What Fertiliser Is Best for Watermelon?

The best fertiliser for watermelon is a balanced NPK blend that supports vigorous vines, strong flowers, and sweet fruit. In Australia, the most reliable option is
CompleteGrow NPK 20-20-20. This water-soluble fertiliser delivers equal parts nitrogen, phosphorus, and potassium, ensuring steady leaf growth, root strength, and fruit sweetness without risking nutrient imbalances.

Why Balanced Fertiliser Works Best

Nitrogen (20%): Encourages strong leaf and vine development, essential early in the season.
Phosphorus (20%): Strengthens roots and supports flowering, helping female flowers set fruit.
Potassium (20%): Improves fruit size, sweetness, and disease resistance during ripening.

Unlike high-nitrogen fertilisers, which can cause leafy growth without fruit, NPK 20-20-20 ensures watermelons develop evenly from seedling to harvest.

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How to Fertilise Watermelon Plants

Seedling stage: Apply half-strength fertiliser once true leaves appear. This encourages root establishment without burning young plants.
Vine growth: Use full-strength applications (4 mL/L) every 7–10 days to fuel rapid leaf and runner development.
Flowering & fruit set: Continue regular feeding to maintain strong vines and improve pollination success.
Fruit development: Maintain balanced fertilising every 10–14 days. Potassium supports sugar build-up and fruit size at this stage.

Best Application Methods

Soil drench: Dissolve fertiliser in water and apply at the base of vines.
Foliar spray: Use a diluted solution on leaves early morning for quick nutrient uptake.
Always water first: Moist soil prevents root burn and ensures nutrients absorb evenly.

Following this schedule with
CompleteGrow NPK 20-20-20 ensures strong vines, plenty of flowers, and sweet, full-sized melons.

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FAQs: Fertiliser for Watermelons

Can I use general garden fertiliser on watermelons? Only if it’s balanced and low in urea. High-nitrogen blends often cause excessive vine growth with poor fruit set. Balanced NPK 20-20-20 is safer and more effective.

How often should I fertilise watermelon plants? Every 7–10 days during active growth, and every 10–14 days once fruits begin sizing up. Consistency is key.

Do potted watermelons need more fertiliser? Yes. Nutrients wash out faster in pots, so feed half-strength weekly and flush pots monthly to prevent salt build-up.

What happens if I over-fertilise? Too much fertiliser can burn roots and delay fruiting. Always follow recommended rates — more is not better for watermelons.

With steady feeding, healthy soil, and proper watering, watermelons reward you with vigorous vines and delicious summer fruit.