If you have a propagator or somewhere warm and light, February or March are good times to start sowing seed, otherwise wait until April. Use a fine well-draining seed compost, or sieve a coarser compost. Soil-based composts (such as John Innes) are good for seed sowing, but mix in about a third of coarse sand, fine grit or Perlite to improve the drainage. Cautious growers may sterilise their compost in the oven for an hour or microwave for three or four minutes.
Use small plastic pots or divide seed trays into sections using plastic strips or labels. Tamp down the compost gently with a jar-lid or similar object to obtain a smooth level surface, then sow the seeds thinly. Large and medium-sized seeds can be spaced out individually, but try to avoid clumping even with small seeds. Push large flat seeds on edge into the compost. To hold the seeds in place and discourage the growth of moss and green slimy algae, sprinkle some of the coarse sand or fine grit on top to bury the seeds to a depth no more than equal to the size of the seeds. Alternatively, put the grit layer on the top of the compost first, scatter the seeds, and wash them down between the tiny stones with a very fine spray.
After sowing, moisten the compost thoroughly by standing the pots in a tray of water to about half the depth of the pot until the surface is damp all over, then allow to drain thoroughly. To reduce the danger of tiny seedlings being attacked by mould or rot, it is a good idea to use a fungicide at this stage, such as Cheshunt compound or a copper-based fungicide.
During the few weeks that may be required for the often sporadic germination and while the seedlings are tiny, the pots should not be allowed to dry out, nor must they be left waterlogged. If you aren't using a propagator, one way to ensure constant moist conditions is to place the pots in polythene bags.
Place the pots in a bright position, not in the dark, but shade from direct sunlight which may scorch delicate seedlings. Normal room temperatures are suitable, but a temperature of 20 to 30°C during the day, dropping to about 15°C at night provides ideal conditions for the germination of many species.
Some species will germinate in one to two weeks, but others will take longer. Expect some failures, but do not be discouraged! Many kinds of cacti and succulent plants will take six to twelve months to reach the size of a pea but will speed up after the first year. Remove the polythene bags or admit some air when the seedlings are growing well.
When the seedlings start to jostle each other, which may be in the same year as sowing for quick-growing kinds or the following year for the slow ones, they will need potting on. Remove the compost in one piece from the pot, separate their roots as carefully as possible, and pot them up individually or space them further apart in fresh compost in another tray. During their first winter, do not allow the young plants to get quite as dry or as cold as their older brethren can tolerate. Watch carefully for any sign of the grubs of mushroom flies (Sciara), which can demolish a pot of seedlings in one night. Modern insecticides, either systemic or contact, will usually help to control them.
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