Yellow Rattle, Rhinanthus minor
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 very variable. Rattle is widely distributed across the country, however. It's a good bumblebee and butterfly plant, flowering in June then rattling in the wind, traditionally telling you it was the time to make hay. Farmers, however, don't like to see it.
Yellow Rattle in Meadow Creation
Yellow Rattle gets some of its nutrients from surrounding plants, particularly grasses*. As a hemi-parasite farmers regarded it as an unwelcome weed. It can reduce hay yields by up to 50%. Eyebright (Euphrasia) does a similar thing. Rattle 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. That's particularly so in an existing sward or on a site with medium soil fertility. This can be tricky, even with retiring meadow grasses. Adding Yellow Rattle will give the wildflowers a much better chance. They will have more sun, more water and less competition generally. Further, once the Rhinanthus plants have died back - which as annuals they do in late summer - they leave gaps for other wildflowers.
Yellow Rattle is generally included in generic wildflower meadow seed mixes, and can be a large component of "direct harvest" mixes. These are mixes taken from donor meadows and cleaned up before sale. They often represent great value for money and offer super diversity.
Rattle seed needs to go through a prolonged period of cold before it will germinate - vernalisation - so must be sown from summer to early winter. Some say it has to be sown in August as soon as the plants naturally set seed, but there's no scientific evidence for that. Sow before Christmas seems the best advice. If Rhinanthus is part of a general seed mix, best to sow in late summer or autumn.
Yellow Rattle has a limited shelf life, so seed from the current harvest is best sown in the same 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.
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 stop cutting / grazing in March. You don't want to chop their heads off or give a tasty snack to a sheep!
Yellow Rattle Seed
We recommend a sowing rate for Rhinanthus of between 0.5 and 1g per square metre. We can sell you seed down to 250g, or smaller quantities down to 20g through our sister website www.BritishWildflowerMeadowSeeds.co.uk. We try to source seed with different provenance, to try to partly reflect the regional variations in the plant. If you don't buy the seed through us do make sure you source it from another reputable seller.
It's not cheap. One of the reasons it's expensive is that it's difficult to process and, consequently, its germination rates can vary enormously. As we've said, it also has a limited shelf life, and shouldn't generally be supplied or used 6 months after harvest. This means we run our stocks down to zero.
The good news is that it only needs to be sown at 0.5g - 1g per square metre if sown on its own. Meadow mixes which include it are typically sown at 4g per square metre.
As Rhinanthus parasitizes 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 you are using Rattle as the first step towards establishing a wildflower meadow from an existing sward, add plug plants or wildflower 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. Many lawn and agricultural grass mixes include a large element of perennial rye grass, Lolium perenne, which makes things difficult. It's a thug. If you're lucky though 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. Rhinanthus seedlings need short grassland in the late winter to compete. Be careful not to chop the Yellow Rattle seedlings' heads off as they emerge, though!
*Interestingly some plants, like Oxeye daisy or Ribwort plantain, have developed strategies to resist Rattle, which means they do well in swards where there's a lot of it...