How to grow Watermelon

Citrullus lanatus

Large, sweet, juicy fruit grown as a warm-season annual. Requires a long, hot growing season and plenty of space for vines to spread.

Watermelon — Photo: Fred Hsu ( Wikipedia:User:Fred Hsu on en.wikipedia ), CC BY-SA 3.0, Wikimedia Commons

Quick facts

Type	Vegetable
Family	Cucurbitaceae
Light	Full sun
Soil pH	6–6.8
Frost	does not tolerate frost
Soil for sowing	from 18 °C
Germination	7 days
Seedlings ready	25 days
Sowing to harvest	90 days
Where it grows	Greenhouse, Open ground, At home

When to plant

Sow for seedlings about 5 weeks before planting out.

Plant out in open ground about a week after your last spring frost, once the soil is warm.

In an unheated greenhouse everything moves about three weeks earlier.

The first harvest comes about 90 days after the shoots appear.

Care

Greenhouse

Stage	Watering	Temperature	Feeding
Seedlings	every 2 days	20…28 °C	balanced (NPK), 10 days into the stage
Growth	every 4 days	22…30 °C	balanced (NPK), 14 days into the stage
Flowering	every 5 days	24…32 °C	phosphorus and potassium, at the start of the stage
Fruiting	every 4 days	24…32 °C	potassium, at the start of the stage; potassium, 21 days into the stage

Open ground

Stage	Watering	Temperature	Feeding
Seedlings	every 2 days	20…28 °C	balanced (NPK), 10 days into the stage
Growth	every 5 days	20…30 °C	balanced (NPK), 14 days into the stage
Flowering	every 6 days	22…32 °C	phosphorus and potassium, at the start of the stage
Fruiting	every 5 days	22…32 °C	potassium, at the start of the stage; potassium, 21 days into the stage

At home

Stage	Watering	Temperature	Feeding
Seedlings	every 2 days	20…25 °C	balanced (NPK), 10 days into the stage
Growth	every 3 days	20…26 °C	balanced (NPK), 14 days into the stage

Growing notes

Light

Needs full sun — at least 8 hours daily; poor fruit development occurs in shade.

Soil

Deep, well-drained, sandy loam enriched with compost; avoid waterlogged soils.

Care

Start seeds indoors 2–3 weeks before the last frost or sow directly when soil is warm. Keep soil consistently moist during early growth, but reduce watering as fruits ripen to improve sweetness. Hand-pollinate flowers in greenhouses if bees are absent.

How to tell it is ripe

The ground spot where it lies on the soil has turned from white or pale green to creamy yellow.
The curly tendril nearest the fruit has turned brown and dry.
The rind has lost its gloss and looks dull.
The rind resists your thumbnail and feels rough.
Thump it: a high metallic ping means unripe and a dull thud can mean overripe, so trust sound only together with the other signs.
Pick only when several signs agree, because a watermelon does not ripen any further once it is off the vine.

Pests and diseases of Watermelon

Anthracnose
Bacterial wilt
Cucumber beetles
Downy Mildew
Fruit cracking
Fusarium Wilt
Leaf Curl Virus
Two-spotted spider mite
Verticillium Wilt
White mould (Sclerotinia)
Whitefly

Sources

Figures cited from these sources.