Recognize the types of plants
The largest group of plants widely grown from seed are annuals that complete their entire life cycle in a single season. These may be hardy, half-hardy or tender, meaning no more than able to withstand life out of doors without protection in the case of hardy, needing some protection from frost in the case of half-hardy, and not safe out of doors until the frosts have finished in the case of the latter. This group of plants provides many of the “bedding” and “pot” plants that are bought each year to fill borders, baskets, and containers. In reality, some of them are actually tender perennials (about which more in a moment) that are grown in our northern European climate as annuals because they keel over with the colder weather. Increasingly with recent winters some of these plants are surviving winter but since they are so easily grown from seed it is best to treat them as annuals.
Popular annuals to sow include snapdragon (Antirrhinum), pot marigold (Calendula), Convolvulus, Cosmos, Dahlia, sunflower (Helianthus), flax (Linum), Lobelia, morning glory (Ipomoea), nasturtium (Tropaeolum majus), Nemesia, tobacco plant (Nicotiana), love-in-the-mist (Nigella), poppy (Papaver), Petunia, Rudbeckia, scabious (Scabiosa), African and French marigolds (Tagetes), Verbena, and Zinnia.
The truly perplexing group of plants for some people are the biennials that are sown one year and complete their life cycle the following year. Perhaps the best known of these is wallflowers and foxgloves. Many of this type of plant can be sown out of doors because they are seeded during summer but there are biennials that are not really biennials but treated as such like polyanthus, pansies, and other types of viola that can be sown as early as March/April. Popular biennials include: Canterbury bell (Campanula medium), wallflower (Cheiranthus allionii and C. cheiri), foxglove (Digitalis), honesty (Lunaria annua (syn. Biennis), stock (Matthiola), forget-me-not (Myosotis alpestris), Iceland poppy (Papaver nudicaule), polyanthus (Primula veris), viola (Viola cornuta), and pansy (Viola tricolour), (click the next button to preview the next page)