HINTS ON LOOKING AFTER YOUR CACTI & SUCCULENTS IN THE UK
Light: almost all these plants will benefit from giving them as much light as possible: a greenhouse is fine because it allows light from all sides to benefit the plants, a raised frame with glass top and sides in the garden is a good second best, or the sunniest windowsill in the house should be given if the first two options are not available. Some shading may be necessary in a glasshouse in the hottest weather, particularly for some succulents, like Conophytum (particularly susceptible to scorching in the first sunny days in spring), or for some which grow in the shade of grasses or bushes.
Temperature: provided the plants are kept dry at the root in the coldest of the winter months, most will survive temperatures down to nearly freezing, but 5º C (40º F) is safer. Genera which need higher temperatures (minimum 10ºC/50ºF) are Melocactus, Discocactus, Uebelmannia, some Euphorbia species, and some of the Stapeliads.
Watering: water should be withheld in the coldest months, especially if your plants are likely to have to put up with low temperatures. If in a cold (not heated) or cool glasshouse (minimum 5ºC) watering should not continue after the end of September, and should not commence again until mid-March. In the dwelling house, or if a minimum of 10ºC is maintained in the glasshouse, watering can go on until the end of October, and can recommence at the beginning of March. But in the spring make haste slowly, allowing the plants to dry out almost completely before repeating the watering, and not watering freely until the middle of May - even then and thereafter allow the soil to almost dry out between waterings. When you do water them, in the summer months especially, make it a proper watering, as much as you would give other house plants, and incorporate a high potash feed (as used for tomato) every other watering. But do not leave them standing in a saucer of water for more than half an hour - pour away the water left in the saucer after this period. Slow down the rate of watering in early September, and withhold water as indicated at the start of this paragraph for the autumn and winter. There are some winter growers, especially in the Mesembryanthemaceae family (Lithops, Conophytums etc), seek more particular advice on the watering of these plants.
Repotting: repot every year in the first few years, until plants get into pots about 10cm wide, when they can be left a year or two before repotting. A good soil-based compost is recommended, with one part of coarse grit to two parts of compost, to improve drainage, a vital factor in growing these plants satisfactorily - they do not like water around their roots for too long. Perhaps the best time to repot is in late winter/early spring, before watering starts, allowing at least two weeks after repotting before watering.Use almost dry compost, and avoid breaking the roots as much as possible, although most of the old soil can with benefit be shaken out of the roots before repotting. Check at this time for root mealy-bug - see below.
Pests: the worst pests are mealy bug (white cottonwool-like patches on the plants, or on their roots), and red spider mite, almost invisible to the naked eye, but the mites turn the skin of the plant they are infesting a light brown. Removing with an old paintbrush, and spraying with an insecticide is recommended for the first, and spraying with a pesticide specifying red spider mite is recommended for the second. Seek expert advice on both. A recent introduction, PROVADO, seems to work well on most cactus and succulent pests, as well as its specified Vine Weevil use.
The British Cactus & Succulent Society: this society has branches all over the UK, and you are recommended to seek out your local branch. They usually hold monthly meetings with an invited speaker often showing slides of a trip overseas or about a particular group of plants. Information about the branch is usually to be found in the local library, or ask when you order and I will gladly provide information about your nearest branch. The Society also issues a quarterly, colourful and informative journal. Annual subscription is £15 for UK Membership (UK Junior Membership £6; Over 65 £12); send cheque payable to the B.C.S.S. to Tony Morris, 6 Castlemaine Drive, Hinckley, Leicester, LE10 1RY.