How to Grow Watermelon
Citrullus lanatus
Watermelons need a long, hot growing season with maximum sun — in cool climates a greenhouse or polytunnel is essential. Start seeds indoors 3–4 weeks before the last frost and transplant into warm, fertile soil. Once 2–3 fruits have set, pinch out growing tips to concentrate energy into ripening. Reduce watering as fruits reach full size; a hollow sound when tapped indicates they are ripe.
When to Start
Start seeds indoors 4 weeks before your last frost date. Transplant outdoors once night temperatures stay above 12°C and soil has warmed to at least 18°C.
Don't know your frost date? Find it here →
Growth Stages
Approximate days from start
Care Essentials
- High-potash liquid feed weekly once fruits start swelling. Reduce watering as fruits approach maturity to concentrate sweetness.
- Watermelons need a long warm season and maximum sun — in cool climates a greenhouse or polytunnel is essential. Reduce watering significantly once fruits are full-size to concentrate sweetness; a hollow thud when tapped indicates ripeness.
Growing Conditions
- Min. soil temperature
- 18°C+
- Germination temperature
- 21–30°C
- Sow indoors
- —
- Transplant out
- —
- First harvest
- —
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Spacing & Planting
| Plant spacing | 120 cm |
| Row spacing | 180 cm |
| Sow depth | 2.5 cm |
| Mature height | 40 cm |
| Mature spread | 200 cm |
Watermelons are vigorous, sprawling vines that need a lot of room. Compact or 'icebox' varieties can be grown in smaller spaces at 90 cm apart.
Pests & Diseases
Pest Aphids
Identification: Clusters of small soft-bodied insects on shoot tips and leaf undersides, sticky honeydew, curled or distorted new growth.
- Strong water spray to dislodge colonies
- Introduce ladybirds or lacewing larvae
- Neem oil spray
- Insecticidal soap
- Approved systemic aphicide
Pest Cucumber Beetles
Identification: Small yellow-green beetles with black spots or stripes feeding on leaves, flowers and fruit rind. Larvae attack roots.
- Row covers until flowering
- Hand-pick adults
- Kaolin clay spray
- Pyrethrin-based insecticide
- Approved contact insecticide
Pest Spider Mites
Identification: Fine webbing on leaf undersides, stippled yellow leaves, thrives in hot dry conditions.
- Increase humidity by misting
- Biological control (Phytoseiulus persimilis)
- Neem oil spray
- Approved miticide for cucurbits
Disease Fusarium Wilt Fusarium oxysporum f. sp. niveum
Symptoms: Wilting of individual vines starting from the base, yellowing leaves, brown discolouration inside stems when cut.
Treatment: Remove and destroy affected plants. No chemical cure once established. Solarise soil before replanting.
Prevention: Use resistant varieties, practise 5-year crop rotation, avoid overwatering, use grafted rootstock.
Disease Anthracnose Colletotrichum orbiculare
Symptoms: Dark sunken circular spots on leaves, stems and fruit. Spots may produce salmon-pink spore masses in wet weather.
Treatment: Remove infected plant material. Apply approved copper-based fungicide preventively.
Prevention: Use resistant varieties, ensure good air circulation, avoid overhead watering, practise crop rotation.
Disease Powdery Mildew Podosphaera xanthii
Symptoms: White powdery coating on upper leaf surfaces, leaves yellow and dry out, reduced fruit quality.
Treatment: Remove badly affected leaves. Apply sulphur-based or potassium bicarbonate fungicide.
Prevention: Choose resistant varieties, ensure good spacing and air circulation, avoid overhead watering.
Growing Conditions
| Min. soil temperature | 18°C |
| Germination temperature | 21–30°C |
| Base growth temperature | 12°C |
| Min. daylength to start | 11h |
| Photoperiod sensitivity | day neutral |
Frequently Asked Questions
- How far apart should I plant Watermelon?
- Plant Watermelon 120cm apart with 180cm between rows.
- When can I harvest Watermelon?
- Watermelon is ready to harvest approximately 80 days after transplanting.
- Is Watermelon frost hardy?
- Watermelon is classified as Tender.
