What about that yellow rattle?
Last autumn we had prepared our stale seedbed well in advance of the proposed sowing date for the meadow, the final deadline that we set ourselves being the 15th October 2012. We lived daily in hope that a damp, sun-warmed seedbed would be perfectly receptive for the precious and expensive seed mix. Hah!
The heavens opened and the tap stayed on for weeks; the seedbed was then neither sun-warmed nor receptive. It was inundated, stayed inundated all winter, and it was the beginning of May before conditions for sowing came good again. The whole 10ha. of meadow germinated well, was glorious throughout summer, and most of us were thrilled by the shimmer of pollinators above the nurse crop of cornfield annuals.
Last week I completed the first vegetative survey. Almost everything sown had come up, including the now sturdy rosettes of nearly 30 species of meadow perennials and 9 of fine grasses. No yellow rattle, Rhinanthus minor, nor common eyebright, Euphrasia rostkoviana, though.
I wondered whether the rattle seed had become cottered up in the Opico air seeder; they were significantly larger than most of the other species. More likely, however, is lack of exposure to cold. The seed of the annual yellow rattle needs a period of winter cold in order to germinate. There’s probably little hope of the rattle seed that was in the original mix germinating next spring, since it is has a short shelf life (viability) and will have rotted by now.
Hence, the re-sowing this coming Saturday 26th October with our splendid volunteers. Having made all the mistakes that guarantee failure since yellow rattle first became a must-have in meadows, I’m pretty confident that we can crack it this time.
Firstly we will be using seed from this season’s harvest. It ripens mid- to late July, about the time of the traditional hay harvest, and when fully ripe the seeds rattle in the pods (much to the delight of my daughter when she was small). That also gives it its other common name of Hay rattle.
Secondly, this time we’ll ensure that it’s all in before the onset of winter cold.
Thirdly, we’ve cut the sward to about 2.5cm (1in) and will be casting the seed, at about 1g/m2, onto soil ruffled by raking, and firming it in.
The devil, however, is in the detail. The seed needs to hit bare soil to germinate. Since it’s a relatively large, flattened disc shape, it has a tendency to lodge in leaves of grass, even if only an inch high. Yellow rattle needs a grassy host close enough to attach itself to upon germination. The shorter the distance between the host and the yellow rattle, the more successful the establishment, and it does best if it makes a connection early in the season. It’s what’s known as a hemi-parasite and exploits grasses as a supplementary food source. That’s why it’s used to reduce the vigour of grasses in a new meadow, especially one like ours, on formerly arable land, where fertility is likely to favour more robust grasses such as Yorkshire fog, Holcus lanatus, or rye grass, Lolium perenne.
Solution? Aim the seed at areas of bare soil next to the problem grasses; there’ll be plenty of bare patches as we just so happen to have spot-sprayed docks, thistles and problem grasses with malice aforethought.
It has become my custom (and pleasure) to check out a plant’s family relatives when seeking clues as to what might help it thrive – families often share a whole raft of resemblances in cultural needs. And what a weird bunch the yellow rattle’s relatives are. The broomrape family (Orobanchaceae) includes true parasites such as the fleshy, pale and slightly sinister toothwort, Lathraea squamaria, parasitic on the roots of beech, elm, alder and hazel, and Lathraea clandestina, the purple toothwort, a familiar denizen of many old gardens, which prefers alder, willow, and poplar as a host. How interesting it will be to introduce them to our trees, when they’re a bit bigger.
The hemiparasites, which do have chlorophyll and roots of their own, include red bartsia, Odontites verna, a meadow native that parasitizes grasses, and, what do you know … common eyebright, Euphrasia rostkoviana. The last is parasitic on grasses, but also it appears is fairly catholic in its taste for hosts. In either case, I’m betting both of these would succeed with the same treatment as yellow rattle.