Pelham Gardens
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Watermelon

The most ambitious cucurbit to grow in a UK garden. Watermelon needs more heat and a longer season than melon or cucumber, so success depends on a warm greenhouse, a compact variety, and a good summer — but there are few more satisfying harvests when it comes off.

Waiting this month
Great for kids
First sprouts in 7–14 days, needs 22–25°C to germinate reliably

Difficulty

Watermelon

Out of season right now. The next sowing window opens in April.

Growing Calendar

Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Sow
Transplant
Harvest

This month: Jul

Plan ahead for this crop

  • Check growing conditions
  • Prepare for next stage

Sowing Guide

What you'd find on the seed packet

Sow Depth

1cm

Spacing

60–90cm

Germination

7–14days, needs 22–25°C to germinate reliably

Thinning

Sow one seed per pot — no thinning needed

Grower's Note

Use a heated propagator — watermelon seed is slow and unreliable to germinate below 20°C. Choose a compact variety bred for shorter, cooler seasons.

Planting Out Guide

Best spaces, conditions and how to plant out

Plant Spacing

60–90cm, or one plant per large growbag

Best Grown In

Greenhouse borders or large containers under cover; only the warmest, most sheltered outdoor gardens in a good year

Conditions

Full sun, as much warmth as possible. Rich, free-draining compost. Do not plant out until night temperatures are reliably above 14°C.

Grower's Note

Mulch with black polythene or membrane to warm the soil and suppress weeds. Support developing fruit off the ground on a tile or piece of wood to prevent rot.

Growing Stages

Approximate weeks from sowing to harvest

Sprouting

1wks

Seeds germinate and first leaves emerge. Keep warm and moist.

Establishing

6wks

Root system develops and plant builds structure. Pot on if needed.

Maturing

13wks

Plant reaches full size and begins producing. Harvest at peak.

Total~20 weeksfrom seed to harvest

Companion Plants

Plant these nearby for natural pest control, better yields, and healthier soil.

Climate Control

Today

C

Humidity

%

Water

Daily

Sunlight

6+ hours direct sun

Watch Out For

The UK growing season is genuinely marginal for watermelon

even with care, some years won't produce ripe fruit; treat it as an ambitious, fun project rather than a reliable crop

Powdery mildew and red spider mite build up fast in the hot, dry conditions the plant needs

check leaves regularly and improve airflow

Fruits need consistent warmth to ripen

a poor late summer can leave watermelons large but bland and underripe

What You'll Need

Equipment for growing watermelon

Modular Seed Tray

96-cell for precision sowing

Fine Rose Watering Can

Gentle shower for seedlings

Bamboo Canes

Pack of 20 × 120cm

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Grown Organically

Every method in this guide works with natural systems — no synthetic chemicals, no shortcuts.

Read our approach

Common Questions

About growing Watermelon in the UK

Can watermelon really be grown in the UK?

Yes, but it's genuinely the most challenging common fruit to ripen in a UK climate. Success is far more likely in a greenhouse or polytunnel, with a compact early variety like 'Sugar Baby', and in a warm summer. Treat it as an ambitious project rather than a guaranteed harvest.

How do I know when a watermelon is ripe?

Look at the curly tendril nearest the fruit's stem — it turns brown and dry when the melon is ripe. The underside resting on the ground should turn from white to a pale yellow (the 'ground spot'), and a ripe fruit sounds hollow when tapped.

Why is my watermelon plant not producing fruit?

Usually poor pollination in cool, wet weather, or too much nitrogen feeding producing lush leaves at the expense of flowers. Hand-pollinate female flowers (small round swelling behind the petals) with a male flower each morning, and switch to a high-potassium feed once flowering starts.

How many watermelons will one plant produce?

In a UK garden, 2–3 fruits per plant is a realistic, good outcome — large American varieties may only manage one. Compact varieties bred for shorter seasons are far more likely to ripen multiple fruit before autumn.

Member guides

There's more to growing Watermelon than this guide covers.

Seasonal reminders, deeper guides, and the small adjustments that change a harvest.

See what's included

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Each month: what to sow now, what to move on, and organic growing tips matched to UK conditions.

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