Introduce a few self-seeders

These happy-go-lucky plants allow a colour scheme to relax

Self-seeders are an essential element in a cottage garden. They add a random note to a border, popping up where they please. Many are too generous and it’s a good policy to leave one in 10 heads to self-seed and cut the others away. Candidates for this treatment include aquilegias, sweet rocket (Hesperis matronalis), opium poppies and love-in-a-mist (Nigella damascena). Aquilegias need moist soil and part shade. Some seed strains come true to type and A. vulgaris ‘Ruby Port’ and ‘Nivea’ are both excellent. Fragrant sweet rocket is another excellent choice, with May flowers in soft-purple, silver-mauve or white. The long seedpods can be left, but plants live far longer if cut back after flowering. A favourite of the day-flying hummingbird hawkmoth, Centranthus ruber starts to flower in early May and, if deadheaded, will continue until November. Cutting back the entire plant in mid-July lengthens its lifespan; it soon recovers. The Moroccan form, Centranthus lecoqii, is a soft mauve alternative. Opium poppies (Papaver somniferum) provide strong structure and silvery foliage topped by single or double flowers. Poppy seeds only germinate in light, so it’s a good idea to fork over the soil where they’ve been. Nigella, meanwhile, has feathery foliage and wispy blue flowers that curl through a border like smoke. Although the seedheads are attractive, only leave a few. Annuals and biennials are excellent bee plants and one of the best is the cornflower, Centaurea cyanus. These are a perfect partner for orange pot marigolds or calendula. Add in some blue larkspur and frothy, lime-green Bupleurum rotundifolium ‘Griffithii’, and leave them to get on with it.