9 Watermelon-Growing Problems To Avoid This Summer

With so much space and time spent developing healthy, delicious watermelons, avoiding common growing problems is key. Some issues pop up as a response to cultural conditions, while others may be a case of being in the wrong place at the wrong time. Simple measures, like harvesting at the right time, bring about the tastiest fruits.

Setting the vines up for success includes meeting their preferred growing requirements and preventing intruders like pests and diseases. Companion plants and attracting pollinators to the garden also help.

Beautiful vines full of sweet rewards are within reach. Growing your own makes them that much sweeter, but be sure to avoid these common watermelon problems to ensure the best yields:

Misshapen Fruits

Sometimes, watermelons flower and then produce odd-looking or poorly-shaped fruit. These oddballs are often due to poor pollination. 

The melons produce male and female flowers and rely on insects for pollination and regular fruiting. Unpollinated flowers produce underdeveloped fruits. 

To enhance pollination, you can opt for hand-pollinating, using a toothbrush or paintbrush to pollinate the blooms. For best success, grow flowering plants nearby to attract bees and insects. Nectar-rich blooming herbs, perennials, and annuals draw more flying pollinators, who will, in turn, visit the watermelon blossoms.

Cracked Melons

It’s disheartening to find a near-ripe watermelon cracked. The joy of growing and watching the melons develop is easily undone by a bursting rind.

To avoid cracking, cut back irrigation when fruits are nearly ripe. As they reach full development, the fruits stop growing in size but continue to absorb water. At already 92% water, the extra moisture surpasses maximum capacity, and the rinds split open.

Adding water also reduces sweetness. As the melons ripen and reach their sugar content, extra water dilutes the concentration, leading to a less sweet taste. While the vines continue to need regular water, decreasing it just before harvesting helps prevent cracking and splitting.

Slow Start

Vines that are slow to develop may relate to planting issues and cultural requirements. Melons are slow to mature, at around 65 to 100 days from sowing, but they’ll continually grow long, leafy vines in the right conditions.

At planting, amend the soil with compost or other organic matter to ensure it’s organically rich. This crop needs well-draining soils to thrive and prefer a sandy loam. The proper soil sets the foundation for plant health.

With the soil in check, the next measure is sowing and transplanting at the appropriate temperature. Watermelons are heat-loving and need warm soils for germination. They also require full sunlight for growth. Temperatures above 70℉ are optimal. 

When planting, ensure the soil temperature is above 65℉. Long summer days and warm nights promote vigorous plants. Soils that are too cool at sowing hinder germination, and seedling growth may be slow to start.

Provide consistent moisture throughout the growing season. One to two inches a week, including rainfall and irrigation, is usually sufficient. Fluctuations in water cause plant stress and many problems with watermelon fruits, leading to halted growth and lower quality yields. Remember to ease the watering schedule when fruits are nearly full size.

Grow the cucurbits in mounds to promote drainage and airflow. Two to three vines planted in low mounds at 16 inches tall give vining stems room to run while elevating the crown. Provide straw or mulch around the crowns to retain moisture and regulate soil temperatures.

Leafy Vines, No Fruits

Avoid overfertilizing with too much nitrogen. Nitrogen produces leafy vines but reduces flowering. The plant directs energy into foliage and stem growth rather than fruit production. Opt for a fertilizer higher in phosphorus (the K in the N-P-K fertilizer ratio) to promote flowering. 

Phosphorous and potassium are necessary for flowering and fruiting. While nitrogen is needed early on as plants establish, an overage is too much of a good thing. Avoid applying excess nitrogen through manure and compost during the growing season.

Small Fruits

Unless you’re growing a dwarf or mini variety, petite fruits may indicate crowded conditions. There may also be too many fruits per vine.

Overcrowding results in competition for resources and a lack of air circulation, which affects plant vigor. Grow two to three plants per mound, with six to seven feet between mounds for vines to run. Roots and vines need not compete for moisture or sunlight. Diseases from damp and crowded leaves are less likely.

Too many fruits per vine mean plants can’t support the energy they need to develop fully. Two to four melons per vine are common, especially for large varieties (two) and small melons (four). Thin fruits if you have prolific small, uncharacteristic fruits.

Harvesting at the Wrong Time

There’s a sweet spot for harvesting watermelons for maximum flavor and texture, but many beginners face problems when it’s time to pick. While some crops continue to ripen after picking, these melons only ripen on the vine.

They won’t continue to develop flavor or increase sugars post-harvest. An underripe melon will be pithy, less color-rich, and less sweet and juicy. An overripe one may be mushy and off-flavor.

Count out the days to mature fruits from your sowing date to gauge readiness. The seed packet indicates this as “days to maturity” or “days.” The melons usually mature in 65 to 100 days, depending on the selection and weather. Maturity is about 35 to 45 days after flowering.

Fruit Rot

Rotten watermelons are very disappointing, but this problem is easily preventable with mulch. Protect the large rounds while growing to peak ripeness, cradle them in straw to elevate them from the soil level. Ideally, this lessens moisture and improves circulation while insulating the fruit. It also forms a barrier between soil-dwelling pests.

If you’re checking a ripening melon and notice a rotting patch at the base, this is blossom end rot. In the same way, it affects tomatoes, melons can look perfectly healthy until suddenly they begin to rot.

Blossom end rot occurs from water fluctuations—extreme moisture and dryness cause a lack of nutrient uptake, including calcium. Calcium is necessary to prevent blossom end rot. At planting, scatter crushed eggshells or bone meal to promote calcium availability. Water consistently to avoid fluctuations.

Soil pH is another factor in calcium absorption. Soils with a low pH or high pH may inhibit availability. In the fall, amend with garden lime or sulfur, depending on a soil test, to reach slightly acidic soils for watermelons (around 6.0 to 6.5).

Sudden Wilt

If leaves or vines are wilting, the first thing to check is soil moisture. If the soil feels consistently moist (not overly saturated and not dry), then the wilt has an underlying cause.

Fusarium and Verticillium wilt are fungal diseases that cause wilting leaves, blackened leaves and stems, and plant decline. They spread from spores in the soil and can come with infected seeds or transplants.

Wind, water, and garden tools also spread the spores. The fungus impacts the roots and affects nutrient and water uptake. With fungal wilts, you may see one half of the plant wilting more than the other.

Unfortunately, there’s no treatment for wilts. Remove and dispose of affected plants, keeping them out of the compost pile. Grow disease-resistant varieties to limit the spread.

Another cause of quick wiling may be due to squash vine borers. The adult insects are moths that lay a single egg along the stems. Larvae hatch and burrow into the stem to feed on plant tissues. Unable to absorb water, the vine suddenly wilts. There are ways to lessen the borer’s damage, the best being regular scouting and growing melons away from other cucurbits in infested areas.

Leaf Damage

As members of the Cucurbitaceae family, watermelons are susceptible to the same pests as squash, cucumbers, cantaloupes, and pumpkins. These include the cucumber beetle, the squash vine borer, and the squash bug.

Each of these pests feeds on plant parts and causes damage. While watermelons aren’t their primary host, they won’t resist the opportunity to feed on them. 

The squash bug is a sap-sucking pest that causes leaves to lose water and nutrients. The leaves become speckled, eventually wilting, blackening, and dropping.

Cucumber beetle adults feed on leaves, blossoms, and fruits, while larvae feed on roots and stems. In other cucurbits, they spread bacterial wilt. Fortunately, research shows that watermelons are resistant to this type of wilt.

Regular scouting for each pest benefits the crop. Pyrethrin sprays help treat the squash bug and cucumber beetle.

Disease is another cause of leaf damage. If you notice distinct yellow and brown spots, you may be dealing with anthracnose, a common leaf blight. Fuzzy, powdery spores on the undersides of leaves and yellow upper speckling indicate powdery mildew or downy mildew. A horticultural oil like neem can stave off early infections.

Prevention through cultural management is the best means of defense. Provide plenty of air circulation around vines to avoid damp conditions. If disease is a problem, avoid splashing the leaves through irrigation. Water at the ground level through drip irrigation or soaker hoses to avoid overly wet conditions and spreading the spores through splashing water. Disinfect tools after pruning diseased plants.