When To Plant Watermelon In Southern California

If you’re planning to grow watermelon in Southern California, timing is your first and most important step. Knowing exactly when to plant watermelon in Southern California sets the stage for a succesful harvest of sweet, juicy fruit.

Our long growing season is a huge advantage, but the specific timing can vary a bit from the coast to the inland valleys and deserts. Planting at the right moment ensures your vines get the warm soil and consistent heat they need to thrive. Let’s break down the optimal schedule so you can plan your garden calendar perfectly.

For most of Southern California, the prime planting window is from late March through May. The golden rule is to wait until both the soil and the air are reliably warm. Watermelons are tropical plants and they will not tolerate cold, damp conditions.

Here’s a more detailed regional guide:

Coastal Areas (San Diego, Los Angeles, Orange County): Aim for April to early June. Coastal fog and cooler nights mean you should wait a little longer for the soil to warm up thoroughly.
Inland Valleys & Warm Microclimates (Riverside, San Bernardino): This is ideal watermelon country. You can often start as early as late March and continue planting through May.
Desert Regions (Palm Springs, Imperial Valley): The season is shifted. Here, you have two options: plant in late February to early April for a summer harvest, or plant in late August to September for a fall harvest, avoiding the most intense summer heat.

A simple soil test is the best indicator. Push your finger into the soil. If it feels warm to the touch, not cool, it’s probably time. For precision, use a soil thermometer—you’re looking for a consistent temperature of 70°F (21°C) or higher.

Choosing the Right Watermelon Variety

Selecting a variety suited to our climate and your garden size is crucial. Some types need more space or a longer season than others.

Icebox Types (Smaller): Perfect for smaller gardens. ‘Sugar Baby’ and ‘Golden Midget’ mature in about 75-80 days.
Picnic Types (Larger): Need more room. ‘Crimson Sweet’ and ‘Charleston Gray’ are classic, reliable choices maturing in 85-95 days.
Seedless Varieties: Popular but require a bit more care. You must plant a seeded “pollinator” variety nearby. ‘Triple Sweet’ is a good option. They often take 80-90 days.

Always check the “days to maturity” on the seed packet or plant tag and count backward from your area’s first fall frost date (usually late November or even December in SoCal) to ensure you have enough time.

Step-by-Step Planting Guide

Follow these steps to get your watermelon seeds or transplants off to a strong start.

1. Site Selection and Soil Preparation

Watermelons demand full sun—at least 8 hours of direct light daily. They also need exellent drainage. Prepare the soil 2-3 weeks before planting.

Choose the sunniest spot in your yard.
Work in a generous 3-4 inch layer of compost or well-rotted manure to a depth of about 12 inches.
Consider forming raised mounds or hills about 8 inches high and 3 feet wide. This improves drainage and warms the soil faster.

2. Planting Seeds Directly vs. Using Transplants

You can suceed with either method in our climate.

Direct Sowing (Recommended):

Plant seeds 1 inch deep in your prepared hills.
Place 4-6 seeds per hill, spacing them a few inches apart.
Once seedlings have 2-3 true leaves, thin to the 2-3 strongest plants per hill.

Using Transplants:

Start seeds indoors about 2-3 weeks before your outdoor planting date. Use biodegradable pots to avoid disturbing roots.
Harden off seedlings for a week before transplanting.
Plant them carefully, keeping the soil level the same as in the pot.

3. Spacing for Success

This is where many gardeners go wrong. Watermelon vines need ample space.

Space hills 4-6 feet apart for smaller varieties.
Allow 6-8 feet between hills for larger, vining types.
If planting in rows, space rows 6-10 feet apart.

Essential Care Through the Season

Consistent care is key to developing those sweet, juicy melons.

Watering Deeply and Wisely

Watermelons have deep roots. Water deeply and infrequently to encourage strong root growth. Provide 1-2 inches of water per week.

Use drip irrigation or soaker hoses to keep foliage dry and prevent disease.
Reduce watering significantly during the last week or two before harvest. This concentrates the sugars for sweeter fruit.

Feeding Your Plants

They are moderate feeders. At planting, mix a balanced organic fertilizer into the soil. When vines begin to “run” (spread), side-dress with a fertilizer lower in nitrogen and higher in phosphorus and potassium to promote flowering and fruiting.

Weeding and Mulching

Keep the area around young plants weed-free. Once vines spread, apply a 3-4 inch layer of straw or other organic mulch. This conserves moisture, suppresses weeds, and keeps the developing fruit clean and off the damp soil.

Harvesting Your Southern California Watermelons

Harvest time is the best reward! Most varieties mature 80-100 days after planting. Here’s how to tell when they’re ready:

The Curly Tendril: Look at the curly tendril closest to the fruit stem. When it turns brown and dries up completely, the melon is usually ripe.
The Ground Spot: Gently lift the melon. The spot where it rests on the ground should change from white to a creamy yellow.
The Sound Test: Thump the melon. A ripe one will have a deep, hollow sound. An unripe melon sounds tight and high-pitched.

Use a sharp knife to cut the stem, leaving about an inch attached to the fruit. Enjoy your harvest soon after picking for the best flavor!

Common Pests and Problems

Stay vigilant for a few common issues:

Aphids & Cucumber Beetles: Blast aphids with water or use insecticidal soap. Hand-pick cucumber beetles or use floating row covers early in the season.
Powdery Mildew: A white fungus on leaves. Ensure good air circulation, water at the soil level, and use an organic fungicide if needed.
Blossom End Rot: A dark, leathery spot on the fruit bottom. Caused by uneven watering which leads to calcium uptake issues. Maintain consistent soil moisture.

FAQ

Can I plant watermelon in July in Southern California?
In most inland areas, yes, but choose a fast-maturing “icebox” variety (under 80 days). It’s a bit late for larger types. Provide ample water to establish plants quickly in the heat.

What is the latest month to plant watermelon?
In inland valleys, early June is generally the cutoff for a reliable harvest before cooler fall weather. In desert areas, a late-summer planting for a fall harvest is possible.

How long does it take for watermelons to grow?
It depends on the variety, but most take between 70 and 100 days from planting to harvest. Always check your seed packet for the specific “days to maturity.”

Can you grow watermelon in pots?
Yes, choose a compact or bush variety and use a very large container (at least 20 gallons). Ensure it has excellent drainage and be prepared to water and feed more frequently.

By following this timing and care guide, you can look forward to a bountiful harvest of homegrown watermelon. The sweet taste of sucess is even better when you’ve timed it just right for our unique Southern California climate.