Using yellow rattle to increase species diversity
Yellow Rattle is the key to success with any wild flower meadow or area of grass. It is an attractive, semi-parasitic, grassland annual. In the past this plant was a serious problem for farmers as it weakens grasses and as a result can reduce hay yields by as much as 50%. In a landscape or garden context however, this suppression of grass growth is welcomed as it produces a better display of wild flowers and eases the mowing required!
Yellow rattle germinates late February to early March, flowers in June, and sets seed in July. At the end of each growing season as the annual yellow rattle plants die away they leave behind gaps into which new wild flowers can establish. As a result, wild flower seed sown into an existing sward will establish more readily in areas where yellow rattle already does well.
Getting yellow rattle started
Yellow rattle establishment can be tricky and plant numbers may take two to three years to build up, this will depend upon the sowing rate chosen, and site conditions.
Top tips for good results
- Yellow rattle will not thrive in all grassland. Areas that are overgrown by coarse or vigorous grass (ryegrass, cocksfoot, tall oat-grass or couch), may be tricky. Grassland that is the result of sowing a meadow mixture should have suitable finer grasses, as will finer turf in gardens and meadows.
- Cut ( or graze if you have some sheep!) the sward in the autumn, aim to keep the grass short (40-50mm). Graze or mow before and after seeding as needed.
- Create gaps across the site with exposed soil for yellow rattle seed to germinate in. This can be achieved by autumn/winter grazing with stock (their hooves open the sward), or mechanically by harrowing or raking, aiming to expose up to 50% bare soil.
- Timing: Sow in the Autumn as it needs prolonged chilling through the winter to trigger its germination the following spring.
- Sowing rate: yellow rattle seed should be scattered onto the prepared surface at a rate of 0.1 to 1 g/m2.
Yellow rattle may be sown as a component of a meadow mixtures on to a prepared seedbed. To be sure of getting yellow rattle in the second year, it is best to re-sow yellow rattle in the autumn of the first year (as above). Where cornfield annuals have been sown as a ‘nurse crop', yellow rattle has more opportunity to self-seed.
Aftercare: Managing swards for yellow rattle
Yellow rattle is an annual with short lived seed which needs a chance to set seed each year. Therefore don't cut before late July/early August to allow seed to be set and scattered.
Autumn grazing, or mowing and harrowing, is also important each year as it will help to keep the sward open. This is important in providing new sites in to which yellow rattle can establish the following spring.
If you find that your yellow rattle is overtaking - you can mow early in the season ( May/June) to prevent seeding for one season.