Wildflowers are not plants that can survive in any rough patch of land and compete with robust weeds. In fact the opposite is true. Many wild flowers are becoming rare because they have precise growing requirements which are much more difficult to satisfy than those of common weeds. Poor management of weed growth before and after planting is a common cause of unsatisfactory wildflower establishment.

Land on which wildflowers are to be sown needs care and preparation to ensure their survival. This means preparing a soil or subsoil which is adequately drained, can supply adequate air, water and nutrients to plant roots and is free of weeds.

Poorly drained or compacted soils are acceptable only where there is an adequate supply of moisture throughout the summer to support the growth of wetland species and a wetland is the desired end use of the area. Non-wetland species will drown in winter on poorly drained sites, whereas wetland species will die if the site becomes dry in summer. Except on true wetland sites, adequate soil aeration is a necessity. This is because plant roots need oxygen and die in its absence. Agricultural land is normally well aerated, but reclamation sites and urban areas have often been compacted by heavy vehicles. This compaction needs to be alleviated by deep ripping or subsoiling.

Most agricultural soils have adequate or even excessive levels of nutrients to establish grass and wildflower mixtures. Excessive levels of nutrient can promote the growth of weeds and grass more rapidly than that of the wildflowers and are thus undesirable. There is therefore a justification for stripping all but a few centimetres of topsoil from rich farmland if the objective is to establish a low-maintenance wildflower meadow.

Very sandy soils and most subsoils are frequently deficient in nutrients, particularly phosphate (P) and nitrogen (N). Potash (K) tends to be limiting only on inland sands and gravels. This can be an advantage in favouring the growth of wildflowers, which are better adapted to low levels of nutrient than many grasses and weeds. However, extreme nutrient deficiency retards the initial establishment of wild flower and grass seedlings.

Thus application of moderate levels of N, P and K at seed sowing can be advantageous to plant establishment on very poor subsoils provided the substrate is free of weed seeds. Particularly on pure sand, gravel or chalk, a top up of nitrogen may be necessary a few months after sowing to ensure good plant establishment. (Herbiseed is aware that this recommendation is contrary to popular writings on wildflower establishment. Our recommendation is derived from our own practical experience, and is restricted to sowing wildflowers on subsoils where effective weed management has ensured that the substrate is essentially free of weed seeds).

Effective weed management both before and after wildflower sowing is of crucial importance to the success of establishing wildflower grassland. Whatever is the substrate (soil or subsoil) into which the wildflowers are to be planted, it must be essentially free of weed seeds. There is no practical means, chemical or physical, of removing weeds from a grass and wildflower mixture after sowing. Thus, no weeds must be permitted to flower on or near the substrate which is to be used for wildflower sowing during the seasons preceding the landscaping phase of a project. If this golden rule has not been followed, weed seeds must be removed from the soil before wildflowers are sown.

The methods of weed control used prior to sowing must be appropriate to the types of weeds present.

Almost all top soils have a large seed bank of dormant seeds, which readily germinate when conditions are right. Every time the soil is cultivated, new seeds are brought to the surface and eventually germinate. The best means of reducing the annual weed seed population is to fallow the land. This entails preparing a fine, firm seed bed and cultivating it to a depth of 50 mm each time a flush of green seedlings develops. This is most effective in warm damp weather and where irrigation can be applied in dry weather.

The final flush of weeds to occur before sowing is then killed with a foliar spray of a rapidly inactivated herbicide such as paraquat, glyphosate or gluphosinate. Then sow the wildflower seed without further cultivation to avoid bringing more weed seeds to the surface.

These are often present in derelict land, abandoned fields and old pasture, particularly pony paddocks. Their extensive root systems often require repeated applications of herbicide to eliminate them.

Identify the species present and select the appropriate foliar applied systemic herbicide to use. Glyphosate is best for grass control and has some effect on other perennials. It has no soil residual effect and is therefore safe to wildflowers sown subsequently. It can be used up to one day before sowing. ‘Shield’ is best for thistles but can kill some wildflowers (Compositae and Leguminosae) sown several months after application. Asulam is highly effective against docks but can have a soil residual effect. Hormones such as 2, 4-D and CMPP are adequate for thistles and docks and are good on nettles. Do not use any sulphonylurea, imidazolinone or picloram herbicide where wildflowers are to be sown within 12 months of application.

Where both grasses and perennial dicotyledons occur extensively, spray glyphosate first then the dicotyledon herbicide several days later. This is because glyphosate is antagonised by most other herbicides.

When applying any herbicide, spray the foliage thoroughly, but not to the point where the liquid runs off onto the soil. Glyphosate is the only systemic herbicide which can safely be sprayed over more than 10 per cent of an area less than two months before sowing. If perennial dicotyledons occupy more than 10 per cent of the area, they must be controlled with two applications of systemic herbicide spaced over six weeks and sowing delayed for at least two months.

If a wildflower mixture is to be successfully established, adequate time must be available to achieve complete weed control before the planned sowing date. Similarly, this time must be fully utilised by assiduous application of weed control measures.

The following steps are recommended:

1 Visit the site with a BASIS certified agronomist.

· Determine what weeds are present

· Assess the extent of perennial weeds and the weed seed bank

· Plan necessary weed control measures

· Determine probable sowing date from weed control and climatic constraints - not solely from a date in an engineer’s contract!

2 Where perennials are present, commence with perennial weed control sprays. In general, couch grass can be controlled by a single glyphosate application, nettles by one or two hormone sprays, creeping thistle by three sprays. Docks are best sprayed with asulam, rotovated a month later and the regrowth from the chopped roots resprayed, possibly with a less residual hormone herbicide.

3 Do not cultivate until several days after the perennials have been sprayed, since cultivation breaks up parts of the root system which are not then reached by foliar applied systemic herbicides.

4 Subsoil, and cultivate as necessary.

5 Wait for weed seeds to germinate, irrigating if possible during dry periods to encourage germination. Then cultivate to no more than 50 mm to kill the weed seedlings.

6 Repeat as often as necessary until no further weeds germinate under warm, consistently moist conditions.

7 When eventually only a sparse weed flush occurs even under warm, consistently moist conditions, spray these weeds with paraquat, glyphosate or gluphosinate.

8 Sow at least one day later without further cultivation.

9 Harrow ensuring that the soil is not disturbed more than 10 mm deep.

10 Roll, except for autumn and winter sowings on soils which are liable to cap (fine sands and all clays).

On most soils, wildflower mixtures are best sown in early September, but can be successful if sown up to April. Sowings in late spring and summer are dependent upon adequate rainfall for at least a month after germination, so can be a gamble.

Heavy clay is the one soil type on which a spring sowing has a better chance of success than sowing in autumn. It is difficult to break down into an adequately fine seed bed in autumn, and then tends to slump and cap in the winter rains. It is best treated by levelling and cultivating during dry conditions in summer to produce a surface of fist sized clods. These break up in winter frosts and can be harrowed into a good seed bed in spring. This seed bed should not be worked too fine or it will cap before the seedlings emerge.

Suitable seed mixtures are usually based around slow-growing grasses to achieve low maintenance requirements, and wildflowers suitable for the soil type and other site conditions. These aspects are dealt with in Herbiseed Brief Wild Flower Guides No. 3 and 4. Ideally, discuss your project with Herbiseed at the planning stage to ensure that the client’s objectives are best met by integrating site conditions with suitable plant species included in the seed mixture.

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]