Summer squashes, cucumbers and melons (all members of the cucurbit family) often develop problems during the long hot month of July.
The cause of the primary problem is not always obvious. Insufficient pollination causes small cucumbers and squashes to wither and turn brown. The fruit never fully ripens and there are few if any seeds inside. Honeybees are the principal pollinators of squash and other cucurbits. Bees hide out from the summer heat in their hives or just outside the hives where delegated “fanning” bees create air movement to cool the hive and the other bees. In July, bees forage for pollen and nectar during the cooler morning hours, usually from 7 to 8 a.m., which doesn’t give them much work time.
In the absence of pollinating bees, it’s up to us humans to hand pollinate our cucurbits. First, learn to distinguish between the male and the female flowers. It’s easy. The male flowers appear first and are carried on long, slender stems. The female flowers arrive later to the party. They’re carried on shorter, rounder stems that look like miniature versions of the mature fruit. If insufficient pollination is a problem in your vegetable garden, take a clean artist’s paintbrush to move pollen from the inside of the male flowers to the inside of the female flowers. You’ll need to do this every few days to help with fruit set and it doesn’t always work well.
Make sure that bees have a source of slowly trickling water available nearby – pollinating is thirsty work. A fountain or a temporary spritz from a turned-on hose bib or a drip irrigation system stanchion can attract bees into your garden. It’s too hot now to plant anything, but consider adding a few bee-friendly flowers to your vegetable garden in late August this year and when planting your summer vegetables next season. Any flower with an open daisylike center will attract bees, butterflies and other pollinators. Coreopsis, zinnias, cosmos, and scabiosa or pincushion flower are reliable summer bloomers.
Squash bugs are a common pest insect of cucurbits. Squash bugs, aphids and whiteflies can carry viruses onto cucurbits. Pick off squash bugs and inspect the undersides of leaves daily for shiny reddish brown egg masses. Squish egg masses or wipe them off leaves with a paper towel, wash off aphids with water, use yellow sticky traps to catch whiteflies, and spray insecticidal soaps to smother nymphs. Avoid using broad-spectrum insecticides that kill all insects, pest and beneficial, including bees. Many insecticides cannot be applied when temperatures are above 95 degrees; the products vaporize in the heat and can burn leaves and fruit. Read product labels before application.
High day and night temperatures slow flower production and cause existing flowers to fall off. In July, fruit will reach optimal size in just a few days. Harvest regularly; leaving mature fruit on the vine also slows flower production. Keep the soil consistently moist, but do not fertilize until slightly cooler temps and longer cooler nights arrive in a few weeks.
Send Elinor Teague plant questions at firstname.lastname@example.org or email@example.com (“plants” in the subject line).