A living mulch is a cover crop interplanted or undersown with a main crop to serve the functions of a mulch, such as weed suppression and regulation of soil temperature. For example, some gardeners plant white clover beneath young squash or corn. Late-season brassica (broccoli, cauliflower, etc.) plantings may be underseeded with a winter-hardy cover crop, such as hairy vetch. Dense, low-growing ground covers, such as purslane, can be good living mulches for taller crops, such as broccoli.
Living mulches offer several advantages:
1. Reduced weed competition
2. Additional organic matter and, if nitrogen-fixing plants are used as mulch, nitrogen
3. Reduced soil erosion
4. Increased water infiltration through channels developed by root growth
5. Reduced soil compaction
6. Greater biodiversity
Living mulches also have a drawback: They compete with the main crop for water. Living mulches usually reduce yields in dry years, unless gardens are watered often.
With a killed mulch system, a winter cover crop such as wheat or rye is planted in the fall and allowed to grow during the fall and winter. These cover crops prevent soil erosion and form a dense canopy that prevents emergence and/or growth of many common weed species. The cover crop is allowed to grow to its full vegetative height and then killed by cutting before seed head emergence. The resulting residue is distributed to form a dense, uniform mulch. Some cover crops prevent weed emergence while growing, and after they have been killed, by releasing chemical compounds into the soil that inhibit weed germination (a process called allelopathy). Large-seeded species such as snap beans, peas, and corn, and transplanted species such as pepper, tomato, broccoli, cabbage, and cauliflower can be grown successfully in a killed mulch system.
