There is a variety of techniques that can be used to grow plants from seed and gardeners are encouraged to attempt a number of different ones. Much of our early experience in growing from seed involves the purchase of packets of flowers and vegetables from commercial suppliers, planting in punnetts or in open beds often with considerable success. It is when we attempt to grow unfamiliar plants from seeds that we may be less successful and so some general advice is offered here on techniques to try.
1. Pots of seeds/seedlings in pots kept in polythene bags
For many species, growing the seedlings in pots enclosed in a polythene bag is a virtual necessity. Thin film polythene bags are recommended to allow sufficient diffusion of oxygen into the bag; close it at the top with a wire twist but not so tight as to totally seal the bag. Moisture conditions inside the bag are maintained and this avoids the alternate overwatering and drying out that plagues open pots. Before sowing the seeds it is important to sterilise the potting mix by pouring boiling water over the pot three times and allowing it to drain each time. Sow the seeds on the cool surface and enclose the pot in the bag. The sterilisation destroys insects and other life injurious to the seeds and inhibits the growth of moss and algae. Temperature maintenance is also important when growing in bags. Placing pots in bags in the direct sunlight is not recommended since temperature rises could cook the seeds. The use of fluorescent light (or for the home gardener) indirect light in a warm room should be sufficient.
2. What type of pots should be used?
There has been a long-standing argument between those who use old traditional clay pots and those who use plastic pots. The porosity of the clay pots allows you to get away with over watering. However, the bagging technique obviates all of this so there is no question that plastic pots should be used.
3. What medium should be used in pots?
The medium used most frequently is composed of equal parts of peat moss, leaf mould and Perlite. This has a high water holding capacity due to the Perlite which helps prevent drying out. It also has a high free air space. This gives high aeration which is important with seedlings because they have actively growing roots which consume air rapidly. The home gardener can be reasonably confident in using one of the propriety seed-raising mixes with perhaps the addition of some Perlite.