How to Grow Buckwheat Cover Crops in Australia

Buckwheat (Fagopyrum esculentum, family Polygonaceae) is a fast, frost-tender annual grown as a summer cover crop. Closer kin to rhubarb than to wheat, it shades out weeds within weeks, copes with poor soil and fills with small white flowers for bees. The usual slip is the cutting: too early and it regrows, too late and it seeds itself through the next crop.

Three mistakes that matter

1. Sowing before the frosts are over. A single light frost kills buckwheat, and seed sown into cold, wet soil sits and rots. Wait for the cue When to plant gives, then sow into warm, moist soil for a quick, even start.
2. Sowing thin or patchy. Weeds grow up through any gap wider than about 25 cm, which undoes the reason for sowing it. Scatter the full rate evenly over a fine, firm bed, as Sowing Seeds describes.
3. Cutting at the wrong moment. Mown before the patch is well in flower, it can regrow from the lower stems. Left until seeds turn brown, it drops them through the next crop. Cutting and Digging In gives the window.

When to plant

Sow after the last frost, into soil of 13°C or more for a quick start, and stop about eight weeks before the first autumn frost. Each sowing is ready to cut in five to eight weeks, so a long summer fits two or three crops in a row.

In hot, dry weather, water the bed a few days before sowing so the seed lands in moist soil. Hold off if heavy rain is forecast, because the seed rots in soil that stays saturated even for a few hours.

Site, soil and setup

Choose an open bed that is resting between crops, or a patch of tired or newly cleared ground. The fine roots need loose, crumbly soil, so heavy clay that stays wet is a poor choice.

Sowing Seeds

Sow Green Manure Buckwheat seeds straight into the bed: the seed is large and quick to come up, so no tray is needed.

Sowing direct

• Rake the bed to a fine, firm surface, clear of clods and weeds.
• Scatter 7 to 8 g of seed per square metre, enough to cover the thinner spots.
• Rake the seed in 10 to 25 mm deep; seed buried deeper than about 40 mm comes up poorly and unevenly.
• Water in gently and keep the surface moist until seedlings appear.
• Lay shade cloth over the bed if birds take the seed, and lift it once seedlings are up.
• Expect seedlings in 3 to 5 days in warm soil, or up to 10 days in cooler soil.

Sown in rows 15 to 20 cm apart, about 5 g per square metre is enough, so 500 g covers 100 square metres. Scattering takes more seed but is quicker.

Care by growth stage

Moisture in the first month decides the crop, because buckwheat is not drought tolerant. Most garden soils need no feeding.

On very poor sand where growth stalls, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched in at sowing can help. Where water beads on dry, sandy soil, a wetting agent at the label rate helps it soak in.

Companion planting

Buckwheat earns a place near summer vegetables for its flowers, but it smothers anything slow that shares its bed.

Grows well with

• Pumpkins, zucchini and other summer crops, where a flowering strip nearby draws hoverflies, predatory wasps and ladybirds that attack aphids and mites.
• Strawberries, sown on the bed a summer ahead of planting to cut down weeds before the runners go in.
• Autumn vegetables sown after it, which go into the loose, weed-suppressed soil it leaves behind.

Keep apart

• Slower cover crops such as lablab in the same sowing, because buckwheat is ready weeks earlier and seeds itself if left for the others.
• Small, slow vegetable seedlings in the same bed, which its quick, dense canopy shades out.

Cutting and Digging In

Cut when the patch has just turned white with flowers, usually 5 to 8 weeks after sowing. By then the first flowers are 7 to 10 days old. If seeds have begun to form, cut and dig in the same day, because seed on cut stems can still ripen.

• Cut low with a mower, a whipper snipper or shears.
• Chop the tops, so they break down faster.
• Fork them lightly into the topsoil, or leave them on the surface as mulch.
• Wait 4 to 6 weeks before sowing seed into a dug-in bed, or plant seedlings through surface mulch sooner.
• Pull any stems that survive the cut or regrow, and hoe out later seedlings while small.

Keep leftover seed in a sealed jar somewhere cool and dry. Germination can fall quickly in storage, so test older seed on damp paper towel before sowing a bed.

Weed lists, state by state

Buckwheat has naturalised in New South Wales and Western Australia, and the Queensland and Victorian records are doubtful. No state or territory declares it a weed, and Western Australia lists it as permitted. Its earliest seed can drop before flowering ends, so cutting on time keeps it in the bed.

Common problems

Gaps in the stand. Heavy rain soon after sowing, a crusted surface or seed sown too deep can leave bare patches (see Three mistakes that matter). Resow the gaps once the soil is moist but not soggy.

Wilting on hot afternoons. This is normal, and plants usually perk up overnight. If they are still limp the next morning, the soil is dry: water deeply.

Tall stems falling over. Too much nitrogen or a very dense sowing makes stems spindly, and wind or heavy rain lays them flat. Skip the feeding and cut on time.

Weeds breaking through. A slow start in cool or wet weather gives weeds the lead, and so does extra nitrogen. Pull them early, and wait for warm soil next time. Read more

Pests and diseases

Buckwheat has few pests or diseases in Australia, and most trouble comes while the seedlings are small.

Rutherglen bug (Nysius vinitor). Mottled grey-brown bugs 3 to 4 mm long that breed on weeds and move into crops in large numbers as the weeds dry off. Read more

Cutworms (Agrotis species). Dark, hairless caterpillars up to 50 mm long that hide in the soil by day and cut seedlings off at ground level at night. Scratch the soil beside a felled seedling to find and remove them. Read more

Damping off (Pythium species and Rhizoctonia solani). Soil-borne pathogens rot seed before it emerges, or leave a sunken, water-soaked mark at ground level so seedlings fall over. Wet soil and cold weather make it worse. Read more

Prevention first

• Clear weeds in and around the bed 3 to 4 weeks before sowing.
• Sow into warm, free-draining soil, so seedlings race away.
• Check the bed every few days for the first three weeks for cut or collapsed seedlings.
• Avoid overwatering, and water in the morning so the surface dries by night.

Tips

1. For bees, sow a new strip every week to ten days, so one is coming into flower as the last is cut.
2. If the bed had bought manure, straw or compost, sow a few seeds in a pot of its soil first. Buckwheat is sensitive to herbicide residue, and stunted seedlings give it away.
3. Keep grazing stock off the crop: eating buckwheat can cause photosensitisation (skin damage in bright sunlight).
4. Follow it quickly with the next crop or a winter cover crop. The soft stems break down fast and leave loose soil open to erosion.
5. To grow buckwheat for its tender shoots in the kitchen, see Buckwheat Greens.

Due to quarantine restrictions and our shipping policy, we cannot send Green Manure Buckwheat seeds to Tasmania. Western Australian orders are limited to 10 kg.