The Cultivation Page
My own mixture:
As an example, my own potting mixture is based on sieved compost made from vegetable kitchen waste and leaves, weeds and other waste from the garden. This material accumulates and decomposes in a large green 4 ft tall plastic composter, obtained from the local council for a small fee.
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.
Many plant nurseries grow and sell succulent plants in peat based compost. The first thing I generally do with my new plants is to repot them into my own loamy mixture. Repotting provides an opportunity to examine the condition of the roots.
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) except for plants that clearly need to grow in peat e.g. carnivorous plants. Coir fibre is becoming a fashionable alternative to peat, but is said to break down too quickly for use with slow-growing succulent plants like cacti.
Most cacti and succulent plants prefer a slightly acidic compost (pH6). If in doubt, this is the best choice for most species, but also avoid watering with strongly alkaline tap water. Simple, affordable pH meters are sold in many garden centres.
Some species e.g. Echevierias really 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. Geohintonia 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 reaction for use in potting mixtures.
Ideally, succulent 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 or spiny euphorbias 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. I used to use a formulation containing dimethoate biut this is now unobtainable so I use one based on imidacloprid which is less toxic to plants and people.
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.
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.
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Some of these, usually succulent plants from winter rainfall areas (e.g. Lithops, Conophytums and some other Mesembs, Testudinaria elephantipes, Tylocodons, a few Aloes) grow during the autumn and winter months. Their watering should reflect this.
Lithops (left) should be watered from the early Summer to the early autumn (May / June to the end of September in the Northern hemisphere). Flowers usually appear from late August into the Autumn, depending on the species. Water is then withdrawn as the weather becomes colder, and the outer skin allowed to shrivel to a papery epidermis, before watering commences again in the Summer.
Conophytums (left) tend to have an even later autumn / winter growing period, and generally flower at the beginning of their growing season. Watering should be during the late summer - early autumn and spring, with a break during the coldest winter months.
However, keep an eye on the condition of your plants and start watering before they dry out too much, or they may not recover from their resting period.
Most garden lovers and those with specialist collections of plants would agree that a greenhouse is an asset to any garden. Ideally, a free-standing greenhouse for cacti and succulents should be positioned with the ridge running north-south to maximise the light received all year round. A greenhouse positioned so that the ridge runs in an east-west direction will receive more winter light, which could be useful if it is to house mainly succulent plants that grow during the winter. In either case, it is best to avoid locating a greenhouse where it will be in shadow for a substantial part of the day, to near to trees or in areas subject to strong winds. Positioning the door away from the prevailing wind will help to reduce drafts. Areas of land subject to local flooding should also be avoided. If the greenhouse is sited too far away from the house it may be difficult or expensive to provide supplies of electricity or gas.
Greenhouses either have an integral base, or need to be erected on a purpose-built base. A solid floor provides a clean surface under foot and helps to keep out pests. It is an advantage if a solid base slopes slightly to encourage water to drain away. Drainage channels may be moulded in to the concrete to direct water out of the building. However, if you want to plant larger columnar cacti into the ground, then foundations should be constructed around the planting area.
As with the greenhouse frame, staging can be made of wood or metal, with similar advantages and disadvantages of the materials. After watering, plants become very heavy in their pots. Clay pots are heavier than plastic ones and a peat-based compost is usually lighter than one based on loam (e.g. John Innes). Solid staging, while sturdier makes it easier for mealy bugs and other pests to gain access to plants. Slatted staging lets the air circulate, but pests can still move over it fairly easily. Slatted staging is unsuitable for use with capilliary matting or gravel.
There are several methods for heating greenhouses and cold frames during the winter. Electric fan heaters work well, but are expensive. They produce dry heat, so plants require spraying during the winter on sunny days. Tubular electric heaters are available but the plants need air circulation to keep them at their best. If electrical heating is to be used it is worth investigating Economy 7 or similar tariffs. Gas heaters are very successful, but need pipes laid from the house (or heavy cylinders) and installation can be costly. Paraffin heaters work well and are cheap to run, but can produce a paraffin smell, and need to be used carefully to avoid a fire hazard or sooty plants.