Common Name: pen Clover
Trifolium apertum is an erect, usually branched annual plant with few to many stems 20 - 60cm tall, in moist habitats to 100cm[
The plant has been highly recommended as a green manure crop, and is cultivated on a small scale in the northern Caucasus[
Southern Europe - Italy, Greece; W. Asia - Turkey, Caucasus
Scrub, forest margins and glades, in foothills[
]. Among bushes, along forage edges, meadows and glades up to mid-mountain level.
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Species in this genus can generally be grown in a sunny position in a moist but well-drained, circumneutral soil[
This species has a symbiotic relationship with certain soil bacteria; these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[
This species is of outstanding interest for green manure[
]. It has been successfully tried in the northern Caucasus, and small scale cultivations had been reported[
Seed - the seed of Trifolium species is often of two kinds - hard-coated and soft-coated. The soft-coated seeds can germinate immediately, whilst hard-coated seeds remain dormant until the seedcoat has broken down enough to permit the ingress of water. In order to speed up and improve germination rates, hard-coated seeds benefit from scarification before sowing. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing. The seed can usually be sown in spring in situ.
If the seed is in short supply, it might be better to sow it in pots in a cold frame. When they are large enough to handle, prick the seedlings out into individual pots and plant them out after the last expected frosts.