Green manure promotes green-thumb success

GARDENING

If you're new to gardening, the term "green manure" might conjure up unpleasant images. Though it sounds like a strange animal byproduct or perhaps the newest eco-friendly soil additive, green manure actually relates to a centuries-old agricultural technique that enhances the soil.

Farmers and vegetable gardeners strategically rotate crops after harvest or when soil demonstrates a need for nutrient replenishment. Rather than leaving the land fallow, they plant a "cover crop" of red clover, winter rye, alfalfa or similar plants.

This secondary crop provides numerous benefits while it grows; then, near maturity, it is tilled into the soil as green manure, usually a month before the next planting cycle. The process works just as well in small gardens as large farms.

The time and cost of planting green manure not only are minimal but also far outweighed by the returns. Acting as nature's fertilizer, green manure improves soil health by adding or recycling essential nutrients such as nitrogen, phosphorous and calcium.

Buckwheat, a summer-grown cover crop with an extensive root system, tends to reach more deeply into the earth to absorb other important nutrients - such as potassium - that normally are not within reach of shorter-rooted crops.

Green manure also provides organic matter that later is broken down by microorganisms. Over time, this decomposition releases additional nutrients and makes the soil less compact.

Growing a diversity of crops provides another natural benefit: pest-control management. Different plantings at various times of the year help maintain pest balance and prevent serious outbreaks. Likewise, cover crops attract pollinating insects and provide food for wildlife without seasonal interruption.

During winter, green manure acts as a "living mulch," or protective blanket, that helps prevent soil erosion and retain moisture loss. Since a cover crop competes with weeds for space and light, it helps crowd out unwanted plants by reducing germination and suppressing growth.

As a bonus, a field of red clover or a stand of alfalfa enhances the landscape this time of year.

Green-manure seeds can be purchased in bulk at seed stores or in small quantities at full-service garden centers.

Tom Brinda is assistant executive director for horticulture and education, and Lynn Kirk is public-relations writer at Lewis Ginter Botanical Garden.