How to Grow Watermelon
Citrullus lanatus
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.
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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.
Companion Planting
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Growing Conditions
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- Sow indoors
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- Transplant out
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- 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.
Care Guide
- Feeding
- High-potash liquid feed weekly once fruits start swelling. Reduce watering as fruits approach maturity to concentrate sweetness.
- Watch for
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- Fusarium wilt
- Powdery mildew
- Aphids
- Cucumber beetles
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.
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