When To Plant Watermelon In Missouri

If you’re planning to grow watermelon in Missouri, getting the timing right is your first step to success. Knowing exactly when to plant watermelon in Missouri makes all the difference between a bumper crop and a disappointing harvest. Our state’s unique climate, with its hot summers but unpredictable spring frosts, requires a careful approach. This guide will walk you through the optimal schedule and tips to get your melons off to a strong start.

The optimal time for planting watermelon in Missouri is after the last spring frost, when soil temperatures have reliably warmed. For most of the state, this means aiming for mid-May. In the warmer southern regions, you can often plant in late April. In the cooler northern parts, it’s safer to wait until late May. Always check your local frost dates, as a late cold snap can set young plants back significantly.

Understanding Your Missouri Growing Zone

Missouri spans USDA plant hardiness zones 5b to 7a. This range affects your specific planting window.

Zones 6b & 7a (Southern MO): Last frost is typically around April 15. You can plant seeds or transplants from late April to early May.
Zones 5b & 6a (Central & Northern MO): Last frost dates hover around May 10. Target planting from mid to late May here.
Zone 5b (Far Northwest MO): Frost risk can last until mid-May, so planting in late May is the safest bet.

When in doubt, waiting an extra week for warm soil is better than rushing and losing plants to chill.

The Critical Role of Soil Temperature

Watermelons are tropical plants that despise cold feet. Air temperature is less important than soil temperature at planting time.

Ideal Soil Temp: A consistent 70°F (21°C) or warmer.
Minimum Soil Temp: Never plant below 60°F (16°C). Seeds will rot, and transplants will stall.
How to Check: Use a soil thermometer at a depth of 4 inches, taken in the morning for an accurate reading.

If your calendar says “go” but your soil is still cool, hold off. Black plastic mulch laid a week or two before planting can help warm the soil faster.

Starting Seeds Indoors vs. Direct Sowing

You have two main options for getting your watermelons growing. Each has it’s own advantages.

Starting Watermelon Seeds Indoors

This method gives you a head start, especially in northern Missouri.

When: Start seeds indoors 3-4 weeks before your expected outdoor planting date.
How: Plant 2-3 seeds per biodegradable peat or cow pot. They hate root disturbance.
Care: Provide plenty of light and keep them warm (75-80°F). Thin to the strongest seedling.
Transplanting: Harden off seedlings for a week before moving them outside permanently.

Direct Sowing Seeds in the Garden

This is often simpler and avoids transplant shock, but requires patience for warmer conditions.

When: Once all frost danger is past and soil is above 70°F.
How: Plant seeds 1 inch deep in small hills or rows. Sow 4-6 seeds per hill.
Spacing: Space hills 6 feet apart. Once seedlings emerge, thin to the 2-3 strongest plants per hill.

For most gardeners, direct sowing is the easiest path if you can wait for the soil to warm.

Choosing the Right Watermelon Varieties for Missouri

Selecting a variety suited to our climate ensures a better chance of ripening before fall frost. Look for varieties with shorter “days to maturity.”

Early Season (70-80 days): ‘Sugar Baby’, ‘Golden Midget’, ‘Blacktail Mountain’. Perfect for shorter summers.
Mid Season (80-90 days): ‘Crimson Sweet’, ‘Charleston Gray’, ‘Moon and Stars’. A reliable choice for most of the state.
Long Season (90+ days): ‘Jubilee’, ‘Allsweet’. Best for southern Missouri with a long, hot growing season.

Consider disease resistance too. Many modern hybrids offer resistance to common fusarium wilt or anthracnose.

Step-by-Step Planting Guide

Site Selection: Choose the sunniest spot in your garden—watermelons need 8+ hours of direct sun daily.
Soil Preparation: Work in 3-4 inches of compost or well-rotted manure. Soil should be well-draining and have a pH of 6.0-6.8.
Planting: For transplants, set them in the ground at the same depth they were in the pot. For seeds, plant 1 inch deep.
Watering In: Water thoroughly after planting to settle the soil and eliminate air pockets.
Mulching: Apply straw or black plastic mulch around plants to conserve moisture, suppress weeds, and keep soil warm.

Caring for Your Watermelon Plants

Consistent care through the summer is key to sweet, juicy fruit.

Watering: Provide 1-2 inches of water per week. Water deeply at the base, avoiding wetting leaves. Reduce watering as fruit ripens for sweeter melons.
Fertilizing: Use a balanced fertilizer at planting. Switch to a low-nitrogen, higher-phosphorus fertilizer when vines start to run to encourage fruit set.
Weeding: Weed carefully when plants are young. Once vines spread, their dense foliage will shade out many weeds.
Pest Watch: Keep an eye out for cucumber beetles and squash bugs. Row covers early in the season can help, but remember to remove them for pollination.

Signs Your Watermelons Are Ready to Harvest

Harvest time is the best reward. Look for these clues about 80-90 days after planting, depending on your variety.

The curly tendril closest to the fruit stem turns brown and dries up.
The spot where the melon rests on the ground changes from white to a creamy yellow.
The rind loses its glossy shine and becomes dull.
You hear a deep, hollow thump when you tap it (this takes some practice).

Use a sharp knife to cut the stem, leaving an inch attached to the fruit. They don’t continue to ripen off the vine, so timing is crucial.

Common Challenges and Solutions

Even with perfect timing, you might face a few hurdles.

Poor Fruit Set: This is often due to lack of pollination. Encourage bees by planting flowers nearby, or hand-pollinate female flowers using a male flower.
Blossom End Rot: Dark, sunken spots on the fruit bottom are caused by calcium uptake issues, usually from irregular watering. Maintain consistent soil moisture.
Vines Flowering But No Fruit: Early flowers are often male. Female flowers (with a tiny fruit at the base) will appear shortly after. Be patient.

FAQ: Planting Watermelons in Missouri

Can I plant watermelon seeds in June in Missouri?

Yes, but choose an early-maturing variety (70-80 days). Planting in early June in central or southern Missouri can still yield a harvest before the first fall frost in October.

What is the latest date to plant watermelons in Missouri?

Aim to plant by late June at the absolute latest. You need to count back from your area’s average first fall frost (mid-October for most areas) using the “days to maturity” on your seed packet.

How long does it take for watermelons to grow?

From planting to harvest, most varieties take 80-100 days. Smaller, icebox types can be ready in as little as 70 days, while large picnic types may need 90+ days of warm weather.

Should I start watermelon seeds indoors for a Missouri garden?

It can be helpful in northern Missouri to extend the season. In central and southern Missouri, direct sowing once the soil is warm is usually sufficent and less risky for root disturbance.

Getting your planting timing correct is the most important factor for growing watermelons in Missouri. By waiting for warm soil, choosing a suited variety, and providing consistent care, you’ll be well on your way to enjoying homegrown sweetness all summer long. There’s nothing quite like the taste of a melon you nurtured yourself from a tiny seed.