Xerophytes & Geophytes
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CULTIVATION OF CONOPHYTUMS
Conophytums grow in the western part of South Africa and also in south-west Namibia. This area has a Mediterranean climate with rain falling in the winter and with dry summers. Therefore plants in the wild are winter-growing and conos persist in this behaviour in cultivation. Their treatment is fundamentally different to that of cacti and it is worth separating them in the greenhouse and keeping them alongside other obligate winter-growers such as Cheiridopsis, Tylecodon, Bulbine, etc. Please note that these cultivation notes are based on my experience in northern Europe and that your methods might need to be somehat different in other climates.
Conophytums have a summer resting period, during which time the existing leaves dry up and protect the next-season’s leaves in a papery sheath. Watering is resumed at the end of July and is quite heavy for about two months, perhaps once a week depending on weather. During this period the new leaves develop rapidly, splitting the old sheath, and in most species the flowers are produced. As the weather deteriorates in the autumn, watering is gradually reduced in frequency to a level of about once every three or four weeks through December and January. Frequency will depend on external weather conditions and may be more frequent if particularly sunny, or less frequent if cloud-cover persists for long periods. Certain species, e.g. Conophytum calculus, start to produce obvious wrinkles when they need a drink and I use these as marker plants to determine when the collection needs water. Around about mid February, the conditions start to improve and frequency of watering is increased once more; it is during this period that the new leaves are starting to form inside the existing ones. Watering is stopped in early April and the plants enter their resting phase. I do not water my conos at all during the summer, but some successful growers do continue with very light watering, particularly of the smaller-headed species. Please note that any spraying or overhead watering during this period can result in tannins being leached from the sheath, discolouring the new heads below. I like my mesembs to grow as hard and compact as possible, therefore feeding is much less than for cacti. I use low-nitrogen liquid feeds, e.g. Chempak 8, once during early spring to help the new leaves form and also once in the autumn if plants have not been repotted.
The beauty of many conos is in their coloration and high light levels are needed during the growing season to maintain this. Therefore during the winter, plants should be placed in the brightest possible position in the greenhouse. Even if you do this, the amount and intensity of winter sun in the U.K. is very low and there is a tendency for plant bodies to become very green and soft. About the beginning of May, we often experience our first very hot and sunny days of the summer and there is a big danger of conos scorching at this time. In fact this is probably the biggest problem in growing the genus. The effect of the sun is often not seen until plants start growing in the autumn, when south-facing heads on the clumps are seen to be dead. In an attempt to avoid this problem, I paint white shading on the glass over the conos in April; removing it again in September. Alternatively if you have a small collection, move the plants to a shadier part of the greenhouse for the summer.
In the wild, some of the conos that grow at higher altitudes do experience frost and snow, but of course the climate is not so humid as in the U.K. It should be possible to select some conos to grow under unheated glass (a Kamiesberg form of C. pellucidum is happily growing in the Wisley alpine house) but in general I would recommend frost-free conditions. My greenhouse does not go below 3oC during the winter. Good ventilation is needed in summer and try to avoid temperatures over 40oC.
I always use plastic pots for conophytums; clay pots in small sizes dry out far too quickly. In sizes of 9cm and over, use pans rather than the deeper pots because most conos are shallow-rooting. Very small plants are best grown several to a pot to avoid too much unused compost. My standard mixture is equal parts of John Innes Compost no. 2 (J.I. is a sterilised loam based potting compost) and 4mm quartzite grit, but any free-draining loam-based soil mix is suitable. Ideally plants should be repotted about once every two years, but I have many plants that have been untouched for much longer. The best time to repot is early in the growing season, July-August, but it can be done at almost any time while the plants are in growth. There actually seems to be more new root formation during the winter than in the autumn. Clean as much of the old compost from the roots as possible using a pointed label or stick and a small brush.
The genus is relatively trouble free but root mealy-bug can sometimes occur. Watering with a suitable insecticide (imidacloprid is particularly good as the active ingredient) once during the autumn is suggested as a prophylactic measure. Western flower thrips are often seen on cono flowers, but they do not seem to do any damage. Spraying with a contact insecticide during the growing season will provide some control. Sometimes snails and tortrix moth caterpillars start munching the plants and both are best hunted at night. General hygiene and appearance of conophytums is improved by carefully removing old sheathes after the new leaves have broken through. Removal of dead flowers avoids them becoming a source for botrytis.
Old plants that are fifteen or more years old, tend to loose vigour and are best broken up into cuttings. You can also propagate desirable plants by removing growths from around the edges of a clump, but I often find it easier to knock the plant out of its pot to do this. In both cases, cuttings should be taken after the leaves have developed properly in the autumn, usually September-October, but I have even taken cuttings successfully in February. A cutting should consist of just one or two growths with no more than a couple of millimetres of stem below. No callusing, propagator or bottom heat is required, just plant in suitable compost (I use 2 parts J.I. no.2, 1 part 4mm grit, 1 part Perlite), put in the greenhouse with your other conos and water them. Rooting should take place within one or two months.
Cono seed is now available from several sources; the best of which are Mesa Garden in New Mexico and the Mesemb Study Group. If you want to produce your own seed, it will be necessary in most cases to have two different clones of the species. These should then be isolated in some way to prevent any unwanted pollination. Pollen is transferred between flowers on separate plants using a suitable tool. I use the follicle end of a human hair, but a cat’s whisker, cactus spine or a fibre from shade netting are used by various other people. Once flowers have faded, the plants can rejoin the collection. Seed capsules take a long time to develop and I usually harvest seed in the following August. In the wild, seed would germinate in the autumn with falling temperatures and the advent of rains. Autumn is therefore the natural time to sow and is indeed the best time in sunny places such as California, Greece and Spain. However in my experience, seedlings that have germinated in the autumn in England are very prone to fungal attack and subsequent loss. Therefore I compromise by sowing in January. My compost is 2 parts John Innes Seed Compost, 1 part 1mm grit, 1 part Perlite. Seed is sown on the surface of the compost at a rate of 20 - 40 to a 5cm pot, 100 to a 7cm pot. I do not carry out any additional sterilisation of the compost, nor do I use any fungicides. Temperature for germination should not be too high, 15 - 20oC during the day falling to 5 - 10oC at night. This can be achieved using a windowsill in the dwelling house or a low wattage heating pad in the greenhouse. The pots should be kept moist and can be kept in a closed atmosphere until germination starts in one to two weeks, then allow free air circulation. The seedlings are watered and kept growing for the first 15 months and to achieve this, they must be heavily shaded and kept as cool as possible from March onwards through the summer. The cotyledons will usually dry up at some point during the summer, but the first true leaves will break through shortly after. I line the seedlings out in quarter trays in November and many will flower in the following autumn when about 21 months old. I feed seedlings quite frequently to help them develop as rapidly as possible.
Many species of Conophytum are very variable and the gardener needs to be able to identify particularly interesting forms. In some cases there are old Latin names, which are not used these days by more conservative botanists, that come to the rescue. You will often find these names used on lists and labels in inverted commas. Thus Conophytum ectypum ”tischleri” defines a yellow-flowered form of a particular species that is usually pink-flowered. The original locality written on the label is also important in identifying attractive variants, so if “tishleri” came from Aribies it would have a plain green body, whereas the form from Eselsfontein is covered with a network of dark lines.
Originally published in the "Bulletin of the Mesemb Study Group".
© Terry Smale