Yellow rattle is a grassland annual with yellow, two lipped flowers, the upper lip with two white or purple teeth. Behind the flower the joined sepals inflate to form a green bladder sometimes tinged with red.
Flowering occurs from May through to September followed by a seed capsule which rattles within the now brown and papery bladder. The majority of seed ripens in mid to late July and the rattling of the fruit within the bladder was said to indicate that the meadow was ready to be cut for hay, hence its other common name of hay rattle.
Yellow rattle seed must be sown in autumn as it needs a prolonged period of chilling through the winter to trigger its germination the following spring. Prepare for sowing by cutting the grass very short (25mm) or by grazing very hard and open up sites for germination by harrowing or raking aiming to create up to 50% bare soil.
Broadcast the seed on to the prepared surface. Traditional meadow management based around a late July hay cut provides Yellow rattle the best opportunity to set seed, and for its seed to scatter during the process of haymaking.
Sowing rate: yellow rattle seed should be scattered onto the prepared surface at a rate of 0.1 to 1 g/m2.