How To Grow Healthy Squash Plants

If you planted summer squash in your garden this season, you know that, when healthy, it is a very generous plant. Whether you started from seeds or planted three or four baby plants, you are probably already eyeing your garden plot, wondering if your backyard will soon be overrun by crookneck and zucchini vines. Squash is incredibly easy to grow but, even though you planted in rich soil, fertilize on the recommended intervals, mulch and keep roots moist, you may still run into a few problems. Read through this list to diagnose your squash and zucchini issues and learn how to solve common problems.


During excessive rainy spells in the summer months, squash can develop botrytis, or gray mold. It usually occurs when dead blossoms start to rot in rainy, humid weather. If you run across gray mold on your squash, cut the stems and toss them into the compost pile. During prolonged rainy spells, rake up fallen blooms to reduce the chances of the disease developing.

Blossom End Rot

Those sunken dark spots on the bottom of squash are called blossom end rot (BER for short). It’s not a disease but a sign of calcium deficiency an occurs due to uneven watering (wet-dry cycles in the soil), root damage, or too much nitrogen in the soil. You can still eat squash with BER however, simply cut away the sunken area. Treat plants with a calcium spray specifically designed for BER, keep soil consistently moist, and mulch around the plants.

Wilting Leaves

Soil may have adequate moisture but, during midday heat, squash leaves can still tend to wilt. Squash vines have a lot of leaf area to support, and during the hottest part of the day, it’s common for leaves to wilt. (Many plants, including hydrangeas, wilt in the middle of the day and revive as the evening cools.) Instead of immediately reaching for the garden hose and watering, check the plants again in the early evening to see if leaves have revived. Remember to mulch around the base of vines to help retain soil moisture.

Brown and Crispy Leaf Edges

When young leaves on squash vines develop brown, crispy edges, there’s a possibility you are dealing with pesticide damage. Quite often a pesticide is applied when the plants are too young and not able to tolerate the chemicals; the vine never outgrows the damage, remains stunted, and may never bear fruit. Always use extreme caution when applying pesticides and follow label directions exactly.

Squash Vine Borer

When squash vines wilt overnight, you have probably been invaded by the squash vine borer. The adult red and black flying insects lay eggs on the base of vines and undersides of leaves. Squash vine borers can infest a plant so heavily that they’ll tunnel into fruit through the stem, but as the growing season comes to a close, borers will burrow directly into fruit. Small holes in the sides of squash are likely a clue that a borer hides inside.

The easily visible borer eggs are tiny red specks—look for them on vines and undersides of leaves, pluck them or scrape them off and squish them whenever you find them. If vines wilt, yank them up, cut them open and look for borers. Never put borer-infested vines into your compost – burn them or bag them and put them in the garbage.

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Powdery Mildew

Late in the growing season, a white powdery substance often shows up on squash leaves. This is powdery mildew, a fungus disease. Once started, a fungicide spray can control it but can’t cure it. Many other plants, including bee balm, lilac and garden phlox, also get powdery mildew and create a source of infection. As powdery mildew disease progresses, leaves will first become completely white, then turn ashen gray. Ultimately, leaf sections between the veins fall away, creating a raggedy appearance. When the growing season ends and it is time to pull the vines, gather as much of the infested plant material as you can and destroy it; do not toss it in the compost pile.