How and when should I use wildflower & grass seed mixes?
Weed control is critical to the successful development of wild flower meadows. Deep ploughing, to a depth of 15 to 20 cm, will help bury vegetation and bring less fertile soil to the surface. The ‘stale seed bed’ technique is effective and involves allowing weed seedlings to germinate for some 4 to 6 weeks after seed bed cultivation and then either weeding by hand or by using a systemic herbicide to kill the young weeds. The more often the treatment can be repeated, the fewer residual problems experienced with weeds. Please note, however, that recent research has shown that some herbicides can have a detrimental effect on wildlife and on the health of the person carrying out the spraying, so you may decide to avoid the use of chemicals, even though you would not be repeating this treatment in the future. Soil cultivation normally comprises ploughing and secondary cultivation to create a firm fine tilth using harrows, discs, tined cultivators, rotavator or, on a small scale, a rake.
The optimum time for sowing is late Summer/early Autumn, with April-May the next best window (especially if your soil is clay and it is waterlogged in the Autumn). Sow onto the surface but do not harrow or rake in. Instead use one or two passes from a ribbed roller to firm and level the seed bed and create good seed soil contact, or walk over the site with your feet close together.
What seed and Seed rate should I use?
Seeding rates are normally 3-4 grams per m², but in some circumstances this is raised to 5 grams per m², e.g. on sites considered to be at risk from erosion. On large sites seeding rates can be lowered to as little as 2 grams per m², if clients are prepared to allow a wild flower meadow to develop gradually.
Wild flower seed mixes normally contain 80% non-invasive grasses and 20% wild flowers. Seed cocktails are made up for the important combinations of soil type, pH, and moisture status. Typical habitats catered for are loam, clay, chalky, sandy and wet soils. These seed mixes contain perennial flowers and grasses; they are not to be confused with Cornfield mixtures which contain the colourful annuals (poppy, cornflower, corn marigold etc.) and which are sown at 1-3 grams per m², either in the autumn or the early spring and are short term.
Can I oversow an existing grassland?
Normally this is a recipe for disaster. There is a technique involving cutting the grass very short in the mid summer, dicing the site to create 50% bare earth and then oversowing in the late summer/early autumn, that is claimed to work provided the site is very regularly cut in the first season. This technique is only useful on sites of low fertility. Our own experience of this technique has been only partially successful.
One seed that can be successfully over sown is yellow rattle seed. Yellow rattle is an annual plant that is semi-parasitic on grass. It can control grass growth and is an incredibly valuable plant to establish in grassland as it reduces the need for mowing and improves the viability of other wild flowers. To establish yellow rattle into a sward certain rules have to be followed.
Cut the grass short (3cm), scarify the surface and sow with Yellow Rattle seed by hand on to short grass before Christmas, so that it over winters and vernalises naturally in moist conditions. It does not need to be worked into the soil surface. As a rough guide ½-1 gram/m² will be required. It is important to ensure that the grass is fairly short (maximum 2-5 cm) by the beginning of March so that the seedlings can more easily push up through the sward in early spring.
The grass should not then be cut from early March through at least until the end of July to allow the Yellow Rattle seed to ripen. (Grass which is heavily summer grazed by rabbits will not be appropriate.) It is important that the grass is then cut quite short and the cuttings removed. This will also help spread the Yellow Rattle seed around.