Green Manure Buckwheat Is A Fast Growing Short-term Summer Green Manure For Poor Soils. Grows Extremely Fast, Forming A Dense Canopy Of Foliage That Smothers Weeds & Produces Large Amounts Of Organic Matter.a Good Source Of Calcium, Its Long Roots Extract Nutrients From Deep In The Soil. When Left To Flower It Attracts Hoverflies Whose Larvae Feed On Aphids.sow May-august.