The category “summer squash” includes yellow squash, patty pan squash and round squash, as well as zucchini, a specialized kind of summer squash. They are easy to grow – the main challenges are pests, diseases and moderating the quantities available. When a succession of healthy plantings can be maintained, these crops can crank out high yields of a vegetable almost everyone likes.
For early crops, look for fast-maturing varieties. We like the green and yellow Zephyr squash, yellow crookneck Gentry squash, (both hybrid bush types), and the yellow Golden Glory and pale green Tender Grey OP zucchini. Squash is one crop where we think it pays to use hybrids. Open pollinated varieties tend to be less predictable, less productive and less reliable.
We were having trouble with Unpollinated Hoophouse Squash. The challenge is that early in spring, there are not many pollinating insects around, and those that are here, are working outdoors and not so likely to find their way into the hoophouse. We largely solved those problems by choosing varieties that are capable of a fair amount of self-pollination, such as the beautiful Golden Glory zucchini and Zephyr, a beautiful bi-color hybrid yellow squash with green ends, which seems better than some squash in self-pollination. It got a low rating in one variety trial I looked at, though it did OK for us.
We have tried growing some annual and perennial flowers in the hoophouse to attract the pollinators in. perennials are more likely to flower at the appropriate time than annuals, even if sown in the fall. We gave up on flowers in pots, as they dry out too fast in the hoophouse.
This spring, with yarrow and shungiku flowering at the right time, we didn’t have many unpollinated squash at all. Is this the secret to early season success with squash?
Sowing for Continuous Harvests
This frost-tender warm weather crop germinates at 60°F (15.5°C) minimum, and does best at 85°F (30°C). Germination takes 5-10 days. During growth the ideal temperatures are 75-85°F (24-30°C) in the day and 65°F (18°C) at night. From sowing to harvest takes 40-50 days. Lilac in full bloom is a phenological sign for the spring being warm enough to direct-sow squash.
Squash plants mature quickly and are then attacked by various insects and fungi, so it makes sense to plant successions every 2-4 weeks until late summer. To make the pest evasion successful, make the sowings in widely separated parts of your farm, and destroy the old sickly plants as soon as the new plants are producing. We plant 6 times during the year, aiming to have a new planting come into production every 25 days, starting 5/15, and ending with the first hard frost.
As mentioned, we transplant our very first summer squash and zucchini (sown 3/1), on 4/1 with rowcover, in the hoophouse. Our first planting outdoors is sown in the greenhouse 3/25, transplanted with rowcover 4/20, about 10 days before the frost date, depending on the weather. Some sources say to sow the second planting a month after frost and the third 3 weeks after the second.
After the first plantings indoors and out, we sow directly in the ground 5 times, 5/24, 6/23, 7/15 and 8/5 (70 days before our average first frost). 8/5 is our last worthwhile planting date. See my post Last Chance Sowings. Also see my post on Succession Planting for working back from your frost date to determine your last worthwhile planting date. Pay attention to the weather as you approach your average first frost date, and be ready to harvest mature crops and protect plants with rowcover. In many parts of the country, a frost or two will be followed by a few more weeks of warm weather, so getting past the first few frosts is worth the effort. It’s easy to get extra harvests for a month or two from mature plants you already have.
See my book Sustainable Market Farming, for more on seed specs, details of sowing, including growing transplants, as well as crop rotations, pests and scheduling succession sowings.
Harvest squash daily to keep them coming
The more you pick, the more you get! Early in the year, growth is slow. We start out harvesting our hoophouse squash and first outdoor squash every other day. Soon we switch to daily harvest (except Sunday). Monday morning squash can be monsters! See Harvesting Squash.
Early on, it’s important that people don’t pick too small. You need to get critical mass to provide enough to sell or cook, or supply your Food Pantry. Harvesting all the squash at 6” or bigger is important. You might choose a smaller size, once the season is underway. Be sure to explain to workers that they should remove and chop up any that are too big to eat. Don’t let monsters take all the energy from the plant. Look carefully.
Avoid harvesting when leaves are still wet with dew (or rain). To preserve the appearance of the squash avoid scratching the skin of the squash on the leaves. One way to do this is to enclose the fruit in your palm as you cut through the stem. Another is to move the spiny leaves out of the way. Yellow squash has thin stems and can be twisted from the plant. Zucchini stems are thick, and need to be cut.
Some people get quite a rash from harvesting these crops, others just get a short-term itchiness that is cured by rinsing arms and hands in cool water. Wear long sleeves for this job, or use special elastic cuffed protective sleeves.
Summer squash will keep 10-21 days (if you are lucky) at 80% humidity and 45°F (7°C). Do not store at lower temperatures or chilling injury can occur. This shows up as a pitted surface which later grows black mold.
Protecting Squash from Pests
One key to reducing pest numbers is to till in old plantings promptly. Flaming is another option (if the soil is too wet to till, for instance).
Squash bugs are probably the most common pest. The adults are long gray insects which emerge from overwintering in wooded areas once temperatures reach about 70°F (21°C). They also drift in on storm fronts. They feed on young seedlings for preference and lay groups of spaced bronze eggs on the undersides of leaves. The eggs hatch in 10 days and the nymphs suck sap from the plants. There are many generations each year and numbers quickly build. Drop hand-picked adults into soapy water rather than crushing them, as the smell of the crushed bugs attracts more. Most summer squash are in the species Cucurbita pepo. Growers with bad pest problems can try Tromboncino squash, a C. moschata squash, or Luffa (vegetable sponge) or Cucuzza (snake or serpent gourd), edible gourds which have more resistance to squash bugs. Be sure to cut them relatively small, while skins can be pierced by a fingernail, for good flavor. These are very vigorous, sprawling plants, which, happily, are also prolific. One option is to plant a row of regular zucchini alternating with these bigger plants – when the zucchini succumb to disease, the sprawlers will take over.
In the hoophouse, we do a daily hunt for striped cucumber beetles (and spotted ones, if we find those). We use some toothed tweezers and do this task first thing, before the beetles have warmed up enough to fly much. They spend the night in the flowers, so are easy to find in the morning. Cucumber beetles spread viral diseases. We reckon if we pay attention to killing off these first-generation beetles, we’ll have fewer throughout the gardens all summer. The hunting season for cucumber beetles here is on average about a month long.
Adult squash vine borers are fairly large orange and black fuzzy moths with glassy black wings. They are active in May and early June here, and there may be a second generation in late July/early August. The small flat brown eggs are laid singly at the base of the stem. The larvae hatch after one week, and are white with a brown head. They spend 4-6 weeks in the stem, eating upwards and growing to 1” (2.5 cm) in size. Then they dig into the soil and pupate for the winter. Plant symptoms include wilting of the whole plant, and stem holes surrounded by frass (caterpillar poop). It is possible to save the plant if you act at the first sign of trouble and pick out the grub, then pile soil over the injury to help the plant recover. Injecting Bt into the stem is another solution. Squash vine borer adults are reputed to be repelled by radishes sown in a 12” (30 cm) diameter circle around each squash plant, or in bands down either side of a row. It’s fine to harvest some of the radishes, but make sure to leave enough that their leaves touch, to provide a continuous barrier. Some growers recommend mixing wood ash or charcoal in the soil with the seeds at planting.
To repel aphids that transmit mosaic diseases, reflective foil mulch can be used. Borage and nasturtium interplanted in cucurbit rows are said to repel insects. They look pretty either way.
Outdoors we use insect netting on hoops over the row, as soon as we have sown the seeds in the ground (or set the transplants). We leave the netting in place until we see female flowers. It may be a surprise to you that there are both female and male flowers. Male flowers have just a thin stem, but female flowers have a miniature fruit behind the flower. Often the first flush of flowers are just males, so you don’t need to worry about those needing visits from pollinating insects. Low temperatures and high light intensity promote female sex expression, meaning that early in a chilly season some varieties of squash produce a lot of female flowers, and no males. Both are needed!
Watch Out for Squash Diseases
See the Squash Variety Trial post for more. Common diseases include Powdery Mildew, Downy Mildew, Anthracnose, Angular leaf spot, Black Rot (Gummy Stem Blight), Bacterial Wilt and various mosaic viruses.