Why Your Watermelons Have Stopped Growing—and How to Fix It

Nothing says summer like a juicy, sweet, homegrown watermelon. The classic summertime treat is enjoyed at picnics, barbecues, and outdoor get-togethers, flooding the body with sweet hydration on a hot summer day.

Depending on the variety, it can take between 70 to 130 days to go from planting your watermelon seeds to harvesting the ripe fruit—and if you’ve ever cultivated a watermelon from seed, you know firsthand how rewarding it is to slice into the first melon of the season. Watermelons thrive in hot weather, come in a variety of sizes, and are relatively easy to grow; however, if the growing environment isn’t ideal, you may notice your watermelon struggling.

Although several factors can contribute to stunted watermelon growth, such as pests, poor soil drainage, and lack of sunlight, with a few adjustments you can bring your slow-growing melon back to health. Ahead, our experts share helpful solutions to take your much-anticipated watermelon from stunted to stunning.

Why Are My Watermelons Not Growing?

If you’ve noticed your watermelon has stopped growing, panic may set in. The good news is that when it comes to the stunted growth of watermelons, it can be easy to locate the root cause. And if caught early enough, there may be time to fix it. Here are the most common reasons why your watermelon quit growing and how to ensure a big, juicy watermelon from the garden.

Inadequate Sunlight

Watermelons thrive in full sun and need at least 8 to 10 hours of sunlight per day. "Plenty of sunlight is required to encourage the plants to grow, flower, and attract the pollinators," says Joanie Ingram, master gardener of Hutchings Greenhouse. "Once pollinated, the developing fruit needs the sunlight to maximize the sugar content in the melon." Although the plants can tolerate some partial shade in hotter climates, Ingram says that insufficient light leads to fewer blossoms and fruit yield.

How to Fix: If possible, trim nearby trees or shrub branches that may be blocking the sun. If that’s not doable, next planting season, choose a sunny location with adequate sunlight.

Poor Soil Quality

"Watermelons thrive in fertile, nutrient-rich, well-draining soil with a mildly acidic to neutral pH level of 6.0 to 6.5," says Ingram. Heavy or clay-like soil can slow the growth of the watermelon because it doesn't allow proper drainage. Watermelon is also a heavy feeder and needs proper nutrients in the soil to grow to its full potential. When soil is infertile or sitting at the wrong pH level, this can cause stunted growth of the overall plant.

How to Fix: To improve soil fertility, you can incorporate organic matter such as organic compost, worm castings, or organic fertilizer. To understand the complete makeup of your soil condition, you can perform a simple soil test. You can also call your cooperative extension for instructions.

Lack of Pollinators

Many plants use pollen to produce fruits and seeds. Without proper pollination, those plants will not produce their crops. "Pollen from the male flower needs to be moved to the female flower, and once the female flower has been fertilized, a watermelon will develop," says Ingram. It then takes about a month for the melon to grow and ripen. If your garden lacks pollinators, it will also lack food.

How to Fix: Attract pollinators (like bees) to your garden by planting flowers that they can’t resist. Marigolds, lavender, borage, nasturtium, and zinnias are loved by pollinators. "Another option is to manually pollinate your plant," Ingram says. This is done by removing a male flower and rubbing the pollen from the male blossom onto the stigma of the female flower. Doing this will ensure proper pollination and continued growth of your plant. The female flowers have small, round pods at their stems (they look like tiny watermelons), while the male flowers have long, slender stems.

Not Mulching

"Mulching is an extremely easy way to improve your garden beds instantly," says Eric Nieusma, an organic and regenerative farmer and co-owner of Maine Hill Farm. "Mulching helps maintain proper moisture, reduces watering, attracts helpful worms, suppresses weeds, warms the soil, and keeps the vine and fruits off the direct soil where they are susceptible to certain diseases." Without it, your melon could begin to struggle in size and health.

How to Fix: "Mulch can be produced for free using grass clippings or fallen leaves or by purchasing inexpensive hay or straw, or using a black plastic mulch designed specifically for row crops,” says Nieusma. If using hay, straw, or grass clippings, Nieusma recommends applying 4 to 8 inches of mulch over the entire garden bed, leaving a little space around the base of plants.

Irregular Watering

During the growing season, it’s important to provide your watermelon with ample water, as the plant has high water requirements. If you’ve overwatered or underwatered, you may notice stunted growth, wilted leaves, and an overall unhappy-looking plant.

How to Fix: Irrigation is important. "Keep the soil moist but not waterlogged," says Ingram. "Water the base of the vines in the mornings and try to avoid wetting the leaves or overhead watering." A solid rule of thumb is to aim for an inch of water per week, with more frequent watering during hot weather or drought conditions. If watering by hose, Nieusma encourages you to count the seconds it takes to fill a one-gallon container (you can use a timer) for your reference. This will give you a rough idea of how many gallons you are giving your plants each watering.

Pest Damage

Watermelon plants can be susceptible to various pests that negatively affect their health and growth. Cucumber beetles, rind worms, and aphids (to name a few) can wreak havoc on your melon plant fast.

How to Fix: Inspect your plant regularly. Check under the leaves for bug infestation and look for signs the plant is under attack, such as bite marks, discoloration, or wilting leaves. If you see signs of pests, Nieusma recommends treating plants with appropriate botanical pesticides, essential oils, or natural soap recipes. 

Cold-pressed neem oil is a natural, safe, and effective form of pest management. You can mix equal parts neem oil and natural soap as recommended. "Use lukewarm water, and spray the undersides of leaves around sunset or early evening, when the sun will not be hitting the plant," says Nieusma.

Tips for Growing Big, Juicy Watermelons

Now that you know what could be causing your watermelons to become stunted, take our experts' advice for growing a successful crop of watermelons in your garden.

Select the Right Variety

You can ensure a successful watermelon crop by purchasing watermelon seeds or seedlings that are best suited for your growing zone. "Note the days of maturity are from the date of transplanting not seeding," says Ingram. "Add 10 more days if direct sowing."

Space Plants Properly

A planting area at least 4 feet by 6 feet gives larger watermelon varieties the space to sprawl out without overcrowding.

Fall Cover Crop for Soil Health

Cover cropping is a gardening technique where you plant a diverse mix of crops in your garden bed that you will simply let die in place when winter comes. "Cover cropping your garden beds in the fall will provide the soil and future crops with essential nutrients and organic matter for spring planting," says Nieusma.

Early Pest Prevention

Prevention is the best method to control pests. "Start treating before you see them," says Nieusma. Adding a row cover over your plants will aid in extra pest protection.

Transplant at the Right Time

"Wait until the temperature of the soil is approximately 70 degrees or warmer before transplanting watermelon plants outdoors or planting seeds," says Ingram, as cold temperatures can inhibit
plant growth.

Use a Biodegradable Pot When Starting Seeds Indoors

Watermelons have sensitive root systems, leaving little room to mishandle when transplanting outdoors. When starting plants early indoors, Nieusma recommends using biodegradable pots as you can plant the pot directly into your garden, leaving the melon’s root system undisturbed.

Know When to Harvest

First, know the date to maturity for your variety. Then, when they’re ready for harvest, you’ll see white or yellow coloring on the underside of the melon, the color of the rind will go from shiny to dull, and you’ll notice a brown tendril spot where the stem meets the watermelon. If you tap the fruit, it should sound hollow. All these indicators point to full maturity. "Harvesting melons too early results in smaller fruits that lack flavor," says Nieusma