How to grow watermelon
Overview
Watermelon (Citrullus lanatus) is a fast-growing warm-season vine prized for its large, sweet fruit. It requires full sun, steady warmth, and consistent moisture during fruit development. Space generously and wait until soil is warm before planting.
Varieties
- Sugar Baby — Compact, early-maturing (80 days) with 4–6 kg fruits; ideal for small gardens and cooler areas.
- Crimson Sweet — Large, striped fruits (8–12 kg) with very sweet flesh; popular in Australian home gardens.
- Jubilee — Oblong, heat-tolerant variety (90–100 days) with striped rind and excellent flavour; suited to tropical climates.
- Mini Love — Personal-sized (1–3 kg) seedless watermelon; matures in 70–80 days and grows well in pots.
Soil Preparation
Prefers sandy loam with a pH between 6.0 and 7.0. Enrich soil with well-rotted manure or compost before planting, and ensure excellent drainage to prevent root rot. Raised beds or mounds improve drainage in heavy soils.
Growing Guide
Plant in well-drained sandy loam enriched with compost. Sow 2–3 seeds per mound 2–3 cm deep, spacing mounds 1.5–2 m apart. Thin to the strongest seedling. Use black plastic mulch to warm soil and conserve moisture, and install drip irrigation to avoid wetting foliage. Trellising is possible for small-fruited varieties but not necessary.
Sowing
Direct sow seeds 2–3 cm deep, 3 per mound spaced 1.5–2 m apart. Germination takes 7–14 days when soil temperature is above 20°C. Watermelon can be transplanted if care is taken to minimise root disturbance, but direct sowing is preferred.
Care
Feed every 2–3 weeks with a potassium-rich liquid fertiliser once vines begin to run. Prune to 2–3 main vines per plant to concentrate energy on fewer, larger fruit. Remove any fruit that sets after late summer in temperate zones to allow remaining melons to ripen fully.
Companion Planting
Watermelon grows well with corn and radish, which share similar growing conditions. Beans and nasturtiums are also beneficial companions that fix nitrogen or repel pests. Avoid planting near other cucurbits to reduce the risk of disease spread.
Common Pests & Risks
Aphids and mites can attack watermelon leaves, causing stunting and reduced yields. Powdery mildew appears as white coating on leaves in humid conditions. Control aphids with a strong water spray or insecticidal soap, and manage mildew with sulfur sprays and improved airflow. Cucumber beetles may also transmit bacterial wilt.
Harvesting
Harvest when the underside of the fruit turns from white to deep yellow and the small tendril nearest the fruit stem dries and browns. A thump test producing a dull, deep sound also indicates ripeness. Cut the stem rather than pulling to avoid damaging the vine.
In the Kitchen
Eat fresh, in fruit salads, or blend into juices and smoothies. Store whole watermelon at room temperature for up to a week; refrigerate cut pieces for 3–4 days in sealed containers. Grilled watermelon slices with salt and lime add a savoury twist.
Troubleshooting
Weak or leggy vines: insufficient sunlight or overcrowding – thin plants and ensure full sun. Blossom end rot: calcium deficiency from uneven watering – maintain moist soil. Powdery mildew: white coating on leaves – improve air circulation and apply sulfur spray. Fruit not sweet: inadequate heat or overwatering during ripening – reduce water as fruit matures. Splitting fruit: irregular watering after fruit set – water consistently, especially in dry spells.