skin in the same way. Dimethoate is an effective ingredient of a systemic insecticide if you can find it, but unfortunately it has generally been withdrawn from the market, presumably because of worries about potential harm to people. Plants can be watered with a systemic insecticide a few times during the growing season as a preventative measure.

Contact insecticides such as Malathion can also be effective, but only at the time of application and all parts of the plant must be covered. Unfortunately, Malathion is toxic to Crassulaceae and some other succulents.
A range of insecticidal soaps are also available, and some people swear by spraying with diluted washing-up liquid (a few drops in a litre), which at least is fairly harmless.

It is worth noting that repeated use of insecticides can select for resistant insects among any survivors (evolution in action !). It is not yet clear whether resistance will develop to the new insecticidal soaps. This can be avoided by ensuring tha  [ send green star]

Mealy bugs
A very common pest of cacti and succulents, and potentially a huge topic ! There are many species of mealy bugs, but these insects are all small and hard to identify by amateur growers. Their host-plant range and individual sensitivity to control measures are poorly characterised anyway. There are probably several species of mealy bug going around collections in the UK and elsewhere. From time to time one certainly sees mealy bugs which "look different".

The insects are small and grey or light brown and so difficult to see among the spines of cacti. Their general appearance is reminiscent of tiny woodlice about 2-3 mm long. A squashed mealy bug often leaves a characteristic red stain: the cochineal insect, from which a food colourant is made, is a type of mealy bug. Recently, a species that leaves a green stain has appeared in the UK. Mealy bugs often accumulate to feed on the tender tissues at or near the growing point. Very often, when nesting, they hide around the base of succulent plants, just below soil level or under the old dried leaves of Mesembs such as Lithops.

The first sign of a problem is often small balls of white fluff on the plant, on cactus spines or around the base or under the rim of pots. These are actually where the females are nesting up inside the white fluff and producing young, which may be either born live or produced from eggs. There may also be some sugary honeydew produced by feeding mealy bugs, which can encourage black mould. Ants "farm" mealy bugs for their honeydew secretions and may help to spread them through the collection, so it is a good idea to discourage any invading ants even though they are not intrinsically harmful to the plants.

Control of mealy bugs: If there are only numbers of mealy bugs to be dealt with, dabbing a little methylated spirit (industrial alcohol, denatured alcohol) will kill them. Some people also spray their plants with methylated spirit diluted at least 1:3 with water. If you try this, remember that the fumes are potentially toxic and flammable and the liquid could harm the epidermis of delicate plants.

For large or widespread infestations, use regular applications (weekly for several weeks) of insecticidal sprays (read the label to find pests controlled, use and precautions). Wash off as many of the mealy bugs as possible with a high pressure water jet from a sprayer, and treat the plant with a contact insecticide such as malathion (not for Crassulaceae) or a systemic insecticide containing dimethoate, taking precautions to keep the insecticide off your skin and avoiding inhaling the spray. Adding a drop of washing-up liquid may help the insecticide to wet waxy surfaces and penetrate into all crevices. A single application will often not be sufficient to eliminate all the insects and their young. In a bad case, total immersion of the plant in a bucket of insecticide with a couple of drops of washing-up liquid to help wetting of the soil, will get the majority of the mealy bugs including root mealy bugs. The plant will need to be carefully dried out after a soaking and is at risk of rotting where damage from mealy bugs has occured below soil level, so although effective, this can be a "kill or cure" method.

Some fumigant smoke cones are also effective against mealy bugs, and have the advantage of being a dry treatment, but require repeated use to be really effective. Give the cone a good shake before igniting to reduce the risk of poor burning, place on a non-flammable surface and retire promptly after lighting the blue touch-paper fuse, before smoke emission begins. I like to do a preventative fumigation in the Spring and Autumn when it is too cold to spray or water the plants with systemic insecticide.

Biological control of mealy bugs: Introduce the predator Cryptolaemus montrouzeri, which requires temperatures of at least 70^oF (21^oC). It is difficult to obtain a predator/prey balance that allows long-term protection in a small collection.

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Root mealy bugs
These are also very common pests of cacti and succulents, but are found only on the roots of infested plants where they do considerable damage. This may lead to the plant rotting where the damage allows fungal or bacterial infections to enter the plant tissues. They produce powdery white or white fluffy deposits in the soil which may sometimes also be seen underneath the pot. Their general appearance is reminiscent of tiny pinkish-brown woodlice (2-3 mm long) in the soil and roots.

Control of root mealy bugs: Use regular applications (weekly for several weeks) of insecticide (read the label to find pests controlled, use and precautions) watered into the soil, or immerse the plant pot up to the top of the soil in a bucket of insecticide with a couple of drops of washing-up liquid to help wetting of the soil. The plant will need to be carefully dried out after a soaking, especially if treatment must be carried out in cold weather.
As a preventative measure, ground up moth balls added to the potting mix seem to discourage infestation by root mealy bug, and probably discourages other insects. However, the chemicals in the moth balls can cause damage to plastic plant pots and are best used with clay pots. ( NB. In the UK, chemicals must be used only as directed on the label: other use could be considered an offence.) Root mealy bugs also seem to prefer peat-based mixtures to soil-based composts, although not exclusively.

Mice
Field mice may enter glasshouses in the autumn looking for somewhere warm to spend the winter, or at other times in the course of foraging. Mice tend to take a bite out of a lot of potential foodstuffs, rather than eating a lot of one food, and tend to subsequently avoid foods that were unpalatable or harmful to them. Consequently, a mouse may be very destructive to many plants in a short time, especially choice or show specimens which they seem to target carefully.

Control of Mice: Another huge topic. Briefly, mice can be trapped live using special live-traps placed near walls, and the mouse released at a great distance from the house. If you do this, inspect the traps often and put a piece of carrot in the trap to provide moisture, or the mouse may die of dehydration before you find it.

Alternatively, there are conventional traps which kill the mouse and a range of poisonous baits on sale in most good hardware shops. A cat is also said to be an effective biological control for mice.
Rats are really a matter for professional exterminators, but a range of poisonous baits are available to control them.

Red spider mite
The mites are exceedingly small and a strong magnifying glass is needed to see them clearly. An early sign of their presence is the appearance of brown dots where the plant epidermis has been damaged, merging into confluent scarring and sometimes webbing on the plants. The harmful microscopic red spider mites, which damage plants, should not be confused with a commonly seen, much larger red mite 2-3 mm across which is a harmless predator.

Control of red spider mite: The reddish-brown mites thrive in hot dry conditions and dislike humid conditions, so overhead watering and spraying plants may discourage mite attack. They are affected to some extent by insecticides (check labels), but a miticide is really needed to control them properly.

Biological control of red spider mite: A predator Phytoseiulus persimilis is available but requires temperatures over at least 70^oF (21^oC). It is difficult to obtain a predator/prey balance that allows long-term protection in a small collection.

Aloe mite
Tiny mites causing abnormal, irregular bumpy growth on all parts of Aloes

Control of Aloe mite: Cut out and burn all diseased parts in the early stages, or the whole plant in the case of a serious infestation.

Scale insects
These insects have the appearance of flat or slightly mounded waxy, brown scales on leaves and stems. The insect under the protective scale feeds on the plant sap and can transmit virus diseases between plants. A sugary honeydew may be produced and encourage black mould. Scale insects do not seem to be common in the UK, but appear from time to time, particularly on plants put outside for the summer.

Control of Scale Insects: Use regular applications (weekly for several weeks) of systemic insecticidal sprays (read the label to find pests controlled, use and precautions).

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Snails
While these are less traditional pests of succulent plants, they can be extremely destructive if they get into a collection. although unlikely to invade the house, beware of carrying them indoors on the sides of a pot or hidden under a plant. Snails find easy access to greenhouses and cold frames via vents, cracks in the structure and doors left open.
The fleshy succulents are an obvious target for snails, but they even seem to be able to cope with spiny cacti. Having dealt with the spines, they relish scooping large chunks of tissue out of the plant body.

Control of Snails: Generally, careful inspection will allow the culprits to be picked off plants and pots by hand. If you dislike killing these handsome creatures, they must be removed to a distance of at least 200 yards or, being territorial animals, they may return.
If hand picking fails, a range of pelleted molluscicides are available which can be sprinkled between the pots and are very effective.

Sciarid fly
These tiny black flies are also known as mushroom flies or soil midges and lay their eggs in moist soil. The flies are particularly encouraged by peat-based potting mixtures and most bags of peat-based compost seem to include a starter culture, even when sold as sterilised. The flies probably find their way in through small holes in the bags. The flies are weak fliers and generally cluster around infested plant pots and may rise up if disturbed. The translucent white larvae, up to 1 cm long generally eat dead and decaying vegetable material, but may also continue into living roots and upwards into the stem of succulent plants. The conditions used for seed raising also suit the flies and their larvae which will then destroy the developing seedlings.

Control of sciarid fly: The most effective remedy is to use soil-based mixtures and avoid peat. This also reduces the incidence of root mealy bug. Contact insecticides containing Pyrethrum or its derivatives are effective against the adults but eliminating the larvae is difficult. Mixing insecticides such as permethrin with the compost may be helpful.

Vine Weevil
Large gray beetle-like insects seen in the late summer lay eggs in the soil which hatch into fat white larvae with brown heads. These eat the roots and up into the base of stems of plants which then collapse suddenly. The adults nibble leaves and the notches left in the leaves are a warning sign of their presence.

Control of Vine Weevil: When repotting, look out for larvae in the potting mix, and replace all the soil if any are seen. Adding gamma benzene hexachloride (avoid inhaling dust) to the potting mix will discourage the larvae. A new insecticide has recently become available for controlling vine weevil for a whole season by mixing with the potting compost.

Biological control of Vine Weevil: Preparations of nematodes are available which should be watered into the soil and will attack and kill the larvae.

Whitefly
A common pest of leafy succulents, including some Asclepiadaceae. I seem to get whitefly on my Fockea edulis every year and the leafy Euphorbias are also at risk. People growing fuchsias and cabbages will be familiar with these pests, and it seems likely that greenhouse plants are infected from susceptible species growing in gardens or allotments nearby.

Small (2 mm) white flying insects, a little like tiny moths can be seen flying around infested plants and a cloud of these insects rises if the foliage is disturbed. If the under-side of foliage is examined, the immature non-flying nymph stage will be seen, and these must be eliminated to control whitefly, in addition to the adults. The nymphs secrete a sugary honeydew substance that encourages black mould on plants.

Control of whitefly: Use regular applications (weekly for 4 weeks) of insecticidal sprays (read the label to find pests controlled, use and precautions). A single application will not be sufficient to eliminate all the development stages of these insects. Some smoke cones are also effective against whitefly, but again require repeated use.

Biological control of whitefly: The parasitic wasp Encarsia formosa can be used to control whitefly in a glasshouse. The wasps lay their eggs in the immature whitefly, which blacken and die, so a supply of whitefly is required to maintain the predator population. It is difficult to obtain a predator/prey balance that allows long-term protection in a small collection.

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Aphids
The common greenfly and blackfly seen on garden plants may occasionally invade the greenhouse and start a colony on a leafy succulent. The majority of aphids are female and produce a rapid sucession of live young. In the autumn, males appear and fertilise the females so that eggs can be produced to survive the winter. As with other sap feeders, aphids produce honeydew which in turn encourages black mould.

Control of Aphids: Spraying with most insecticides is usually effective. A repeat treatment may be applied after a few days to eliminate any survivors.

Diseases of succulent plants

A range of fungal and bacterial diseases affect succulent plants, some of which can collapse and die very rapidly, once the disease has taken a hold. The world abounds with fungal spores, which are opportunists, waiting for the correct conditions for germination. Generally, fungi do not affect cactus and succulent plant collections because of the relatively dry conditions used by most growers. Damp conditions are a universal requirement for activation of fungal spores, and many of the problems with fungal infection of succulent plants arise from failure of excessive watering or condensation to evaporate, because of unexpected or seasonal cold weather. Damage from insect pests, which penetrate the plant's epidermis to feed on sap, may provide a route for entry of fungi into the nutrient-rich inner tissues. Hence, unexpected collapse of a plant is often the final symptom of a mealy bug infestation which has gone unnoticed. On the other hand, some fungi provide their own mechanisms for penetrating the epidermis.

Seedlings are especially susceptible to fungal attack of the lower stem which causes damping off. Once the seedling has wilted, it is usually too late to save it and preventative measure are a better option.

Some Fungal Diseases

Black or Sooty Mold: A ubiquitous fungus which is often seen on plants covered with honeydew from whitefly, mealy bugs etc or on plants with nectar-producing glands such as certain Ferocacti. Generally, sooty mould is more unsightly than harmful on otherwise healthy plants. However, it will attack seedlings following mechanical damage or excessively wet conditions and other weak or damaged plants.

Basal Stem Rot: Cold or damp conditions may lead to rotting of stems, often just around the soil level where damp soil may be in prolonged contact with the plants stem. The rotten tissues may go black or reddish brown depending on the plant and organism attacking it. If the stem is cut well above the rotten part, it may be possible to re-root or graft the healthy tissues and save the plant. Many people support the basal stems of difficult plants with a layer of grit above the potting medium, so that there will be little water retention against the stem in this critical region.

A range of brown or gray spots spots on leaves and corky brown marks on stems of are undoubtably due to fungal attack following damage or prolonged contact with drops of water. Others may reflect poor cultural conditions or the natural development of corky or woody stems as the plant matures. In many cases, fungal attack and poor culture are linked. Improving ventilation, temperature control, watering and application of fertiliser may help to prevent all sorts of problems.

Growers of Asclepiads will be familiar with black spots developing on the stem which spread and develop into sunken patches of dead tissues. This fungal infection can spread to the whole plant unless the affected part is removed promptly or treated with fungicide. Usually this happens after overal-liberal water, perhaps where water droplets fail to evaporate because of unexpectedly cold conditions.

Control of Fungal Diseases:
Once a plant has collapsed or the stems have started to become soft and rotten it is often too late to save it. However, an attempt may be made to save part of a valuable plant by cutting away the infected tissues with a clean knife, sterilised with methylated spirits. A wide margin of apparently sound tissue should be removed as the infection will almost certainly have spread further than is apparent. The remainder can be painted or dipped in a systemic fungicide such as Nimrod T or dusted with sulphur and rooted as a cutting or grafted onto a compatible stock.

Botrytis or damping off in seedlings can be avoided by lightly spraying the potting mix with a systemic fungicide such as Benlate or Nimrod T. Spraying with a copper sulfate solution is a traditional remedy, but copper fungicides may accumulate in the soil with potential copper toxicity to plants. Any seedlings that become infected should be removed promptly before more spores are produced, the remaining seedlings sprayed with fungicide and surface moisture alllowed to evaporate.

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While these notes focus on pests and diseases of cacti and succulents, incorrect cultural conditions are a major cause of poor growth or loss of house plants in general. The single commonest cultural problem is over-watering, with the roots left wet for excessively long periods resulting in rotting. Other growth problems are related to insufficient light and too low or high a temperature. Most cacti and succulents are expected to flower when they reach the mature size, or even before, and failure to flower may indicate unsatisfactory growing conditions.

Over-watering: is probably the single most common cause of failure of succulent plants to thrive. The plant may appear to do well at first, its leaves plump up and new growth produced. However, the roots may be suffering in wet soil and begin to rot unseen. The plant still looks well as the few remaining roots are able to take up sufficient of the plentiful water. As the roots continue to die in the stagnant soil, a point is reached at which they are unable to supply sufficient water and the plant appears to be suffering from lack of water. If more water is supplied, the situation gets worse and the rot may spread upwards into the basal stems or plant body. Eventually the plant body is observed to be soft and discoloured, perhaps yellow or grayish, by which time it is usually too late to save it. The moral is, that if a plant appears to be failing to take up water, knock it out of its pot and examine the condition of the roots before supplying more water.

Other reasons for loss of roots include pest damage and dormancy. Watering a plant at the wrong time of year when it is dormant can cause rotting as effectively as can also happen if the roots have been eaten by insect pests.

Under-watering: If unsufficient water is provided for the prevailing temperature and stage in the growth cycle, leafy succulents stop growing and may shed their leaves and the apical tip of stems may die. This is followed by die-back or self-pruning of stems and branches. Cacti may shrink back into the potting mixture and possibly take on a reddish or purple hue because of production of coloured stress pigments. In some cases, shrinkage of a cactus during drought produces irreversible folds in the plant body which never fill out again. However, careful watering usually reverses the effects of drought on succulent plants. Small amounts of water should be given to water-starved plants at first, in case some of the roots have been lost.

Poor light: Plants kept with insufficient light grow with pale or yellow sometimes stunted leaves and elongated relatively thin stems with long spaces between the leaf joints. This is known as etiolation. Cacti become soft and elongated with weak spination. The condition can generally be reversed by providing stronger light, although elongated growth in cacti will always remain as a record of the change in growing conditions. Succulent plants can often be pruned to restore their shape.

Cacti and some succulents will not usually become etiolated in dark conditions if kept cool and absolutely dry, and some growers allow their plants to become dormant for winter storage.

Scorch and heat damage: Scorch can affect plants if there is a sudden period of sunshine after the dark winter days, or even after a prolonged cloudy period during the summer. Sunken brown or white patches develop down one side of a plant where the tissues have effectively been "cooked" and the green chlorophyll destroyed. Sometimes a plant loses all its green pigment through excessive heat alone, even though it may not have been in the direct sunlight.

Scorching can be avoided by the timely application of shading to the greenhouse, improved ventilation and air circulation within the growing area to even out air temperatures. When moving plants into direct sunlight, or putting them outside for the summer, harden them off gradually in diffuse sunlight or put them under mesh shading for a few days to acclimatise.

Cold damage: although many cacti and succulents are surprisingly cold-hardy if kept absolutely dry during the winter, some species from perpetually tropical climates (e.g. Madagascar) can suffer damage to the soft tissues at their growing points, and scarring and collapse of their stems leading to fungal attack and death of the tissues. The only solution is to maintain higher temperatures for susceptible plants.

Some species such as Echincactus grusonii which are otherwise easy to grow, can develop unsightly brown marks which spoil a specimen plant, if temperatures are too low

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Plants need at least thirteen elements obtained from the soil, for proper growth, in addition to carbon, hydrogen and oxygen which are obtained from air and water. Plants generally grow normally until they run out of one nutrient, which then limits growth. Deficiency or excess of nutrients often causes discoloured or deformed growth, which may be characteristic of that particular element, although there is a considerable overlap of symptoms.

Most plants will grow better in the long term if additional nutrients are provided by application of fertilisers. Gross excess of some nutrients can induce deficiency of others. The moral is therefore to use balanced mixtures of nutrients in fertilisers, rather than applying a large amount of one element. Many fertiliser mixtures only specify their Nitrogen (N), Phosphorous (P) and Potassium (K) content on the label of the package, but unless especially pure ingredients were used in their manufacture, it is likely that some trace elements will be present fortuitously. Other fertilisers explicitly list their trace element content. The elements are identical whether inorganic or organic ingredients are used, but the source will affect the speed of their release and their availability.

Boron is the only element required by plants but with no function in animals, except that it may be toxic in excess. Borax is the active ingredient in some products designed to kill ants. In most cases extreme measures have to be taken to induce boron deficiency in plants as such low levels are required. However, it has been suggested that cacti may benefit from higher levels of boron and some people add small amounts of borax when watering.

Silicon is also usually ignored as a micronutrient, and will be generally available in any gritty potting mixture suitable for cacti and succulent plants. However, significant amounts of silicon (as silica) may be present in plant tissues (especially in diatoms, grasses, sedges and horsetails) as a structural element. It must be translocated through the vascular system in solution and precipitated, often in crystalline form, under biochemical control to form precisely defined structures.

The N:K balance of some typical formulations are shown below, as quoted by the manufacturers, mainly using examples from the Chempack range which were readily available. This should not be taken as any special endorsement, as other brands will be equally suitable. I like to rotate between several brands to ensure a mix of micronutrients.
For succulent plants, a balanced NPK fertiliser such as Chempack No. 3 is suitable, but cactus growers may prefer a lower nitrogen content such as Chempack No. 8 to ensure that their plants remain compact. Chempak produce a specific cactus and succulent fertiliser with an even lower nitrogen content, in rather small packages. Leafy succulent such as Euphorbias may appreciate a high nitrogen boost (e.g. Chempack No. 2) in the Spring when they start growing, followed by the balanced mixture for the rest of the growing season. For comparison, a typical formulation to encourage tomatoes and other fruit has a very high Potash content as does Cactigrow.

Organic fertilisers may be mixed into the potting mixture when it is being mixed and provide sustained release of nutrients over a long time. The bulky constituents of organic fertilisers help to improve the soil structure. Many organic fertilisers contain essential trace elements and may also encourage beneficial soil micro-organisms. The role, if any, of beneficial mycorrhiza in the growth of succulent plants seems to be largely unknown, despite their demonstrated importance in culture of orchids and many woody plants. However, organic fertilisers will tend to encourage mycorrhyza in contrast to inorganic fertilisers which inhibit them.

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The Elements Important to Plants Macronutrients

Calcium (Ca) Major component of cell walls, important for root tips and growth.
Deficiency: Poor root development with weak tips, distorted curled leaves with hooked tips.
Excess: causes iron deficiency in sensitive plants.

Magnesium (Mg) Essential for chlorophyll formation and a cofactor for many enzyme reactions.
Deficiency: Leaf yellowing with brilliant colours.
Excess: causes calcium deficiency.

Nitrogen (N) Essential for proper leaf and stem growth, protein synthesis.
Deficiency: Reduced growth, pale yellow-green leaves starting with oldest.
Excess: causes potassium deficiency.

Phosphorous (P) Important for germination and growth of seeds, growth of roots, flower and fruit production.
Deficiency: Reduced growth, small bluish-green leaves becoming bronzy-purple or with scorched brown edges and falling off early, starting with the oldest.
Excess: causes potassium deficiency.

Potassium (K) Promotes vigourous growth, disease resistance.
Deficiency: Stunted growth with closely spaced leaves. Scorched brown leaf tips and edges, rolled edges starting with oldest.
Excess: causes calcium and magnesium deficiency.

Sulphur (S ) Essential for protein synthesis and chlorophyll formation.
Deficiency: Slow growth with small, rounded brittle leaves.

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