Annual wildflowers can give a quick and often spectacularly colourful cover on temporary soil dumps, temporarily cleared areas and the peripheral areas of construction sites. They are easily established at low cost. The visual impact of a mass of poppies. cornflowers and marigolds distracts public attention from the otherwise unsightly aspects of such sites. Pictures of annual wildflowers sown on landfill and industrial sites can be seen on the 'Wildflower' and the 'Consultancy' pages of the Herbiseed web site: www.herbiseed.com.

They can also be used on landscape projects to provide a quick visual display while the establishment of biennial and perennial plants proceeds at a slower pace. This enables the client to obtain an easily perceptible benefit in the first season after planting.

The most widely used annual wildflower display is produced by sowing a balanced mixture of cornfield wildflowers. These are species which used to make cornfields colourful (but less productive) in the days before the invention of herbicides. As a result of herbicide use, several of these species have become quite rare. The following species are robust and give the greatest visual impact:

For smaller, more formal areas, the following low growing species are appropriate:

The robust annual wildflowers listed above are tolerant of a wide range of soil types, from well consolidated crushed masonry and crushed brick , gravel heaps and weathered chalk to good agricultural soil. On the poorer, dry substrates, poppy and corn cockle will grow best, with corn marigold and corn chamomile dominating on wetter soils. The very dry substrates should be sown in September to ensure plant establishment before the soil dries out in early summer.

Smooth the contours of the site to permit preparation of a seed bed. If weeds are present, spray with glyphosate (eg Roundup). Prepare a fine, firm seedbed with at least 5cm of tilth. Broadcast the seed mixture evenly onto the seedbed at a rate of 20-30 kilos per hectare (8-10 kilos per acre, 2-3 grams per square yard). Use the higher seed rate where there are reasons to anticipate competition from weeds, such as on fertile soils or sites where weeds have seeded in previous seasons. Harrow very lightly and roll the seedbed.

Fertiliser application is positively detrimental on normal soils (it encourages the plants to grow tall and leafy at the expense of early flower production, and encourages weeds). However on rubble, gravel or chalk substrates with no admixture of soil, 200kg. per hectare of an NPK fertiliser immediately after sowing, and for a September sowing, again in the early spring can greatly speed up plant establishment.

The best time for sowing is September to November, but sowings up to the end of April can be successful on soils with adequate water holding capacity. Flowering usually commences in June and continues to September.

Most substrates contain sufficient plant nutrients to support annual wildflowers. On rich soils they will grow to 60cm high, but will be much shorter on nutrient poor or dry soils. Adding fertiliser is positively deleterious on topsoil since it encourages weeds and lush growth at the expense of flowering. However, up to 200 kilos per acre of a 10:10:10 fertiliser is beneficial on pure sand or pure rubble subsoils.

At 20 kilos per hectare and £40 per kilo, seed costs are £800 per hectare or £300 per acre.

Apart from an application of fertiliser in spring, only on the poorest of soils to assist plant establishment, no management is necessary. Depending on the season and on site conditions the wildflowers will commence blooming in June and continue into August. In many cases the site can look as spectacular as the pictures on the ‘Wildflower’ and ‘Consultancy’ pages of the Herbiseed web site. After flowering the plant remains should be cut down.

At the end of the flowering season the plant residues can be chopped and disked into the soil, whereupon a further season’s crop of annual wildflowers will regenerate from the seed of the previous season. However, some topping up with new seed to increase floral diversity might be desirable to increase the frequency of any species which did not do well in the first season.

The second year of an annual wildflower display can better than the first. However, there is a tendency for the area to be invaded by weeds or perennial grasses which increase in frequency in subsequent years. For this reason annual wildflowers can be treated as a visually attractive temporary cover and either undersown with a grass and perennial wildflower mixture or managed by mowing to encourage progression to grassland in subsequent years.

If it is desired to maintain a site in annual wildflowers for several years, cut and remove the dying vegetation in August. Allow any weeds to regrow and spray with glyphosate in late August or the first week of September. Three days after spraying, rotavate or power harrow the area and re sow the annual wildflower seed.

Seed can be obtained from Herbiseed, who will be happy to advise on site and species suitability.

Herbiseed, New Farm, Mire Lane, West End, Twyford, RG10 0NJ, England.
Tel: +44 (0) 1189 349 464  Fax: +44 (0) 1189 241 996  e-mail:[email protected]