Seeds of non-hardy or half-hardy plants have to be sown indoors with gentle heat in pots, seed trays or cell trays filled with good compost.
This technique is used for tender plants that can take several weeks from sowing seed to flowering, but can’t be planted outside until frosts and cold weather have finished. These half-hardy annuals and half-hardy perennials include aster, begonia, geranium (pelargonium), petunia, busy lizzie, French marigold and dahlia to name but a few.
Some vegetables are best grown in this way and include tomatoes, aubergines, peppers and cucumbers as well as runner beans, sweet corn, courgettes and marrows.
Many other vegetables can also be started into growth in this way if you want to start them earlier in the year and so produce an earlier crop.
Seeds can be sown in this way early in the year (January to February), providing you can give them the right germination temperature and good light to prevent the seedlings becoming drawn and spindly. It is also important to have a good growing on temperature - for most plants this is a constant minimum of 7-10°C (45-50°F). If you can’t provide these conditions, delay sowing until spring.