How to grow watermelon

Pick a field that has not grown watermelon, melon, cucumber, pumpkin, squash or gourd for at least 5 years — they are all in the melon family (called cucurbits) and all feed the same wilt.

Good crops to have grown there in between are cereals (maize, sorghum) or legumes (beans, groundnuts) — these do not host the wilt, so they clean the land while you rest it.

Choose warm, open ground that drains freely — a gentle slope or a sandy loam. Avoid low, wet hollows and heavy clay where water sits; soggy roots rot, and the wilt strikes harder there.

Keep well away from any old melon-family patch nearby, and never carry soil or tools across from a field where vines wilted and died last year — that is how the wilt travels.

Buy certified seed in a sealed, labelled bag from a known dealer — not loose seed scooped from a sack. Check this season's packing date on the label.

Pick a variety that suits your market and your season: watermelon needs about 80–110 warm days from sowing to harvest. Ask the dealer or check your recommendation.

Seedless (triploid) types only: 'triploid' just means the plant makes no good pollen of its own. So also buy a seeded variety as a pollenizer and plan to plant one pollenizer for every 2–3 seedless plants — without it the bees have no pollen to carry and no fruit sets.

Buy the basal fertiliser your recommendation gives — watermelon wants steady phosphorus and potassium far more than heaps of nitrogen. Buy any boron or calcium your recommendation calls for at the same time (they help the fruit set and fill).

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

Mark out a wide grid: rows about two-and-a-half strides apart (2.4 m) and stations about a stride and a half apart (1.4 m) along the row. The vines sprawl far — give them the room; you cannot squeeze in more plants without losing fruit.

At each station, loosen the soil deep (watermelon roots go down over a metre) and pull it up into a low, flat-topped mound about two hand-spans across (½ m), raised a little above where rainwater would stand.

Work a few handfuls of well-rotted manure (dark, crumbly, no strong smell) and the basal fertiliser your recommendation gives into each mound — mixed into the soil, not left sitting on top.

Build the mounds in the weeks before sowing so they settle and warm through, and where they catch sun all day.

Only sow once the soil is truly warm — over about 18 °C. Feel it at dawn: it should be warm, not cold, to your hand. Watermelon seed rots in cold soil, so wait for settled warm weather even if it means sowing a week later.

On each prepared mound, drop 2–3 seeds spread a little apart (not in one clump), 1.3–2.5 cm deep — no deeper than the top joint of your finger (fingertip to the first knuckle, about 2 cm). Go a little deeper in dry sand, shallower in heavier soil. Point each seed's narrow, pointed end downward if you can.

The basal should already be worked into the mound. If you add a little at sowing, keep it a hand-span (20 cm) out from the seed and never touching it, or it burns the sprout.

Cover and firm the soil gently so each seed sits snug in warm, moist earth.

Seedless types: sow your pollenizer seed to the same plan — one pollenizer for every 2–3 seedless stations — and mark the pollenizer plants (a stick or a ribbon) so you know them at flowering.

Once the seedlings are up with their first true leaves, keep the strongest one or two per station and pinch the rest off at ground level so the keepers aren't crowded.

From about 5 days after sowing, walk all the mounds every 3–4 days — don't just check the row by the path.

Cucumber beetles: look for small yellow-and-black or reddish beetles feeding on the leaves and stems, and the ragged holes they chew. They also spread a wilt, so knock their numbers down early by hand-picking into a tin of soapy water.

Aphids: look under the leaves for clusters of tiny soft green or black insects, sticky shiny leaves, and ants running up the plants — aphids carry viruses.

Damping-off: look for seedlings that suddenly flop over with a thin, dark, pinched, water-soaked stem at the soil line. It spreads in cold, wet, crowded mounds — so don't over-water, and thin any crowded stations.

Note any gaps (stations where nothing came up) so you can decide whether to re-sow while the soil is still warm.

Do not spray insecticide if the crop is anywhere near flowering later — hand-pick pests instead; the bees you will soon need are worth far more than the beetles you'd kill.

About a week after sowing, walk the mounds and count how many stations have at least one healthy seedling against the number you sowed.

Work out the share that came up — for example, 8 stations with plants out of every 10 sown = 80%.

80% or more (8 in 10) → a good stand, carry on.

Fewer than 80% → re-sow the empty stations now, while the soil is still warm, so the fill-ins can catch up.

If it fails — the gaps are widespread, or a re-sow still doesn't come up — re-sow the whole patch rather than nurse a half-empty field all season.

Keep the mound moist but never waterlogged — damp like a wrung-out cloth, not muddy.

Water every 3–5 days, more often in heat and on sandy mounds that dry fast. Check by pushing a finger in — water when the top few centimetres are dry.

Water at the base in the cool of the morning, and try to keep the leaves dry to slow off disease.

Weed by about 2–4 weeks after sowing, before the vines start to run and while you can still step between the mounds.

Hoe shallowly around the plants — watermelon has wide, near-surface feeder roots, so deep hoeing near the stem cuts them.

Pull weeds close to the stem by hand, roots and all — chopping only the tops lets them spring back.

Leave the pulled weeds or some straw as a mulch between the mounds — it holds moisture, smothers the next flush, and later gives the fruit a clean, dry bed to lie on.

About 2–3 weeks after sowing, as the vines start to run, side-dress the nitrogen amount your recommendation gives — no more.

Band it in a line about a hand-span (20 cm) out from the stem along the row — never against the stem or on the leaves.

Apply onto moist soil (after watering or light rain) and cover or water it in, so it feeds the plant instead of gassing off into the air.

Save the plant's big potassium feed for fruit-sizing later — potassium is what makes fruit and sweetness, not nitrogen.

Every 3–4 days, walk the crop and turn over leaves at several plants across the field.

Aphids / whitefly: look under the leaves for clusters of tiny green or black aphids, or tiny white flies that puff up in a little cloud when you brush the vine — both leave leaves sticky and shiny and spread virus.

Cucurbit virus: look for leaves mottled light-and-dark green (a 'mosaic' pattern), crinkled or puckered, and vines that stay stunted. There is no cure — pull and destroy badly affected plants so they don't seed the rest.

Powdery mildew: look for white powdery patches, like a dusting of flour, on the leaves. Downy mildew: look for angular yellow blotches on the top of the leaf (boxed in by the veins) with grey-purple fuzz underneath in wet weather.

Fusarium wilt: look for a runner or whole plant that wilts in the heat of the day and does NOT recover overnight, then yellows and dies; a split stem shows brown streaks inside. Pull affected plants — and remember this land now owes its long rotation break.

Note what you see and where. If a disease is spreading, act — open the matching guide.

Water every 5–7 days, enough to wet the soil deep where the long roots are — water well but less often, rather than a daily sprinkle.

Keep it even — don't let the vines wilt and then flood them; steady moisture avoids stress.

Water at the base in the morning and keep the leaves as dry as you can to slow mildew.

Do not spray any insecticide while the crop is flowering — not even for beetles or aphids. If a pest is truly serious, hand-pick it, or wait until the day's flowers have closed.

Give bees a reason to visit: leave some flowering weeds or hedge plants near the field, and don't clear every flowering plant from the edges.

If you keep bees or know a beekeeper, hives set near the field during bloom greatly lift fruit set.

Watch each morning: busy bee traffic on the yellow flowers means fruit is setting. Few or no bees → plan to hand-pollinate (next task).

Go out in mid-morning (about 9–11 am), when the flowers are freshly open and the pollen is ready.

Tell the flowers apart: a male flower sits on a plain thin stalk; a female flower has a tiny marble-sized melon just behind its petals. You move pollen from male to female.

Pick a fresh open male flower, peel its petals back to bare the yellow centre, and dab that yellow pollen onto the centre of each open female flower. One male can serve several females; take a fresh male when the pollen runs low.

For seedless crops, take the pollen from your pollenizer (seeded) plants — that is the whole reason they are in the field.

Do this every morning through flowering while bees are few — each female flower is open one morning only, so a missed morning is a missed melon.

Keep the soil evenly moist right through flowering and fruit-set — water every 3–5 days, more often in heat. Never let the vines wilt now, even for a day.

Water evenly. A big drink after a dry spell causes blossom-end rot — a sunken, brown-black leathery patch on the flower end of the young fruit — because calcium can't reach the fruit when the watering swings.

If your recommendation includes calcium or boron, this is the stage they help the fruit set well and fill evenly — apply as directed.

Water at the base and keep the leaves dry to hold off mildew.

Every 3–4 days, check the young fruit and the leaves.

Melon fly: look for tiny needle-prick scars that weep a drop of sap on young fruit, soft sunken patches, and fruit that rots or drops early. Cut a spoiled one open and you'll find white maggots inside.

Pick up and destroy (bury deep or burn) every stung or rotten fruit — don't leave them lying, or the maggots crawl into the soil and the next generation is worse.

Mildews: keep checking leaves for the white flour-like patches (powdery) or angular yellow blotches with fuzzy undersides (downy), especially in damp weather.

If melon fly is active, hang simple bait traps and consider covering the youngest fruit. Time any spray for the evening — and if you do spray, cover your skin, nose and eyes, keep the wind at your back and away from food, respect the pre-harvest interval (the set number of days you must wait between spraying and picking so the poison clears the fruit), and wash well afterwards.

Once fruit are about fist-sized, slip a pad of dry straw, grass or leaves (or a tile or board) under each melon to lift it off the damp soil.

Gently turn each fruit a little every week or two so all sides get sun and colour evenly and no side sits wet — but turn carefully, without twisting or kinking the stalk.

Keep the bedding dry; replace it if it rots down.

As the fruit begins to size (about 7–10 weeks after sowing), side-dress the potassium amount your recommendation gives.

Band it about a hand-span (20 cm) out from the stem on moist soil, and water it in so it reaches the roots.

Keep moisture even through sizing — steady water plus potassium gives big, sweet, firm fruit; feast-and-famine watering gives splits and dull flesh.

This is the fruit-and-sugar feed: unlike nitrogen, potassium builds fruit, not leaf, so don't skip it.

From about a week before harvest (roughly day 80 onward, as the fruit reach full size and start to ripen), cut watering right back — give only enough to keep the vines from collapsing.

Never follow a dry spell with a big soaking now — that sudden drink is exactly what splits ripe fruit. If you must water, water only a little.

Let the fruit finish on the drier side — this is what pulls the flesh sweet instead of bland and watery.

Start checking from about 35 days after the fruit set (roughly day 80 from sowing). Judge ripeness by three signs together, never just one:

Tendril: the little curly 'pig-tail' tendril on the vine nearest the fruit has dried and turned brown.

Ground spot: the patch where the melon sits on the ground has turned from white to a creamy, buttery yellow (a white ground spot means it's not ready).

Skin and sound: the skin has gone dull, not shiny, and the melon gives a deep, hollow thump (like knocking on your chest) when you tap it — a high, tight ring means unripe.

When the signs agree, cut the stalk with a knife (don't pull or twist), leaving a short stub of stalk on the fruit. Handle it gently — watermelons bruise and crack if dropped or thrown.

Make a main pick, then pass again every 5–7 days for the fruit that ripen later — about 2–3 melons per plant over roughly two weeks.

If the signs don't agree — green tendril, white ground spot, or a tight ringing sound — leave the melon and check again in a few days. It will not sweeten after picking, so never pick on hope.