Edibles

Squash (Summer): Sow and Grow Guide

Squash (Summer): Sow and Grow Guide

From long, green zucchini to yellow saucer-shaped patty pans, summer squash is extremely versatile in the kitchen—it can be sautéed, steamed, baked, or grilled. You can also add squash to omelets, soups, casseroles, lasagna, shish kebobs, sweet loaves (zucchini bread), or serve by itself. Summer squash’s tender texture and buttery flavor is the stuff culinary dreams are made of. Luckily, they’re pretty simple to grow! Most summer squash plants grow in a bush form, and the fruits are harvested young when their outer skin is still soft, and seeds are immature. Summer squash’s storagegrown at home can store in the refrigerator for about a week and a half so enjoy shortly after harvest.

Did you Know? Summer and winter squashes are closely related, and in some cases summer squash matures into winter squash. They have similar growing instructions and are afflicted by the same pests, too. They are, of course, different in growth and fruit. The word squash comes from the Narragansett Native American word, askútasquash, which means “eaten raw”, even though these days we most often cook squash.

GENERAL SOWING

When to sow outside: RECOMMENDED. 2 to 4 weeks after your average last frost date, and when soil temperatures have risen to 70°–85°F.
When to start inside: Not recommended except in very short growing seasons, 2 to 4* weeks before transplanting. Use biodegradable pots that can be planted directly in the ground, minimizing root disturbance. *Be cautious to not mature seedling over 4 weeks as plants become stressed and potentially stunted.

How many do I plant?
Summer squash are possibly the most productive plants in the summer garden. One plant generally produces enough fresh squash for 2 people to eat all summer. Summer squash can be cut into strips and used as a gluten-free, raw noodle substitute or pickled and canned, too. It may also aid in making friends with some neighbors by sharing the bounty.

INDOOR SOWING
If you have a shorter growing season, you may consider starting your squash seeds indoors. Use a lightweight seed starting mix/media (sterile, and lighter than potting mix), and sow summer squash seeds 1/2”–1" deep, and winter squash 1” deep. Sow 2–3 seeds per pot, thinning to the strongest plant once leaves appear (clip extra plants at the soil level using scissors). The strongest plant may not be the tallest; look for thick, strong stems and deep color. By thinning early, you minimize the negative impact of crowding, like stretching for light. Read more indoor sowing tips.

Containers
Sow in 3”–4” biodegradable pots that can be planted directly into the ground, minimizing root disturbance. Biodegradable paperboard pots are the ideal size, easy to label, and convenient for sharing plants with friends. Squash roots are sensitive to transplanting, which is why direct sowing is our recommendation.

Transplanting
Harden off seedlings after 2 ½ to 3 weeks. Hardening off is the 7 to 10 day process of introducing pampered seedlings to the intense outdoor sun and temperature swings. Read more about hardening off.

Transplant into an area of full sun (6 or more hours a day), when soil temperature is at least 60°F. If you don’t have a soil thermometer, this is often about 2 weeks after your last frost, but double-check the weather forecast. Transplant on a cloudy day or in the evening to reduce stress.

Remove the bottom of the biodegradable pot when transplanting into the planting hole. This allows roots to escape easily while the remainder of the pot breaks down.

OUTDOOR SOWING

Sowing or transplanting preparation and spacing
Amend the soil ahead of time. We suggest submitting a soil test periodically, which gives you detailed information on your soil and how to improve it. Over-fertilization can invite pests, reduce fruit yield in favor of leaf growth, impact flavor, burn plants, or be a pollutant. Work soil so it is clump free, allowing it to drain well, and apply any additional fertilizer and/or organic matter needed. Initially, you just want the plants to grow, so usually a balanced fertilizer is best.

Summer squash is commonly grown in mounds 3’–4’ apart. Raised mounds warm the soil more quickly in spring, and drain well. Vining summer squash can be grown on a trellis to save space, and increase airflow, which helps prevent fungal disease. If you choose to grow on a trellis, plants may be spaced more closely (half spacing). Grab some ideas on trellising from our tomato trellis blog.

Weeding
Keep areas weed-free, but cultivate shallowly as to not disturb shallow squash roots.

Fertilization
Once your plants are almost ready to produce flowers and fruit, you can apply a phosphorous-rich liquid fertilizer to encourage blooming. Apply 4 weeks from transplant, or 6 weeks from seedling emergence if direct sown, repeating monthly. However, we always recommend a soil test to check for phosphorous levels first.

Water
It is normal for squash leaves to wilt in the heat of the day and recover overnight; it’s their way of conserving water. To know if your plants need water, poke a finger into the mound, if you feel moist soil 2” down you can wait to water, but at about 3” go ahead and water. Avoid watering the leaves of the plant as it can encourage powdery mildew, a fungal disease that attack the plant leaves.

POLLINATION

Both summer and winter squash have separate male and female flowers on the same plant (“monoecious”). Bees are needed to transfer pollen from the male flower to the female flower, which produces the fruit. Male flowers appear earlier in the season than female flowers, in theory to attract bees to the area, so don’t be alarmed if the first flowers do not produce fruit. Squash, as a native, has co-evolved with native “squash” bees. Squash bees are ground nesting and you can create habitat for them by leaving a weed-free dirt patch open and unmulched. Native squash bees are active earlier in the morning than the European honeybees and are also superior pollinators. Squash bees are focused on collecting pollen from all the flowers on the squash plants vs. the honeybee, which will collect pollen from many plants and may go to a few squash flowers and be distracted by another flowering species. Because squash bees are focused on squash, they ensure more female flowers are pollinated completely, resulting in more and better-shaped fruit.

If you’re not seeing any bees, sow bee-attracting flowers that bloom in early summer, like borage or alyssum, near squash plants. If bees continue to be few and far between, hand pollinating may be necessary. Use a paintbrush, or remove one male flower and press it into female flowers (one male flower can be used on up to 10 female flowers). (More about hand pollination)

Since squash are so dependent on bees, take extra precaution in applying any pesticides (organic or otherwise). Do not apply pesticides to flowers, and apply very early in the morning or late in the evening when bees are less active; if you have native squash bees, evening may be best.

HARVESTING

Blossoms
Look for male, non-fruit producing flowers (female flowers have a swollen mini-squash at the base of the flower and flowers are on shorter stems) and harvest just before use.

Harvest frequently to increase yield; squash seem to get monstrous overnight. While edible at almost any size, seeds are less developed in young fruit, therefore more tender. Using a knife or clippers, cut squash off including some of the stem. By including stem, the fruit is sealed and less likely to mold or dry out.

Summer Squash Comparison

Variety Heirloom/
Hybrid
Plant
Size
Fruit
Size
Fruit
Color
Disease/ Pest Resistance Days to
Maturity
Noteworthy Other Common Names
Squash Summer Baby Round Zucchini HEIRLOOM Seeds ‘Baby Round’ Zucchini Heirloom 2' tall, 3' wide 2"–3½" globe-shape Light green moddled   45 Individual serving; Container friendly Ronde de Nice
Squash Summer Black Beauty Zucchini Organic HEIRLOOM Seeds ‘Black Beauty’ Zucchini Heirloom 2' tall, 3'–4' wide 6"–8" long Dark green   55 AAS winner  
Squash Summer Cocozelle Organic HEIRLOOM Seeds ‘Cocozelle’ Heirloom 2' tall, 3' wide 8"–10" long Dark green moddled with light green stripes   50 Container friendly
Squash Summer Costata Romanesco Organic HEIRLOOM Seeds ‘Costata Romanesco’ Heirloom 2'–4' tall, 3'–4' wide 4"–5" long Dark green moddled with light green stripes   55 Distinct ribbing.  
Squash Summer Early Prolific Straightneck Organic HEIRLOOM Seeds ‘Cube of Butter’ Hybrid 2' tall, 3'–4' wide 6"–8" long Light yellow Tolerant to zucchini mosaic virus, downey mildew and podi virus 50 Container friendly  
Squash Summer Dirani Lebanese Seeds ‘Dirani Lebanese’ Hybrid 2' tall, 3' wide 6"–7" long Greenish-white, speckled   50 Container friendly Koosa
Squash Summer Early Prolific Straightneck Organic HEIRLOOM Seeds 'Early Prolific Straightneck' Heirloom 2' tall, 3'–4' wide 4"–7" long, club-shape Sunny yellow   45 AAS winner, container friendly  
Squash Summer Emerald Delight Zucchini Seeds 'Emerald Delight' Zucchini Hybrid 2' tall, 3'–4' wide 6"–8" long Dark green Powdery mildew, zucchini yellow mosaic virus, and watermelon mosaic virus 2 55 Open growth habit; Container friendly  
Squash Summer Jaune et Verte (Patty Pan) Organic HEIRLOOM Seeds 'Jaune et Verte' (Patty Pan) Heirloom 2' tall, 3'–4' wide 2"–5" scalloped Whitish green turning ivory with green stripes and speckles   55–60 Container friendly  
Squash Summer Max's Gold Zucchini Seeds 'Max's Gold' Zucchini Hybrid 2' tall, 3'–4' wide 6"–8" long Yellow
55 Container friendly  
Squash Summer Scallop (Patty Pan) Blend HEIRLOOM Seeds Scallop (Patty Pan) Blend Heirloom 2' tall, 3'–4' wide 2"–3" scalloped White, yellow, or green (blend)
55 Container friendly  
Squash Summer Sunstripe Seeds Sunstripe Hybrid 2' tall, 3'–4' wide 6"–8" long Yellow with light yellow stripes
50 Plants are spineless, online exclusive  
Squash Summer Tatuma (Calabacita) HEIRLOOM Seeds 'Tatuma' (Calabacita) Hybrid 12' or more 3" oblong Light green, moddled
50 Vine type. Can be harvested as winter squash, somewhat drought and heat tolerant  


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