PROPAGATION FROM SEEDS
Many species of cacti and other succulent plants are relatively easy to raise from seed providing that a few simple rules are followed. Seeds of an unprecedented range of species of cacti and other succulent plants are available from both specialist society seed lists and commercial seed suppliers, so that with a little patience, a large collection of plants can be raised from seed and flowered within a few years.
Seed may also be available from your own plants, and is freely produced by some species e.g. Rebutias. It is well worth attempting to grow seed from your own plants and this fresh seed may germinate more readily than seed from other sources. Seeds from different species survive for different lengths of time before losing viablity. Lithops seed can survive dry for many years while seed from many Asclepiads is best sown fairly fresh.
Seed is best sown in small individual containers, although large quantities can be sown in seed trays. Seed trays can be divided into sections as required, with thin wood or plastic strips such as seed labels. If several species are to be sown in strips in one container, it is best to choose species that can be readily distinguished from each other, as occasional seeds tend to bounce from one area into another during sowing.
Many growers prefer a soil-less compost, with the addition of about one part in three of sharp sand to improve drainage and texture. Partial sterilisation of the soil is useful and may be achieved by either baking in a conventional oven for a few hours, or by treatment for a few minutes in a microwave oven. Following such treatment, the compost will not be clinically sterile but will be free of insect pests and their larvae and will have a reduced burden of fungi and other micro-organisms. Complete sterilisation is undesirable, as the first infecting fungal spore landing on the compost produces a white bloom of fungal hyphae over the surface a few days later, and subsequent damping off of the young seedlings.
Some species from environments with cold winters may require exposure to cold or even freezing conditions to break dormancy (simulating natural passage through a winter).
Several strategies may be tried:
- Sow seeds in January and cover with fine grit or sand. Water so the compost is moist and place outside where a range of natural freeze-thaw temperature cycles will be experienced.
- Sow seeds, cover and place the container in the refrigerator for several weeks.
- Sow seeds, cover and place the container alternately in the refrigerator and ice compartment of the refrigerator over several weeks to simulate freeze-thaw cycles.
- Seeds of other species are activated by chemicals found in the smoke from bush-fires and kits are now available containing synthetic concoctions of these substances.
Prior to sowing, the compost should be moistened by standing the container in water, or by spraying a mist of water onto the surface. Adding a fungicide (e.g. Benlate, Nimrod T) to the water can be helpful in combating 'damping off' of seedlings of some species.
Seeds should be cleaned of unnecessary debris and the silk 'parachutes' of some seeds (e.g. Asclepiads) removed. Unnecessary plant material is always a potential focus of fungal infection and may promote 'damping off'.
Most small seeds can be distributed over the surface of the compost, and may be covered with a very light dusting of sand. Although this is not strictly necessary, it can help to supress growth of algae and moss. The emerging seedling roots will generally anchor themselves into the compost. Any roots that emerge at an awkward angle, pushing the seedling away from the compost can be covered with a sprinkle of sand.
Very large seeds can be sown individually into holes made in the surface of the compost with a small stick or plant label, and it may be helpful to scarify the seeds or pre-soak in water if there is a waxy protective seed-coat.
Following sowing, the seed should be kept in a moist environment in a propagator, or the whole container wrapped in a clean plastic bag. Following germination, alternative strategies used by different growers are to remove the covers after e.g. 1 month to allow the circulation of air or to leave the seeds sealed up in their containers for up to a year. Whichever method is followed, it generally advisable to avoid the compost drying out for about the first year, and watering with fungicide may help survival of delicate species. Seeds may continue to germinate over a long period of time and it should not be assumed that the first seedlings are all that will be obtained.
Minimum temperatures of 60 - 70°F are usually desirable and will allow germination of the majority of succulent plant seeds, but some tropical species may require warmer conditions. Germination does not usually appear to be inhibited by light, and may be essential for some species, but bright sunlight should be avoided as the delicate seedlings may be scorched. As the seedlings grow, the amount of light given can be gradually increased, but beware of direct sunlight.