Sowing wildflowers

General information

Obtaining seed

Wildflower seeds are now available in huge variety from specialist suppliers, with John Chambers for example, listing over 300 species. Most seeds suppliers supply seed from stock of British provenance. This has been obtained by collecting seed from native or naturalised plants in the wild, from which stock plants are grown in the nursery. From these plants the seeds are harvested each year. Avoid buying seeds which are not of British provenance. Seeds should also be native strains, not agricultural cultivars, of species. Agricultural cultivars are named strains of a species which have particular value for agricultural production, but are visually and ecologically unsuitable for wildflower plantings.

Most seeds suppliers sell wildflower seeds as mixes of different species. These mixes are chosen to suit different types of site and for different uses. Favourite mixes include ‘cornfield annuals’, ‘butterfly plants’, ‘chalk downland’ and ‘damp meadow’. Some mixes are wildflowers only, whereas any ‘meadow’ mix will include grass seed, usually in the ratio of 20% wildflower seed to 80% grass seed. The grass provides the year-round matrix amongst which the flowering perennials will grow. Annuals are usually sown as a mix of wildflowers only, as no perennial component is wanted.

Seed mixes are difficult to ‘read’, and results hard to predict without experience. Species comprising a mix may be listed by % weight, or by % number. numbers of seed per unit of weight vary greatly between different species. A seed mix may appear, for example, to have a high proportion by weight of a particular species, but if this species has relatively heavy seed, the actual proportion of seed will be quite low. The clearest way to present a seed mix is by weight and seed number, as in the ‘Cornfield Annual’ mix below, supplied by Landlife.

Some seed mixes are simply a list of species, with no details of proportions, and the customer has to trust the seeds supplier to supply a balanced mix. Species also vary in speed and ease of germination. Some species have almost 100% germination, while others are much more erratic. The seeds supplier should take this into account when selecting the mix.

Catalogues and other literature from suppliers contain helpful information on growing wildflowers from seed. For larger areas, seeds suppliers will supply mixes made up to the customer’s requirements.

Each year there is a limited supply of seed harvested from existing sites, including SSSIs and nature reserves, which is available to purchasers. These will contain a large number of species in unknown proportions.

As an alternative to purchasing seed, do-it-yourself collection is possible. note that collection of seed from some rare species is illegal. For other species, you should only collect seed with the permission of the landowner. Collection of individual species by hand is laborious, and seed needs to be stored carefully after collection. An alternative method is to harvest seed mechanically from an existing meadow. This can be done by cutting the meadow at the time when most of the desired species are setting seed, collecting the cuttings and spreading them to dry on the new site. A forage harvester can be used on a large site, or a mower with grass box on a small site. The harvesting time is critical. Too soon, and the seeds will not have ripened, too late and the seeds will already have dropped. Specialist vacuum seed collectors are also used for collecting seed from existing habitats. For basic information on seed collection and storage see Emery, Malcolm (1986).

Grasses

Annual wildflowers should be sown without any grasses, as no perennial growth is wanted. Biennial or perennial wildflowers on stony banks and mounds or other ‘stressful’ sites can grow in the long term without a significant invasion of grasses. On any cultivated ground, grasses are likely to appear from seed already in the ground, or from seed spread from surrounding areas. The proportion of grass also needs to be related to the use of the site. Grasses are stimulated by cutting and trampling, whereas other flowering plants are not. If the site is trampled, grasses will inevitably be favoured, and indeed will be needed to avoid the site becoming bare ground. Traditional meadows with wildflowers, grazed or cut for hay, are basically grasses with a proportion of other flowering plants.

Most wildflower meadow seed mixes are sold as 80% grasses, and 20% wildflowers. This proportion gives a suitable balance between the matrix of grasses and the more seasonal growth of wildflowers. The grasses should be slow-growing, ‘low-maintenance’ grasses, but may be commercial cultivars. True native grass seed is available in limited quantities from some suppliers.

Sowing rates

The seed supplier will advise on the optimum sowing rate for the particular seed mix. For annual wildflowers only, this is 0.5-2g per sq. m. For wildflower/grass mixes (20%/80%) the rate is 3.75- 5g per sq. m. Seed sowing using an agricultural seed drill is very efficient, encouraging maximum germination, allowing a lower rate of 1g per sq. m for wildflower/grass mixes.

Stratification

Some species require cold treatment, called stratification, before they will germinate. This occurs naturally for seeds sown in autumn. The species listed, if sown in spring as part of a mix, will not germinate until after the following winter. If supplied unmixed, these species can be given an artificial ‘winter ’ to speed germination. Mix the seed with damp sand in a plastic bag, and leave it in a refrigerator for 6-8 weeks.