Propagation
Plants can be increased in a number of ways. For example, they can be reproduced from seeds, from cuttings, by division of the roots, by separation and replanting of bulb and corm offsets, and by layering.
Many of these techniques are quite simple and more often than not successful. The more difficult ones – such as grafting and budding – are more of a technical challenge, and are not dealt with here.

How to sow seeds
Growing plants from seeds is perhaps the most interesting and satisfying way of increasing your stock, but for the best results the conditions must be correct. Moisture, oxygen and a suitable temperature are essentials, and while most seeds germinate in the dark, some prefer the light.
The sowing instructions on the seed packet will usually list the plant’s requirements, but generally speaking it is the fine seeds, such as those of begonias, which need light.

GERMINATION UNDER GLASS.
Before you start, thoroughly clean containers and propagators with a proprietary garden disinfectant. Treat wooden seed boxes with a wood preserve.
The compost must be free of pests, diseases and weed seeds, so use a proprietary brand of a soil-based John Innes seed compost, or a soil-less compost containing peat or pulverised bark with possibly vermiculite, perlite or sand.
Sow the seeds of acid-loving plants, such as heathers, in an ericaceous, or acid, seed compost.
Some seeds need special treatment before they are sown.
Those from trees, shrubs and some alpine plants need stratifying – exposing to low temperatures – before they will germinate.
Whatever the size of the eventual plant, most seeds from these plant groups should be sown in trays in autumn, and the trays overwintered outside or in a mouse-proof cold frame.
Some small alpine seeds can be stratified in a fridge.
Mix the seeds with a little moist peat and sand (50/50 by volume) in a plastic bag and place in a cool drawer of a fridge for 4-8 weeks. This will break the dormancy, so that the seeds will germinate once they are placed in the warmth. Sow the lot – seeds, peat and sand.
Soak hard-coated seeds such as sweet peas, cyclamen and lupins for about 24 hours in water, or between layers of damp tissue, until they swell. Any that don’t can be encouraged by removing a small amount of seed coat on the opposite side to the eye.
Some fine seeds are best sown immediately after harvesting, for example, primulas, gentians and meconopsis, none of which should be covered with soil. Protect all seeds placed outside from vermin and birds with small-mesh wire netting or gauze.

DEALING WITH HALF-HARDIES.
Sow half-hardy annuals and half-hardy perennials between midwinter and early spring, under cover, in temperatures of 13-24°C (55-75°F), preferably in a heated propagator.
Start with those that take a long time to germinate and to develop flowers, like Begonia semperflorens and lobelias, followed by mid-term plants like French marigolds and ageratum, and finishing with later-flowering plants like China asters.
Choose a container of the correct size – you can get 100 or more seeds in a seed tray, and 20-30 in 3 ½ in pots.
Do not sow more than one variety in each container.
If they germinate at different times there will be problems when the time comes to harden off the seedlings – that is, to acclimatise them to lower temperatures.