This section is from the book "The Gardener's Monthly And Horticulturist V20", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
In France they are troubled much by May frosts in the vineyards. An article has recently appeared in the Annates des Sciences Naturelles showing that two grape-growers sow the vineyard with rape seed in October, which by May is several feet high. The heat given off by this mass of living vegetation is said to be sufficient to raise the temperature a few degrees, and thus protect the vines from frost. It may also have the effect of shading the ground, and prevent sun warming, thus keeping back growth a little.