How to Fertilize Watermelon Plants in Australia

To fertilise watermelon plants, apply a balanced liquid feed every 7–10 days during active growth, switching to slightly lower nitrogen once fruit sets. In Australia, the most reliable option is
CompleteGrow NPK 20-20-20, which supports healthy vines, strong flowering, and large, sweet fruit without the risk of nutrient imbalance.

Why Fertiliser is Crucial for Watermelons

Heavy feeders: Watermelons sprawl, grow quickly, and demand constant nutrition through roots and foliage.
Shallow roots: Nutrients leach quickly in sandy soils, especially in summer heat.
Balanced nutrition: Excess nitrogen causes leafy vines with few flowers, while low potassium reduces fruit size and sweetness.

Consistent feeding from seedling to harvest ensures vines stay vigorous, flowers set properly, and fruit develops to full size and flavour.

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Feeding Schedule for Watermelon Plants

Seedling stage (0–4 weeks): Apply half-strength NPK 20-20-20 every 7 days to encourage root and leaf growth.
Vegetative stage (4–6 weeks): Switch to full-strength applications (4 mL/L water) every 7–10 days to support vines and early flowers.
Flowering to fruit set: Maintain balanced feeding weekly. Ensure deep watering after each application to prevent salt build-up.
Fruit sizing & ripening: Continue feeding every 10–14 days. Keep nitrogen moderate and potassium strong to enhance fruit weight and sweetness.

Best Way to Apply Fertiliser

Liquid feed: Dissolve NPK fertiliser in water and apply directly to the soil around vines.
Foliar spray (optional): Apply diluted feed to leaves early morning for quick correction of deficiencies.
Water first, fertilise second: Always water soil before feeding, then lightly water again to wash nutrients to the root zone.

Regular feeding with
CompleteGrow NPK 20-20-20 ensures vigorous vines and sweet, full-sized melons across Australian climates.

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Common Fertilising Problems & How to Avoid Them

Excess nitrogen: Vines grow rapidly but fruiting is delayed. Solution: stick to balanced fertilisers like NPK 20-20-20.
Pale leaves or weak growth: Underfeeding or nutrient leaching. Increase feeding frequency and mulch beds.
Blossom-end rot: Irregular watering and calcium imbalance. Maintain even moisture and ensure a balanced nutrient supply.

FAQs: Fertilising Watermelon Plants

What is the best fertiliser for watermelon plants? The best option is a balanced fertiliser such as CompleteGrow NPK 20-20-20, which provides equal parts nitrogen, phosphorus, and potassium for steady growth and fruit development.

How often should I fertilise watermelon plants? Apply every 7–10 days during active growth and every 10–14 days once fruits are developing.

Can I fertilise potted watermelons? Yes. Use half-strength NPK 20-20-20 every 7 days, and flush pots with clean water monthly to prevent salt build-up.

Do watermelons need different fertiliser at fruiting? No special product is required—just maintain a balanced formula and avoid overloading nitrogen during ripening.

Feed consistently and water deeply, and your watermelon vines will reward you with large, sweet fruit all summer.