Events

Flowers from The Cape

Terry Smale (author, lecturer and nurseryman)

Geophytes (bulbs, corms and tubers)

The term bulb is often used in a general sense to describe true bulbs, corms and tubers; the more accurate but less familiar collective name for such plants is geophytes (meaning earth plants). These plants have adapted to life in climates with seasonal rainfall by disappearing below ground during the dry season. The subterranean organ is a gene bank and food store that enables flowering and reproduction when conditions are favourable during the wet season. Thus they have developed a different but complementary survival strategy to succulent plants for coping with life in areas that have prolonged dry spells. Geophytes grow wild over much of the winter-rainfall region of South Africa and within this area, they are all winter-growers even if they originate from habitats that also experience some precipitation during summer. Certain genera such as Haemanthus, Ornithogalum, Gladiolus and Moraea also contain summer-growers from outside the region and it is necessary to check growing seasons using books or catalogues or by reference to geographical distribution.

Cultivation of Geophytes

Temperature & situation

In the main, the hardiness of these geophytes in Britain has not been tested, although a few examples such as Amaryllis belladonna have been shown to succeed in sheltered spots in the open garden in the south. There are also reports of Gladiolus, Tritonia and Ixia species surviving in very well-drained situations outside. However it is advisable to grow these bulbs in a frost-free greenhouse or conservatory until one has enough material to experiment with. In the wild, many montane species from areas such as the Cape mountains, Kamiesbergs and Roggeveld plateau experience significant frost while in growth and should be temperature hardy. Therefore try growing spare bulbs in a cold frame or unheated greenhouse with either a free root run or pots buried in a plunge; even Eurasian bulbs such as narcissi and crocuses can sometimes be killed if their roots are frozen. Certainly, various Lachenalia, Massonia, Polyxena, Gladiolus and Tritonia species can be grown in this way. Overhead glass enables control of watering and resting seasons can be respected, but ventilate the greenhouse or frame whenever outside conditions allow.

Potting

In the wild, South African bulbs grow in a range of different soils, but in nearly all cases they are well-drained and relatively low in nutrients; this should be reflected in the potting medium. A suitable mix consists of 2 parts 4mm grit, 1 part John Innes Compost No. 2 and 1 part ericaceous compost, but other free-draining mixes will be suitable. Repotting should be carried out about every two years while the plants are dormant. Old roots and tunics are cleaned away and the bulbs in most cases can be put back in the pots quite close together, for example 25 Lachenalia in a 13cm pot. The only exceptions are bulbs with broad prostrate leaves such as Massonia, which need room for the foliage to develop naturally. Plant bulbs quite shallowly in the first instance: Amaryllids (members of the family Amaryllidaceae such as Haemanthus and Nerine species) with their nose at soil level and others with it about 3cm below the surface. When subsequently repotting certain species, it will be noticed that they have pulled themselves deeper into the soil by means of contractile roots; these bulbs should be put back at the depth that they have indicated they want to grow. The flowering of many amaryllids is inhibited by repotting and therefore when these are getting close to flowering size they should be left well alone. Furthermore, a few amaryllids such as Boophone disticha grow with their bulbs above the soil. Plastic pots are suitable for bulbs in the frost-free greenhouse but clay pots or aquatic-plant baskets are better for material plunged in the cold frame.

Watering & light levels

South African winter-growing geophytes require a warm dry summer rest; if they do not get this they will sometimes fail to produce growth in the autumn, although the underground organ remains sound and might sprout in future seasons. Watering is started at the beginning of September and continued through the winter until foliage starts to die in April/May. Watering in mid-winter should be done with caution and it is advisable to wait until a slight limpness in the leaves indicates that water is required. During the main spring flowering season, watering needs to be copious. Since the bulbs could originate anywhere from the relatively wet Cape Peninsula to the dry Richtersveld, a little research about your bulbs could help in tailoring watering to particular needs. During the winter, the growing bulbs will need all the light that can be provided for them in order to keep their typical characters; artificial lighting could be advantageous. A consequence of poor UK winter light levels is that foliage and flower stems tend to elongate too much. High nutrient levels will also contribute to this, so give very little feed once bulbs reach flowering size. Some shading of the plants from the end of March will help to keep them in growth for as long as possible and therefore produce large flowering bulbs for the next season.

Pests & diseases

Viral diseases are common among commercial bulb stocks and usually manifest themselves as pale streaks on the leaves and perhaps distorted flowers. There is no easy cure and such material is best destroyed. Viruses are carried between plants by aphids, therefore any infestation of these should be immediate eliminated using a suitable insecticide. Mealy bugs sometimes occur among old scales around the tops of bulbs; this is one reason for cleaning away dead scales and tunics when repotting. If mealies are present then treat with a suitable insecticide such as one containing imidacloprid. Finally, flowers that appear during humid weather in autumn and early winter are often infected by botrytis as they die. If the dead flowers are not removed, the fungus can transfer to the leaves and eventually to the bulb, with fatal consequences.

Propagation

Vegetative reproduction

Many geophytes produce underground organs that divide or produce tiny offsets. These can be separated out at repotting time and thus stocks of a single clone built up. Where this does not happen, true bulbs can be forced to produce offsets by twin scaling or removal of the base plate. The grower should refer to a specialist manual if these techniques are to be attempted. An easier technique is leaf cuttings, which have been shown to work for some Lachenalia, and Haemanthus species. Cut off half a leaf as soon as it is well developed, but fairly early in the growing season, and insert the cut end into gritty compost. If all goes well, it will root and produce a number of bulbils by the end of the season. Any virus infection will be transferred during vegetative propagation, that is why seed is to be preferred.

Raising from seed

The best selections of seed of geophytes is available from South African sources. Catalogues are published around Christmas-time, therefore that is when seed tends to be purchased. However, the seeds of many species need a warm period to complete the ripening process and may not germinate well if sown immediately. Seed of winter-growing bulbs will germinate naturally in autumn when temperatures are falling, so store it unrefrigerated until early September. Sow seed, just a few millimetres deep, in the same compost as used for adult plants; a 8cm deep, 7cm square plastic pot is big enough for a packet of 25 seeds. Place the pots in a shady cold frame, keep compost moist and they will usually germinate by the end of October when they are brought into the greenhouse. Occasionally seeds will not germinate during the first year; any empty pots should be dried off and then watered again at the start of the next growing season. Space out bulblets during their first dormancy and many will flower at two or three years old; feeding during the early stages with a tomato-type fertiliser will shorten the time to flowering. Seeds of all South African amaryllids except Cyrtanthus are viable for just a few weeks and must be sown immediately. If the seeds are sourced from South Africa they will usually be available in April - May; the wrong season for us. They must still be sown on arrival and kept in the coolest shadiest spot that can be found. They can often be kept in growth for nine or more months and then brought in phase with our seasons.

Specialist Society

The Indigenous Bulb Association of South Africa (IBSA): produces annual Bulletin, monthly newsletters, annual seed list and organises conferences and field trips. Contact address: PO Box 12265, N1 City 7463, South Africa or mailto:rachel@silverhillseeds.co.za