How to grow cowpea

Buy certified seed from a registered dealer — a sealed, labelled bag with the variety name and this season's packing date. Clean seed is your cheapest insurance: blight, anthracnose and mosaic virus all travel inside dirty grain.

Choose a variety to match your rains and your plan — a quick (60–70 day) type where rains are short, a medium one where they last; an erect grain type for dry peas, or a spreading type for lots of leaves and pods to eat. Ask the dealer or check your recommendation.

Buy the basal fertiliser your recommendation gives — a phosphorus (P) and potassium (K) compound, such as single superphosphate or a low-nitrogen compound. Do not buy nitrogen top-dressing (urea or AN) the way you would for maize — cowpea makes its own nitrogen, and extra N just grows soft leaf and feeds aphids.

For new land, or a field that has never grown cowpea, groundnut or pigeonpea, ask for Bradyrhizobium inoculant — a small packet of living bacteria that lets the roots fix their own nitrogen. (Those three are cowpea-family legumes that carry the same friendly bacteria, so a field that grew them recently may already have it; a past common bean crop doesn't count, because bean uses a different bacteria.) Keep it cool and shaded, never in the sun or a hot pocket, and use it before its expiry date.

Store seed and fertiliser dry, off the floor, away from food, water and children. Keep the label and receipt in case the seed turns out poor.

In the week or two before you plant, clear weeds and old crop trash off the planting lines so the small seed meets clean, firm soil.

Loosen the soil about 15–20 cm — a spade's depth — so roots go down and water soaks in; cowpea's roots and nodules need air, not a hardpan.

Break the big clods to a fine crumb. Small cowpea seed dropped among big clods sits in air pockets and comes up patchy.

Make sure water can drain away. On flat or heavy land, plant on ridges or low mounds so the plants sit above any standing water. On a slope, work across the slope to catch the rain without waterlogging.

Use only well-rotted manure or compost — dark, crumbly, no strong smell. Skip this altogether on already-fertile land; cowpea needs very little.

Spread it thinly and evenly over the seedbed — a light dressing is plenty; too much rich manure grows leaf instead of pods.

Work it into the topsoil about 1–2 weeks before planting so it settles in with the soil.

Plant into warm, moist soil — warmer than about 21 °C (the season's warm rains, not the first cold shower). Cowpea seed rots in cold, wet ground.

Inoculate where needed (new land, or land that hasn't grown cowpea, groundnut or pigeonpea): tip the Bradyrhizobium powder into a little clean water or thin sugar-water, stir it through the seed until every seed is coated dark, and keep the coated seed in the shade.

Plant the coated seed the same day — the bacteria are alive and die in sun and heat, so don't coat more seed than you'll sow today.

Drop 2 seeds per hill, about one finger-joint deep (2.5–3.8 cm) — a little deeper in dry sand so the seed reaches moisture, shallower in heavy, wet soil.

Space by the plant's habit: for erect grain types, a stride between rows (≈75 cm) and a hand-span between hills (about 25 cm); for spreading types, give them room — about two hand-spans between hills (about 50 cm) — so the vines don't choke each other.

Place the basal P/K — about one bottle-cap per hill — a hand's width (about 5 cm) to the SIDE of the seed and a little below, never touching it, or the fertiliser burns the sprout. Cover and firm the soil so the seed sits snug in moist earth.

Walk the young crop twice a week. Look along the rows for gaps and for seedlings toppling over.

Check the shoot tips and the undersides of the first leaves for black aphid colonies — small, soft, shiny-black insects clustered on the stem, often with sticky honeydew and ants.

Watch for damping-off: seedlings that flop over with a dark, pinched, rotten patch right at the soil line, worst in the damp, crowded spots.

Look for mosaic virus: young leaves mottled light-and-dark green, puckered or curled. Pull out and destroy these plants at once — they are the source the aphids spread from.

Count the gaps (hills with no seedling up) so you know whether to gap-fill in the next few days.

Act at the first aphid colonies — a knock-back with soapy water or neem, or a selective aphicide on a bad patch — before they build up. If a whole patch damps off or the stand is thin → gap-fill or re-sow while the soil is still moist.

About a week after planting, walk the rows and find the hills where nothing came up.

While the soil is still moist and the crop is only a few days old, re-sow 2 fresh seeds (inoculated, if you inoculated the first sowing) into each blank hill.

Firm the soil over them so they sit in moist earth, and water them in if the top is drying.

If it is already two weeks or more since planting → leave the gaps. A seedling started that late stays small and shaded and gives almost nothing; don't waste the seed.

Keep the topsoil just moist until the crop is up and established — moist, not wet. Push a finger in: water when the top few centimetres are dry.

Water little and often on sandy soils that dry fast; less on heavier soils.

Never leave water standing. Cowpea drowns and its root nodules die in a waterlogged field — drain any low spots.

Walk the crop twice a week. Scan the shoot tips and leaf undersides for black aphid colonies and their sticky honeydew.

Look for mosaic virus — mottled, puckered, light-and-dark leaves. Pull and destroy sick plants; don't let them seed the aphids.

Check leaf colour. Healthy cowpea is a deep green. Evenly pale, yellow plants can mean the nodules aren't fixing nitrogen — dig one up to check.

Dig up one plant about 3–4 weeks after planting and look at the roots. Good nodules are round bumps that are pink or red inside when you cut one open — that colour means they are fixing nitrogen.

Watch for Striga (a small witchweed with purple-pink flowers) coming up near the cowpea, and for caterpillars and beetles chewing the young leaves.

Act at the thresholds: knock back aphid patches early, and hand-pull Striga before it flowers. Don't blanket-spray for a few chewed leaves — a healthy plant carries light leaf damage. If the nodules are white, grey or absent → fixation failed: give a light dose of nitrogen to carry the crop, and use fresh inoculant next season.

Weed early — about 2–3 weeks after planting, before the weeds get taller than the cowpea.

Hoe shallowly between and along the rows. Cowpea's feeder roots and nodules sit close to the surface — deep hoeing near the plants cuts them.

Pull out Striga and any climbing weeds by hand, roots and all, before they flower and set seed.

In dry areas, leave the pulled weeds lying between the rows as a light mulch to hold moisture.

Weed again about 5 weeks after planting, before flowering starts.

On spreading types, work carefully — lift the trailing vines aside and hoe shallowly so you don't tear the runners or bury the shoots.

Once the crop closes its canopy and shades the ground, it smothers most new weeds itself — this is usually the last weeding you need.

Walk the crop every 2–3 days through budding and flowering — more often than at any other stage.

Open a few flowers and buds over your palm and tap them. Look for tiny dark slivers that crawl or jump — thrips — and judge roughly how many per flower.

Look for Maruca: flowers and buds webbed together with silk, a small pale caterpillar with dark spots boring inside, and browning buds that won't open.

Check the young shoots for lingering black aphids and their honeydew.

Write down what you find. This is the spray window, so act on it: spray if thrips are building in the flowers or you see the first Maruca webbing (see the spray tasks).

Time it at bud initiation — when the first flower buds appear, just before the flowers open (about 5 days before you expect flowering).

Measure the dose with the cap supplied and mix it into a full knapsack (15–20 L) of clean water — right dose, no guessing.

Spray to wet the buds and flowering shoots without dripping, in the cool of the morning when the flowers are open.

Dress for it: long-sleeved shirt, cover your nose and mouth, spray with the wind behind you, and keep children and animals away.

Respect the pre-harvest interval — wait the number of days on the label before you pick any leaves, green pods or grain. This matters most on cowpea, whose leaves and green pods you eat.

Wash yourself, your clothes and the sprayer afterwards. If Maruca webbing keeps appearing after this spray → rotate to a different chemical group for the next spray rather than repeat the same one.

Time it at about half-flowering — when roughly 1 in 2 plants has open flowers (about a week after Spray 1).

Rotate to a different chemical group from Spray 1 so the pests don't build resistance. Measure with the cap into a full knapsack (15–20 L).

Spray to wet the open flowers and shoots in the cool of the morning, when thrips are active inside the flowers.

Wear long sleeves, cover your nose and mouth, spray with the wind behind you, keep people and animals off, and wash afterwards.

Respect the pre-harvest interval before picking leaves, green pods or grain. If thrips are still heavy in the flowers after this spray → check you sprayed in the morning with flowers open, and rotate the product again.

Keep the soil evenly moist right through budding and flowering — no swings from bone-dry to soaked.

Water every 5–7 days, more often in heat or on sandy soil.

Never let the crop wilt during flowering, even for a day — a check now costs you flowers and pods.

Still don't waterlog it — keep it moist and steady, not flooded.

Walk the crop every 2–3 days through early podding.

Look on and around the young green pods for pod-sucking bugs — bigger brown or green shield- or stick-shaped bugs — and gently shake a plant over your hand to count how many drop.

Count bugs per metre of row. The action point is 2 or more bugs per metre.

Squeeze a few young pods — soft, flat, dimpled spots mean bugs have already fed and the seed inside is shrivelling.

Keep an eye out for Maruca still boring into pods, and for the first pods starting to dry.

If you count 2 or more pod bugs per metre of row → spray (Spray 3). Below that, keep scouting.

Spray at early podding when scouting shows 2 or more pod bugs per metre of row — don't spray on the calendar, spray on the count.

Rotate to a different chemical group again. Measure with the cap into a full knapsack (15–20 L).

Spray to wet the pods and podding shoots in the cool of the morning.

Cover your skin, nose and mouth, spray with the wind behind you, keep people and animals away, and wash afterwards.

Respect the pre-harvest interval — this is the strictest one, because green pods and grain are close to eating. Wait the label's days before you pick or harvest. If bugs return above threshold and you can't meet the interval → stop spraying and harvest the ready pods instead.

Keep watering every 5–7 days while the pods are filling and the leaves are still green.

As the lower pods turn from green to tan and the plant starts to yellow, reduce the water.

Stop watering once most pods are drying, so the grain dries down cleanly. (For a leaf or green-pod crop you keep picking, carry on watering instead — you're not drying grain.)