Yellow rattle is a pretty but otherwise inconspicuous flower that grows in grasslands. Beneath the soil, it harbours a dark secret however – it is a plant vampire, attaching to the roots of other plants and leeching away their nutrients. Far from being a villain, it has an important role to play in maintaining the competitive balance between grasses and other plants, and can be a useful tool in establishing a more diverse wildflower meadow.

Yellow rattle (Latin: Rhinanthus minor) is an annual flowering plant species, meaning it completes its life cycle in a year. It grows in meadows and grasslands, growing up to 45cm in height, and producing bright yellow flowers. When the plant produces seeds, they are held loosely in brown seed pods, and can be heard “rattling” around if the plant is shaken (hence the common name).

Yellow rattle is a hemiparasite – this means it steals water and nutrients from other plants, but also produces some of its own food through photosynthesis. Other plants in its family are holoparasites – they are totally dependent on their hosts for food, and so don’t photosynthesise. These plants are not green as a result, because they lack the green chlorophyll that plants use in photosynthesis. Yellow rattle attaches to its host plants via their roots. It produces growths on its own roots called haustoria which attach to the roots of the host. It then diverts water and nutrients from the host plant to its own roots. It particularly likes to parasitise grasses, and this is where yellow rattle becomes a useful tool in promoting biodiversity.

Semi-natural grasslands are grasslands which have been created and managed by humans, though without the addition of nutrients to soil to improve its fertility. Lower soil fertility is a good thing for plant biodiversity – in grasslands with high levels of fertility, a small number of very competitive and rapidly growing species take over, excluding many other less competitive species. When nutrients are restricted, these species cannot gain such a strong foothold in the area, and other species have a chance to establish. This further promotes biodiversity by attracting a wider range of invertebrates and the animals that prey upon them. Sadly, semi-natural grasslands are in danger due to conversion to arable farmland, and addition of nutrients to soil – grasslands that could be species-rich meadows are instead becoming dominated by just a few coarse grass species.

Yellow rattle is one of the tools in the fight against the disappearance of semi-natural grasslands. As a parasite, it weakens grasses by siphoning away water and nutrients for its own use. This means the host plants cannot grow as quickly and may produce less seed or produce it more slowly. In this way, yellow rattle slows the expansion of these grasses, and allows room for other species to begin growing in the area. If you want to help establish a diverse wildflower meadow, you can sow yellow rattle for yourself – it is native to Ireland and its seed can be gotten easily online.

Here’s a few tips to getting yellow rattle established in your patch:

1. Source the seed from either a specialist supplier who can tell you the seed has been harvested in the last year, or from a place where yellow rattle is growing and setting seed – you want the freshest seed possible!
2. Cut the grass as short as you can between July and September, and remove the thatch (a layer of dead grass and moss that builds up on the soil surface) – this will expose bare soil that you can sow your yellow rattle seed on
3. Sow your seed by November! Yellow rattle seeds need a few months of cold weather to begin growing in the following spring (this is called vernalisation)
4. Once your yellow rattle has grown up and set seed, cut the meadow down hard, preferably in August or September, and remove the clippings. This keeps the grasses at bay until more yellow rattle has had a chance to grow, and allows later bloomers to provide their benefits as long into the year as possible before cutting
5. If you have livestock, allow them to graze up until the New Year in the area where your yellow rattle has set seed. In a garden, simply cut the grass once or twice before the end of the year, removing the clippings.

Written by Tom Murphy

References:

https://www.wildlifetrusts.org/wildlife-explorer/wildflowers/yellow-rattle

https://www.plantlife.org.uk/uk/discover-wild-plants-nature/how-to-grow-yellow-rattle-rhinanthus-minor

Ridding, L.E., Redhead, J.W. & Pywell, R.F. (2015): Fate of semi-natural grassland in England between 1960 and 2013: a test of national conservation policy. Global Ecology and Conservation, 4, pp.516 – 525. DOI: 10.1016/j.gecco.2015.10.004

Janssens, F., Peeters, A., Tallowin, J.R.B., Bakker, J.P., Bekker, R.M., Fillat, F. & Oomes, M.J.M. (1998): Relationship between soil chemical factors and grassland diversity. Plant and Soil, 202, pp. pp. 69 – 78. DOI: 10.1023/A:1004389614865

Pywell, R.F., Bullock, J.M., Walker, K.J., Coulson, S.J., Gregory, S.J. & Stevenson, M.J. (2004): Facilitating grassland diversification using the hemiparasitic plant Rhinanthus minor. Journal of Applied Ecology, 41, pp. 880 – 887. DOI: 10.1111/j.0021-8901.2004.00940.x