How to Feed Watermelons: Organic Options (2025)

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Prepare Rich Soil Before Planting Early Feeding Schedule: Seedling to First Flower Feeding During Flowering and Fruit Development Organic Options That Work Well Summary: Feeding Watermelons for Sweet Success Written by Stephen Albert

byStephen Albert

Watermelons are among the hungriest plants in the vegetable garden. After decades of growing them in hot-summer gardens, I’ve learned that feeding them properly—starting at soil prep and continuing through fruit development—makes the difference between a so-so harvest and bushels of crisp, flavorful melons.

Whether you grow organically or use conventional fertilizers, this guide will help you understand what nutrients watermelons need, when to apply them, and how to choose the best feeding method.

Table of Contents

Prepare Rich Soil Before Planting

Healthy watermelon growth starts with the soil. I always amend the planting beds well before the first seed or transplant goes in the ground:

In fall or early spring, spread several inches of aged compost or well-rotted manure across your watermelon bed.
Turn the soil to at least 12 inches (30 cm) deep to allow for root expansion and to evenly distribute nutrients.
If you prefer a ready-made solution, use a commercial organic planting mix designed for heavy feeders.

This foundational feeding sets up the vines for vigorous early growth.

Early Feeding Schedule: Seedling to First Flower

From transplanting or germination until the first female flowers appear, watermelon vines benefit from a gentle but steady diet:

Use a diluted fish emulsion fertilizer (1 tablespoon per gallon of water).
Apply weekly as a soil drench or foliar spray.
Organic growers can alternate with compost tea or manure tea every 2 to 3 weeks.

💡 Experience Tip: Mark your calendar when the first female flowers open. Watermelons typically ripen 35 days after pollination, and your feeding routine should shift accordingly.

Feeding During Flowering and Fruit Development

Once flowering begins and fruits start to form, watermelon vines shift from leafy growth to fruit production. This is when you’ll want to change up your fertilizer mix:

Reduce nitrogen to avoid excessive vine growth at the expense of fruit.
Increase phosphorus and potassium to support fruit development and sweetness.

Fertilizer options:

Organic side dressing: Apply compost or aged manure every 2 to 3 weeks around the root zone.
Liquid feeding: Continue fish emulsion or switch to compost tea, but only every few weeks.
Granular organic fertilizers: Use a balanced blend early (e.g., 10-10-10), then switch to a 5-10-10 or low-nitrogen blend once fruits appear.

How to side-dress:
Sprinkle fertilizer a few inches from the base of the vines (not on them), then water deeply to help nutrients reach the roots.

Organic Options That Work Well

Over the years, I’ve found that watermelons respond best to natural, slow-release feeds. Here are some favorites:

Aged manure – Excellent for early soil building and slow nutrient release.
Fish emulsion – Ideal for leafy growth and early plant health.
Compost tea – Gentle feeding that builds soil microbes.
Bone meal – High in phosphorus, perfect for flowering and fruit set.
Wood ash or greensand – Boosts potassium, enhances fruit flavor and firmness.

Make sure your soil is warm and moist before applying organic fertilizers—especially those high in phosphorus or potassium—as nutrients are absorbed better under these conditions.

Summary: Feeding Watermelons for Sweet Success

Growth Stage	Fertilizer Type	Frequency
Pre-planting	Aged compost or manure	Fall or early spring
Seedling to first flower	Fish emulsion (1 Tbsp/gallon)	Weekly
After flowering	5-10-10 or compost tea	Every 2–3 weeks
During ripening	Reduce or stop feeding	Final 2 weeks

Feeding watermelons isn’t complicated, but timing and balance are critical. Too much nitrogen late in the season will give you massive vines and bland fruit. Not enough nutrition early on, and your vines may stall before the fruit can grow.

When you prepare the soil deeply, feed consistently, and shift to fruit-supporting nutrients at the right time, you’ll grow sweet, juicy melons that are packed with flavor—and you’ll do it with confidence and care.

Written by Stephen Albert

Stephen Albert is a horticulturist, master gardener, and certified nurseryman who has taught at the University of California for more than 25 years. He holds graduate degrees from the University of California and the University of Iowa. His books include Vegetable Garden Grower’s Guide, Vegetable Garden Almanac & Planner, Tomato Grower’s Answer Book, and Kitchen Garden Grower’s Guide. His Vegetable Garden Grower’s Masterclass is available online. Harvesttotable.com has more than 10 million visitors each year.