A fast, heat-loving annual grass sown as a summer cover crop to smother weeds, drive roots through tight topsoil, and leave a heavy load of organic matter behind.
Sorghum x drummondii · also called Sudan grass, Sorghum-sudangrass
Windows are counted from the average date of your last spring frost.
One summer sowing shades out weeds in a problem bed, loosens compacted topsoil with dense fibrous roots, and yields several inches of mowed top growth to turn under. Chopped in as a green manure, it has been shown to reduce root-knot nematode numbers.
A little history. A hybrid grass in the sorghum group, bred in the last century for fast summer forage. Its roots and decaying residues release growth-inhibiting compounds that stunt weed seedlings — and vegetable seedlings.
Sow seeds ¾ inch (19 mm) deep, and aim for 3 inches (8 cm) between plants once thinned. Rake seed in shallowly and firm the surface. Keep the top half-inch moist until sprouts show; do not let a crust form. Seedlings emerge in 3–10 days.
Water at sowing, then only during long dry spells. Water when blades roll inward lengthwise during the day. Aim for about 1 inch per week including rain.
Once at sowing; again after the first mowing if regrowth is pale. What to use: about 1 lb of 10–10-10 per 100 sq ft, or a thin layer of composted manure.
Mow at 3–4 ft tall, cutting back to 6–8 inches. Mowing forces tillering (new shoots from the base) and a second flush of roots. Never let seed heads ripen.
It's ready when stand reaches 3–4 ft with a few seed heads just starting to push from the whorls — mow before any head ripens. Cut the stand to 6–8 inches with a string trimmer, scythe, or mower set high. Chop long stems into 6-inch lengths so they break down, then leave them on the surface or turn them in shallowly.
Not stored. Use the cut top growth immediately as surface mulch or shallow-turned green manure.
Expect two or three mowings from one summer sowing rather than a second sowing; regrowth after each cut is fast in warm weather.
Cowpea
The standard summer mix partner: the grass supplies bulk and weed cover while cowpea banks nitrogen in its roots, released mostly the following season as those roots break down. Sow both at the same depth on the same day.
Tomato
A full summer of this grass mowed and turned into a bed has been shown to reduce root-knot nematode numbers, which pays off in tomato ground the next season. Grow it as the preceding cover, never beside standing tomatoes.
Strawberry
Used as a summer cover before new strawberry beds, it often reduces nematode and soilborne rot pressure in ground that has carried berries before. Turn residue in and wait about 3 weeks before setting plants.
Radish
In a late-summer cover mix, the grass fills the top few inches with fine roots while radish drives a thick taproot through compacted layers below. They can share the same bed without fighting for the same water.
Cantaloupe
A standing strip of this grass on the windward side can shelter young melon vines from drying wind and blowing sand. Keep the strip at least 3 ft clear of the vines so it does not shade them or drink their water.
Living roots and decaying residues of this grass release compounds that stunt germinating seeds and young seedlings, and the stand out-competes anything shorter for light and water. Grow it as a stand-alone summer cover, then allow about 3 weeks after turning residue in before sowing the next crop.
Sorghum
Both are sorghum-group grasses hosting the same leaf diseases and sap-feeding aphids, so side-by-side plantings stack the pressure on each other. Keep them in separate beds and respect the 2-year gap between grass and grain crops.
Pearl Millet
Two tall, fast summer grasses in one bed simply race each other for water, nitrogen, and light, and neither gains cover. They also share grass pests, so grow one or the other in a given season.
Lettuce
Lettuce seed is the classic test case for this grass: extracts of its residue measurably cut lettuce germination and shrink the first roots. Do not sow lettuce into fresh residue, and wait 3-4 weeks after incorporation.
Carrot
Small-seeded, slow-starting root crops often come up thin and stunted in beds where this grass was recently turned under. Give the bed a full month, or sow a transplanted crop first instead.
Give grasses and grains 2 years away from this spot before any of its relatives return.
The pea and bean family, the squash family or the tomato family thrive in this ground next season.
A giver: it leaves little nitrogen but a large volume of roots and stems that build soil structure and organic matter. Keep other grasses and grains out of the bed for 2 years, and follow it with beans or peas, the squash family, or the tomato family — waiting about 3 weeks after turning residue in.
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