Planting next year's flowers in May or June is a very cost-effective way to increase the number of flowers you will have and reduce the cost of buying plants next year. They will grow through most of the summer, producing hardy plants with vigorous root systems that can be planted in the fall to bloom the following spring and early summer. Some biennials can be purchased as seedlings in late summer, saving you time and space.
The plants to plant now are true biennials that grow one year and flower the next, and are usually discarded after flowering. Some are actually short-lived perennials; foxgloves and hollyhocks are classic examples. Other very attractive plants include Campanula pyramidalis, Canterbury bells, Eryngium giganteum, Iceland poppy, Siberian wallflower (Cherianthus allionii), stock (Mathiola incana), and sweet williams. Highly ornamental wildflowers are also worth considering; for example, Scotch cotton thistle (Onopodium acanthium) and weld (Rededa luteola).
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Wallflowers are technically biennials too, but unlike pansies and violas, they don't flower until spring and are therefore often considered bedding plants. The same goes for bedding daisies (bellis), Rudbeckia hirta and forget-me-nots, although the latter will get tangled and mouldy if sown before July.
If you want to grow pansies, polyanthus, primulas, or violas, sow the seeds in a slightly shady spot.
Other plants are true perennials such as delphiniums and lupines. Both of these plants are susceptible to an unruly powdery mildew and, in the case of lupines, aphids, so in many gardens it makes sense to discard them after the first flowering. Seeds are not expensive, but in other cases, if you get a good plant, you can take softwood cuttings from the best specimens and get years of plants for the cost of one packet of seeds.
Popular plants include Archangelica, Columbine, and Oriental Poppy. You can also grow alpine and rock garden plants such as Aubretia, Alyssum, and spreading dwarf campanula as biennials. In fact, it's worth trying any perennial seeds you have now, as most will likely be successful even if you don't sow them in the typical midsummer time.
Many perennials can be sown in early spring to flower the same summer, but this requires greenhouse space and is less reliable than overwintering. Annuals sown now will likely flower poorly and prematurely, so wait to sow seeds until September for spring flowering.
Ideally, sow seeds in a seedbed in bare but moderately sunny ground, such as a corner of your garden, although there may be space on the border to sow seeds where you will grow next year. Rich soils can easily damage the plants, so moderate fertility is sufficient – for example, where compost has been added to the previous crop. These plants generally do not like cold, wet soils, so raised beds are useful in clay soils. Sow seeds in rows to make hoeing easier. Sow 10-20mm deep as shallowly as possible in moist ground, watering the night before if necessary, spacing rows 15-20cm apart.
Plant your perennials now (Photo: Westend61/Getty)
Alternatively, biennials can be planted in pots over the winter or potted up in summer. This is easier to prevent slugs from infesting than in the open, but you should be careful not to overwater, especially in winter.
You want sturdy, stocky plants. Sow sparsely to avoid long-stemmed, weak plants, and in July, replant the seedlings further apart or into smaller pots, as suits you. Plant young plants 25cm apart, with 15cm spacing in each row, and water before planting and after planting if the weather is dry.
Pot your container or cell tray plants into pots. Use 7cm pots for small plants, or 9cm pots for lupines and other larger plants. Fertilize every 2 weeks until late August, and water carefully to ensure the plants are strong enough to plant out in the autumn.
