As we are harvesting Yellow Rattle Rhinanthus minor seed it seemed like a good time to write about it. Yellow Rattle, or Hay Rattle, or Cockscomb, is an attractive yellow annual wildflower of meadows. There seem to be at least 6 different subspecies of it in the UK, which makes its appearance variable. Rattle is widely distributed across the country, however. It’s a good bumblebee and butterfly plant, flowering in June. Its seed rattles in the wind, traditionally telling farmers it was the time to make hay. Farmers, however, don’t like to see it.
Yellow Rattle gets some of its nutrients from surrounding plants, particularly grasses. As a hemi-parasite it was regarded as a pest by farmers, as it could reduce hay yields by up to 50%. It doesn’t make the grass look sick, but just enfeebles it. It’s less thick and shorter. This provides obvious benefits if you’re trying to establish a wildflower meadow, particularly in an existing sward or on a site with medium soil fertility. This can be tricky, even with retiring meadow grasses. It will give the wildflowers a much better chance. They will have more sun, more water and less competition generally.
Rattle seed needs to go through a prolonged period of cold before it will germinate, so must be sown in autumn or early winter. It has a limited shelf life, so seed from the current harvest is best sown this year. This trait in an annual means that it’s very easy to get rid of it; just mow in May/June before it sets seed. This is why it is so much less common than it used to be in grassland. If you sow a general meadow mix in spring which includes Rattle, it’s worth buying extra in the autumn to add to it.
We recommend a sowing rate for Yellow Rattle of between 0.5 and 1g per square metre, and will sell you seed down to 250g, or smaller quantities down to 20g through our sister website www.BritishWildflowerMeadowSeeds.co.uk. If you don’t buy the seed through us do make sure you source it from another reputable seller. One of the reasons it’s expensive is that it’s difficult to process and, consequently, its germination rates can vary enormously.
As Rhinanthus parasitises grass, sow it with grass seed or into an existing sward; don’t try to establish it in a seed tray. After sowing, lightly roll or tread the seed in to ensure good contact with the soil. Yellow Rattle seeds are light and wind born, so this is particularly important.
If your site has existing grass it is important that you scarify or chain harrow, and then cut or grazed as short as possible before sowing the Rattle. Keep grazing or cutting to below 2cm throughout the winter (sheep are best for the job) after sowing, and throughout winters thereafter. The seedlings start growing in early spring, so make sure you don’t chop their heads off!
If you are using Rattle as the first step towards establishing a wildflower meadow from an existing sward, add plug plants or seed to the site in the second year. Your chances of success will vary according to which grasses you have and how fertile the soil is. You may well find wildflowers already in the grass, which show themselves with your new regime.
It’s really important to cut or graze your meadow area every year from late summer to March. Be careful not to chop the Yellow Rattle seedlings’ heads off as they emerge, though!