How to Raise Hardy Biennials
Most of our spring flowering bedding subjects are hardy biennials, or else plants treated as such. There are two ways of raising these plants depending upon their mode of growth. Wallflowers and sweet williams are easiest raised in drills in the open ground, while forget-me-nots, pansies and polyanthus are best grown in trays or pots. All are sown during mid-summer in order to produce plants that are strong enough to be able to withstand the winter.
Plants that are best raised in the open garden are sown in shallow drills made with the edge of a swan-neck hoe in a nursery bed. This need not be a special part of the garden separated for the production of young plants, but can equally well be, and often is, a corner of the vegetable plot. If this is what you intend to do with wallflowers, be careful to include them in the section reserved for cabbages, cauliflowers and sprouts, for like brassicas, wallflower are subject to devastating attacks from club root disease and therefore could upset the rotation of your vegetable plot.
Before sowing, water the open drills and ensure that the soil is thoroughly moistened. The seed can then be distributed thinly along the bottom of the drill and back filled; if the weather is dry, water the drill again. Seedlings of wallflowers appear within a few days and so it is as well to be ready to dust them with derris dust as a precaution against flea beetle.
Once the first few adult leaves have appeared the vigorous young seedlings should be transplanted into nursery rows about 10 cm (4 in) apart with 25 cm (10 in) between the rows. As soon as these transplants have become established, the growing points should be pinched out so that they bush out and become more substantial plants. Within reason, the larger the plants, the fewer that will be required.
Open-ground plants can be moved to their final positions any time after the summer bedding has been cleared away. It is difficult to establish spring flowering bedding subjects after mid-autumn, so if the season lingers, the summer bedding must be removed and the soil prepared before then. Adequate soil preparation is vital for the success of these subjects, although fresh manure is not desirable. A slow release fertilizer (e.g. bonemeal) applied before planting, together with very firm planting will ensure the success of most spring flower subjects.
