Looking Ahead to June: Growing Summer Squash

The bold foliage of two different summer squash varieties.

The bold foliage of two different summer squash varieties.

Summer squash are always a part our vegetable garden from June through mid-October.  We enjoy their reliability, their prolific nature, their bold foliage, and the immense selection of varieties from which to choose each year.  And we love to eat the fruits, slicing a sweet nutty cousa, such as the variety “Magda”, into salads, shredding yellow crooknecks for breads and cakes (see recipe below), or stir-frying a sliced patty pan with potatoes and onions.

Given warm, well-drained soil with plenty of organic matter, summer squash is easy to grow and prolific, each plant producing

Summer squash types (left to right): patti pan, cousa, yellow zucchini, green zucchini.

Summer squash types (left to right): patti pan, cousa, yellow zucchini, green zucchini.

dozens of small immature fruits, the stage at which they should be harvested.  We start the early summer crop from transplants, then sow seeds in late August for a fall crop that will stay productive until the first light frost.

You cannot have too much organic matter in the soil for summer squash, so we always add more when planting, either worm compost or composted goat manure.  We also mulch the soil in the squash beds with organic matter that will rapidly decompose, such as composted manure or shredded leaves.

A cutworm collar made from rolled strips of newspaper should be wrapped around the young succulent stems of transplants.  And because squash seedlings, with their large seed leaves (cotyledons), are a favorite of slugs, we keep a continuous ring of wood ashes around the perimeter of each bed (adding more after a heavy rain) until the plants have several true leaves and the stem is toughened.  The leaves and stems develop spines as they mature, and when that happens the slugs leave them alone.

Keeping Squash Plants Productive

Powdery mildew on cucurbit leaf.

Powdery mildew on cucurbit leaf.

As summer heat and humidity intensify, check your squash plants regularly for signs of blossom blight and powdery mildew.  Blossom blight appears as fuzzy growth on the spent blossoms at the tips of fruits, and, left unchecked, it can lead to rotting of the fruit.  To avoid this problem, provide good air circulation by wide spacing at planting time and keeping the planting area free of weeds.  If necessary, thin excess foliage on overcrowded plants.

In late summer, when the weather turns hot and humid, the powdery mildew fungus attacks the older leaves of summer squash (as well as cucumbers and winter squash), turning them white.  Again, plenty of air circulation is the key to minimizing this problem.  You may be able to prevent powdery mildew from infecting squash plants with weekly sprayings of baking soda solution made with one tablespoon of baking soda per gallon of water, adding a half teaspoon of liquid dish soap as a spreader-sticker.  Apply this concoction once a week, beginning in mid-summer, and only on well-watered plants.  Spray the plants early in the day, not in full sun.  Discard any unused solution.  Try the solution on a few leaves first to make sure your variety of squash is not super-sensitive.

Sudden wilting of squash vines is the first symptom of squash vine borer invasion.  A hole at the base of the vine that leaks a wet sawdust-looking frass is conclusive evidence – this is where the fat grub-like caterpillar (the larva of a moth that looks like a wasp) made its entry.  Your only recourse to save the patient is immediate surgery.  Starting at the entry hole, slit the stem longitudinally through the top epidermal layer with a sharp razor blade or knife, extending the cut until you find the borer.  Remove and dispatch the borer, then pack the damaged area of the stem with moist soil to promote root development.  With a little luck, the patient will live to bear fruit.  Sowings of summer squash late June (Zones 6 and 7) or early July (Zones 4 and 5) are good insurance against an outbreak of squash vine borers.  The female moth has stopped laying eggs by these later sowing dates.

Striped cucumber beetle in squash blossom.

Striped cucumber beetle in squash blossom.

Striped cucumber beetles are a scourge in some years, feeding on all types of cucurbits and spreading bacterial and viral diseases as they feed on all parts of the plant.  Hand-picking may keep them at tolerable levels if done in early morning – like me before morning coffee, they are lethargic and easier to subdue than later in the day.  Sucking up the beetles with a portable vacuum, again early in the morning, also works.

Squash Sex

I am often asked to explain why the early squash flowers never produce fruits, even when there are plenty of bees around.  The answer is a short course in cucurbit sex.

Female squash blossom.

Female squash blossom.

All cucurbits, including summer squashes, are monoecious plants with imperfect flowers, meaning flowers of both sexes can be found on the same plant.  The first flowers of the season are typically all male, incapable of producing fruits.  Once you know what to look for, you can easily sex a squash blossom.  Female flowers have a slightly swollen ovary at the bast of the petals; if both pollination and fertilization occur, this ovary will swell and become the familiar squash fruit.  Male flowers lack this conspicuous feature.

Male squash blossom.

Male squash blossom.

Why would  a plant invest energy in producing only male flowers?  I’ve never heard or read an explanation, but I have a theory.  Cucurbits depend on bees to transfer pollen (the sperm-producing structure) of male flowers to the stigma (gateway to the ovary) of female flowers.  Perhaps production of the early pollen-loaded flowers serves to attract a resident population of pollinators before the plant invests energy in producing flowers that must be pollinated.

 
Summer Squash Bread
Ingredients:
2 eggs, beaten
1 1/3 cup sugar
2 teaspoons vanilla
3 cups grated fresh yellow crookneck or cousa squash
2/3 cup melted unsalted butter
2 teaspoons baking soda
Pinch salt
3 cups all-purpose flour
1/2 teaspoon ground cloves
2 teaspoons cinnamon
1 cup chopped pecans or walnuts (optional)
1 cup dried cranberries or raisins (optional)

Preheat the oven to 350°F (175°C). In a large bowl, mix together the sugar, eggs, and vanilla. Mix in the grated squash and then the melted butter. Sprinkle baking soda and salt over the mixture and mix in. Add the flour, a third at a time. Sprinkle in the cinnamon and nutmeg and mix. Fold in the nuts and dried cranberries or raisins, if using.

Divide the batter equally between 2 buttered 5 by 9 inch loaf pans. Bake for 1 hour (check for doneness at 50 minutes) or until a wooden pick inserted in to the center comes out clean. Cool in pans for 10 minutes. Turn out onto wire racks to cool thoroughly.

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About Reeser Manley

I was born in Laramie Wyoming but moved to the southeast at an early age. I was educated through my B.S. in Biology in the Columbus, Georgia area, then crossed the Chattahoochee River to earn my M.S. in Botany at Auburn University. For the next ten years, I worked as Horticultural Manager for the George W. Park Seed Co. in Greenwood, S.C. At 40 years of age, I decided to return to graduate school and in 1994, I earned a Ph.D. in Horticultural Science from Washington State University, Pullman, Washington. Fast forward through 10 years at university (7 at UMaine, Orono) and you find me teaching high school science in Eastport, Maine, the edge of the world, and writing a weekly garden column for the Bangor Daily News. My new book, The New England Gardener's Year, a Month-by-Month Guide for Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, and Upstate New York”, will be published later this year by Cadent Publishing. You can learn more about the book by visiting its Facebook page: http://www.facebook.com/pages/The-New-England-Gardeners-Year/187285218055676.)