Impact of hot, dry growing season on winter and summer squash

It’s all about the birds and the bees

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Q. My squash plants (both summer and winter) have been disappointing this summer. They have produced plenty of flowers, and little squashes have begun to form, but then they discolour and rot away at the far, blossom ends.

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A. This is a common issue, with both summer and winter squash. The cause is that the female flowers have not been pollinated. Without pollination, little squashes begin to grow but then shrivel and fall off.

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Each squash plant bears both female and male flowers. Normally, bees and other pollinators move pollen from the male to the female blooms to begin the pollination process as the pollen moves down to fertilize the female’s ovary.

A lack of pollinating insects is a common cause of failure for squash to develop. The useful work of these insects is sometimes prohibited or at least inhibited by wind, rain, and/or cold — conditions that, even in the presence of pollinators, can affect the pollen’s quantity, quality, and movement into a female bloom. Heat and/or drought can cause blooms to die off quickly, before fertilization can occur.

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The intense heat of mid-May was very hard on many of our young plantings at their most vulnerable, and the growing season in general has been very hot and dry. My zucchini plants struggled to fruit well until I mulched them generously with a nourishing compost and topped the compost with chopped straw to help cool the soil and retain moisture.

Some gardeners, as soon as they see baby fruits forming and then drying off, take on the role of bees by picking a male flower (long straight stem, yellow pollen at centre), pulling back the petals, and dabbing its pollen onto the centre of several female flowers (shorter stem, a small bulge at the bloom base). That little bulge is a baby fruit ready to begin developing once fertilization is complete.

This hand pollinating is too late now for winter squash but not too late for summer squash.

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