Cucurbita pepo, Cucurbita maxima, and Cucurbita moschata
Despite the easily misunderstood name, winter squash are tender, warm-season annuals in the Cucurbitaceae family, related to cucumbers, melons, and gourds. While winter squash can be grown from fall to spring in some mild-winter areas of California, the name "winter squash" refers not to the growing season but to the potentially long period that squash fruits can be stored fresh (usually at least several weeks and up to several months for some varieties).
The term "winter squash" does not have a simple or clear botanical meaning. At least 5 different species produce fruit varieties that are considered winter squash, including Cucurbita pepo, which also produces the majority of summer-squash varieties. GardenZeus general plant information for winter squash applies to most but not all varieties from the 3 species most commonly grown in California and the United States: Cucurbita pepo (acorn and spaghetti squash, summer squash, zucchini, and many pumpkins); Cucurbita maxima (banana, hubbard, Lakota, turban, and many other varieties); and Cucurbita moschata (butternut squash, cheese squash, and some pumpkins). For a detailed explanation of winter squash species and varieties, see Making Friends with Winter Squash: A GardenZeus Guide to Types, Species, and Characteristics.
Indians introduced squash to Columbus and the West. The ancestors of today's winter squash are believed to have originated in modern Mexico and Central America, with some modern squash species believed native to North America and others to South America. Winter squash remains an important staple food for agrarian and indigenous people around the world, with some varieties producing very large fruits of 40 or more pounds. Nearly all squash grown in modern gardens are descended from species and varieties native to the Americas.
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GardenZeus recommendations in this section are grouped by species for the most commonly grown winter squash in California and the United States: Cucurbita pepo, Cucurbita maxima, and Cucurbita moschata.
Growing your own winter squash allows you to enjoy many interesting, unusual, novelty, and delicious varieties that may be difficult or impossible to find in supermarkets or even farmers markets.
Cucurbita pepo:
For acorn squash, try Table King, a 1974 All-America-Selections winner, among the earliest of winter squash at 80 days, and also performs well in heavy clay soils that are common throughout California. Sweet REBA (for resistant early bush acorn) is a bush acorn variety that produces small fruits to about 2 pounds, a good option if you've had trouble with powdery mildew.
For delicata squash, try Delicata Honeyboat, one of the sweetest of all winter squash varieties, early at 90 days, and good for baking. Sweet Dumpling is an unusual and attractive rounded delicata that produces flavorful small fruits.
Every gardener who enjoys novelty should try Spaghetti Squash at least once for its unusual texture. When cooked, the flesh of mature fruits separates into long strands that can be served like pasta.
Acorn squash
Delicata squash
Spaghetti squash
Many Cucurbita maxima varieties produce large fruits that store for long periods, generally at least 2 months and in some cases up to several months under ideal conditions and if cured properly, but this species also tends to be more prone to insect pests and infestation.
- For a buttercup variety, try the versatile, sweet heirloom Burgess which may stay good for several months when storied ideally under cool, drying conditions.
- For a hubbard variety, try Blue Hubbard, an heirloom that produces 15-to-40-pound fruits on long vines of up to 20 feet. Fruits store for about 4 to 5 months.
- Gold Nugget fruits look like small pumpkins, with better flavor than most pumpkins sold for decoration, on bushy plants. Use them for Halloween decoration then delicious cooking. Gold Nugget is early for maxima at 85 days, and stores for about 2 to 3 months.
- Lakota is an heirloom that produces beautiful, flavorful, green/orange splotched fruits. This variety purportedly was a staple food for the indigenous Lakota people.
- Pink Banana is an heirloom dating back to at least the 19th Century. Its fruits grow up to 2 feet long and are excellent for baking.
- With vines of about 4 to 6 feet and rich orange-red fruits of about 2 to 4 pounds, Red Kuri (heirloom) is recommended for smaller gardens.
- Sweet Meat is a fine-textured, sweet heirloom that produces fruits of up to 15 pounds.
Buttercup squash
Blue Hubbard squash
Gold Nugget squash
Lakota squash
Pink Banana squash
Red Kuri squash
Kabocha squash
Cucurbita moschata varieties are generally more heat-tolerant and often perform better than C. pepo or C. maxima during hot summers. For butternut squash, GardenZeus recommends Waltham, a heat tolerant variety that stores for a few months and that's relatively early for moschata at 100 days. For a cheese squash, try Long Island Cheese, which may also be used as a pumpkin.
Butternut squash
Buying/Selection Tips
Purchase seeds, not seedlings. Squash should generally be seeded directly outdoors. GardenZeus recommends against purchasing squash starts for transplant, especially if rootbound or it has been more than about 2 weeks since germination, as starts may be prone to slow establishment, poor yield, diseases, pests, and other problems.
If you see small flowers on squash starts, do not purchase or plant them. They have already entered their reproductive cycle; this is a condition called "early senescence." If a squash seedling produces flower(s) while at a small size, it may never reach full size and may produce little or no yield.
If buying seedlings, tap the pots, cells, or containers to loosen the root ball and look at roots. Some visible roots, a freckling of white roots at the edges of root ball, or a fine net of roots are acceptable; overgrown, circling, or layered roots at pot edge bottoms are not, and may result in slow-growing, stunted, or unproductive plants. Inspect seedlings before purchasing to be sure that foliage is healthy and free of disease. If you see small flowers on squash seedlings at nurseries, do not purchase them. They have already entered their reproductive cycle; this is a condition called “early senescence.” If a winter squash start produces flower(s) while at a small size, it will never grow to a full-sized plant and may produce little or no yield.
Soil Needs/Tip
Squash are heavy feeders that benefit from well-drained, loose, fertile soil with sufficient calcium and moderate-to-high organic matter. Avoid growing any squash varieties in the same place for more than one season at a time to avoid depleting soil and concentrating pest populations and diseases.
As long as fertility and drainage are sufficient, most squash perform well in a variety of soils. Squash are less fussy than some vegetables about soil acidity, and perform reasonably well in the range of about 5.8 to 6.9 pH.
Squash often grow slowly, produce little yield, become chlorotic, and may be prone to pests and diseases if planted in new, uncultivated, infertile, or compacted soils.
Suitable Microclimate
Squash need full sun and sufficient space in fertile soil that is consistently moist but not wet. They do well in raised beds with southern and western exposures.
Ideal temperature range for germination is 70° to 95°F with fastest germination at the warmer end of this range. Ideal temperature range for growth and fruiting is about 65° to 75°F. Most squash withstand temperatures up to 100°F, but growth and fruiting may be diminished at temperatures above 85°F, and flowers may drop at high temperatures. Most varieties grow slowly or not at all at temperatures below 60°F.
If you've never grown squash, consider starting with zucchini or other summer squash that mature quickly and yield abundantly, often before insect pests and diseases can take much of a toll. Winter squash aren't difficult to grow, but they have high nutrient needs, generally a long growing season, and require more attention than summer squash, such as for curing after harvest. The long growing season required for winter squash means they're more prone than summer squash to succumb to pests, diseases, heat stress, or other garden problems before fruits mature, especially during hot summers.
It's important to pay special attention to growth habit and plant size when planning to grow winter squash. For some varieties, a single squash seed may grow into a behemoth covering 150 square feet or more. Know your varieties; some are comparatively compact, "bush" varieties that may be suited to smaller spaces; while others may become sprawling plants with multiple vines of 20 feet or longer that may overwhelm other plants. Most varieties of winter squash grow vines that spread to several feet or more.
Unlike zucchini and summer squash, which may produce dozens of small fruits that are usually harvested when under a pound in weight, most winter squash produce a few to several fruits. With size of winter-squash fruits often in the 5-to-40-pound range, the total weight of food produced may be greater with winter squash than summer squash.
Because most winter squash store for weeks to several months under ideal conditions, early planting is more important than successive planting as compared to other vegetables. For a small family or household, 1 to 3 plants seeded each at the beginning, middle, and end of your winter-to-spring planting window may produce an abundance of squash for summer through fall and for long-storing varieties, even into the following winter.
Watering Tips
Winter squash benefit from consistent soil moisture and are prone to diseases in wet soils or if overwatered. Seeds may rot if kept overly wet when germinating. Avoid watering with sprinklers. Leaves of squash plants should be kept entirely dry as much as possible.
This butternut squash has willed leaves and needs additional water
Plentiful and consistent moisture is needed from the time plants emerge until fruits begin to fill out. Deep water squash plants, soaking the root zone to at least 4 inches, but leaves and stems should be kept as dry as possible to prevent leaf and fruit diseases. Between watering, allow soil to dry slightly, as squash roots need oxygen as well as water to thrive. For maximum leaf development, which means sweeter fruits, be sure your squashes get at least an inch of water a week.
Plant pre-germinated seeds (not transplants) or seed squash directly outdoors when frost risk is low and daytime temperatures are consistently 65°F and above.
Use raised beds filled with washed sand, local soil, and nutrient-rich compost or amendments rather than planting squash in new, uncultivated, or infertile soils. Squash does not perform well if planted into the compacted clay soils and infertile sandy soils that are common throughout California.
This winter squash being grown on vertical trellis would benefit from additional support
The large, vining types of squash require at least 50 to 100 square feet per hill. Plant seeds 1 inch deep (4 or 5 seeds per hill). Allow 5 to 6 feet between hills. When the young plants are well-established, thin each hill to the best 2 or 3 plants. Allow 7 to 12 feet between rows. Vines can also be grown on a strong trellis, with the squash hanging down. Use fabric slings to support vined squash fruits to maturity.
Winter-squash spacing depends upon variety, planting style, and available garden space. Winter squash is traditionally planted with 2 to 4 seeds per planting hole or mound, then thinned to one plant per hole, spaced about 3 to 4 feet apart for compact and bush varieties; and 5 to 8 feet or more apart for larger vining varieties. Plant seeds about 1 inch deep.
When grown in rows, plant bush varieties about 4 to 6 inches apart in rows 3 to 5 feet apart. Thin plants to one every 2 to 4 feet, depending upon variety. Vining varieties can be seeded about 6 to 12 inches apart, with final spacing of about 5 to 8 feet or more apart in rows that are about 5 to 10 feet apart, depending on variety. Spacing winter squash too closely may result in reduced yield from smaller and/or fewer fruits.
Timelines
3 to 10 days or longer to seed germination. Generally, squash should germinate within a week if kept moist at temperatures of 70° to 95°F.
Transplanting is possible about 10 to 18 days after germination but recommended only for skilled biointensive gardeners and experienced gardeners who are willing to monitor seedlings closely.
10 to 21 days after germination to 1st thinning.
Thin to final spacing by about 3 to 4 weeks after germination, possibly longer during cool weather or for slow-growing plants.
75 to 130 days, sometimes longer, from germination to harvest of winter-squash fruits, depending on variety and growing conditions.
Harvest Period: Most winter-squash varieties produce a-few-to-several fruits that are usually harvested at full maturity, often during a harvest period of days or weeks at the end of the growing season.
Pollination Needs/Tips
Winter squash are monoecious, meaning that a single plant produces both male and female flowers. Pollination is critical for squash to produce fruit.
It is normal for the first few blooms to fall off a squash plant. Early squash flowers are usually all male; no fruits will form from these flowers.
Male and female squash flowers are easily recognized with close observation. Male flowers tend to be on longer stems, and have only a stem at the base of the flower, while female flowers have a tiny immature fruit, which technically is the ovary, between the base of the flower and a shorter stem. Gardeners often assume the wrong gender for squash blooms. As GardenZeus expert Darren Butler has bravely clarified many times over the years, with squash blooms, unlike with humans, the flower with the tube or small sphere is the girl.
Male squash flowers are often produced at a rate of 3 to 4 times the number of female flowers. Don't be concerned if male flowers drop without forming fruits. If established plants drop female flowers and fail to form fruit, lack of pollination is usually the cause.
Male blossom; note there is no fruit growing behind the flower
Like other Cucurbit varieties, male flowers appear first. There are usually three times as many male flowers as female flowers. It is normal for the first few blooms to fall off a squash plant; they are male and will not produce fruit. If flowers continue falling off without forming fruit, or established plants drop female flowers and fruits appear yellow and shriveled, lack of pollination is usually the cause.
If you plan to harvest flowers for cooking and eating, harvest only male flowers. Leave at least one male flower for every 2 to 4 female flowers to allow for pollination.
Bees are primary pollinators for squash in home gardens; if you have a low or nonexistent bee population, you may have minimal yield with squash. Squash blooms alone are not always a strong attraction for bees, but if they're in the area collecting pollen and nectar from other flowers, bees will gladly pollinate squash. Cold or rainy weather may reduce fruiting because pollinators are less active.
If pollinators are still not abundant in your garden, pollinate squash plants by hand. Use a small paintbrush to transfer pollen, or pick male flowers and rub the stamens onto the pistils of female flowers.
Long distances between different squash varieties or isolation is required to save seeds that remain true-to-variety across multiple plant generations. Saving squash seeds in the home garden generally requires tying off female flowers before they open with a stocking, paper bag, or other "hood;" removing coverings once blooms are open to pollinate by hand; then tying off the pollinated blooms again to avoid further pollination by insects. If saving seeds, allow fruits to remain on the vine until they grow to full size and harden. When the stem attached to a mature squash fruit is brown and dead, this usually a means that seeds are ready to harvest.
Interplanting/Companion Planting
Because lack of pollination is a primary reason for poor yield, GardenZeus recommends encouraging bees to visit your squash by planting it near borage, nasturtiums, rosemary, oregano, and other bee-attracting herbs and plants. Allowing vegetables like radishes and carrots to flower and persist in your garden while squash are in bloom may also attract bees and help with squash pollination.
Avoid planting root crops, such as beets, onions, and potatoes, near squash, which may disturb sensitive squash roots when harvested.
The main concern with companion planting for winter squash is that with the vigorous growth, long vines, and sprawling habit of many varieties, squash plants may simply overwhelm, cover, and starve other plants by blocking sunlight. Vining winter squash are generally not recommended for interplanting, but can be successfully grown with tall or large columnar plants, such as sunflowers, amaranth, and corn, especially tall or giant corn varieties.
Squash are heavy feeders. A soil test is recommended to determine nutrient levels prior to applying fertilizer.
Work compost, composted manures, or well-rotted organic matter into soils before planting, and maintain nutrient-rich surface dressings under mulch. Bury plugs of finished compost or worm compost a few inches outside of the driplines of established squash plants 2 or 3 times per growing season and water thoroughly. For soils low in calcium, crush or grind up eggshells and add to the soil surface under mulch at the base of each plant. Grow squash or other cucurbits only once every 2 to 4 years in a given bed or garden area to allow the soil to recover between plantings.
GardenZeus recommends adding nitrogen in the form of diluted urea or a cup of chicken manure diluted in 4 gallons of water (half cup if fresh manure) and mixed thoroughly, after seedlings are a few to several inches tall and about once or twice per month thereafter. Adding too much nitrogen may result in rapid growth and lush, high-carbohydrate leaves that attract insect infestation; and slowed or reduced yields.
In hot-summer areas, reduce or discontinue fertilizing with nitrogen by late spring or early summer to avoid producing large, lush leaves that will tend to wilt and cause stress to squash plants during summer heat.
Fish emulsion or seaweed extracts applied as drenches or foliar spray may be beneficial in soils that are infertile, alkaline, or lacking micronutrients.
Mulching
Mulching squash plants is particularly important, especially during warm-to-hot weather, to maintain even soil moisture, cool soils during hot weather, and inhibit weeds to avoid root disturbance to squash from weeding. Use a half-inch of fine mulch for small starts under 4 inches in height; increase to 1 to 2 inches or more of fine to medium mulch after plants are 6 to 12 inches tall.
Straw and/or pine needles make good mulches for squash. Having plenty of mulch around squash is a benefit when plants begin fruiting; mulch can be mounded here and there as necessary to support squash fruits and prevent them from resting on damp soil, which encourages prematurely rotted fruit.
Pruning/Cutting Back/Pinching/Separating
Winter-squash plants may be pruned and/or flowers and fruits thinned for many specific reasons, including improving size and quality for large fruits, or for intensive growing such as in a greenhouse, small growing space, or container. For most gardeners growing squash outdoors, there is no need to prune plants, and doing so may encourage pests or diseases and reduce yield.
Pinch off or remove early flowers from young squash plants to encourage vegetative growth, for a more vigorous and larger plant before it begins putting energy into fruiting, which may increase overall yield.
Remove all flowers and small fruits that appear late in the growing season to optimize size and quality of existing winter-squash fruits before harvest.
If you are trying to grow large fruits or a single giant winter squash for some varieties, remove all new flowers and all smaller fruits after selecting the primary fruit(s) that will be grown to maturity.
GardenZeus generally does not recommend cutting back or removing squash leaves or stems. One exception is judicious thinning of leaves if plants wilt persistently during hot weather despite having ample soil water.
From seed. GardenZeus recommends open-pollinated, untreated, organically grown seeds.
Container Gardening
Because of plant size and needs for soil volume, winter squash is not an ideal container vegetable. It does well in raised beds or very large containers. Many varieties of winter squash need containers of trash-can size or larger filled with fertile, living soil to produce good yields. A trellis or structure for climbing may help vining winter-squash varieties to remain manageable, receive enough sunlight, and yield well when grown in a container.
Bush, semi-vining, and smaller varieties of winter squash may produce good yields in well-drained containers that are at least 16 to 18 inches wide and deep.
Table King is an early acorn squash, a 1974 AAS winner with 4-foot vines that is suited to growing in containers. For delicata types in containers, try Sweet Dumpling or Delicata Honeyboat. Red Kuri is a compact variety that produces smaller fruits of about 2 to 4 pounds. Burgess Buttercup produces fruits that store for several months on vines to about 6 feet. Gold Nugget produces delicious squash that look like small pumpkins on bush plants. For more details about these varietes, see "Recommended Varieties/Cultivars" in the GardenZeus section "Getting Started."
Plant 2 to 3 squash seeds per large container and thin to 1 plant when seedlings are 2 to 4 inches tall. Soil tends to dry out more frequently in containers or raised beds, so be sure to monitor as needed and provide sufficient and consistent water.
Winter squash is a warm-season crop because it is frost sensitive, but also suffers in heat. It grows and fruits best at temperatures from 60° to 85°F, with optimal growing temperature between 65° and 75°F.
Seed squash or plant pre-germinated seeds directly outdoors in late winter or spring when frost risk is low and daytime temperatures are consistently 65°F and above. Planting early is important in many California areas to allow for the long growing season required for most winter-squash varieties before hot weather stresses plants and reduces yields. Starting seedlings early, while temperatures are still cool to cold, increases risk of damage or loss of plants to frost during cold years and in colder areas of California, but also generally minimizes problems from insect pests, which can be so intense during warmer weather that it can be difficult to establish seedlings.
Use row covers, or improvised materials such as cloth sheets or cardboard, overnight to protect plants from late frosts. Remove covers during the day for sunlight and to allow pollination by insects.
Winter squash may also be grown in mild-winter California areas beginning late summer or fall. This is a less-certain planting window than late winter or spring, as young seedlings may become stressed or die quickly in dry soils during late heatwaves, and plants may need protection from occasional late-fall or winter frosts. Plants may grow and produce slowly or not at all during cool-to-cold weather. Plant pre-germinated seeds or seed directly outdoors during cool periods beginning late summer or fall.
As winter squash plants mature, they may be infested by leafminers and other insects. Leaves may be covered in mildew, chlorotic, or bug-eaten. Plants often continue to produce mature fruits and produce a yield despite looking ragged and unhealthy.
At the end of the season, remove and discard all squash plants. Compost any that are free of disease, but dispose of vines infested with powdery mildew in the city green waste bin.
How to Harvest
Winter squash are often left unharvested until the end of a long growing season when plants have died back. Different varieties may have unique clues or signs that fruits are mature. Most varieties are ready for harvest when fruits are in full color, rinds are firm, and the nearby vines and stem to a fruit have shriveled or died. Plant leaves and stems may generally be turning brown and dying.
Many varieties are ready for harvest when the rind has become so hard that it can't be easily nicked or dented with a fingernail. Acorn squash and other shorter-season Cucurbita pepo varieties are often ready for harvest when rinds are still somewhat soft.
Acorn squash varieties are usually mature when their skin is dark-green, the part of the fruit that was touching the ground shifts in color from yellow to orange, and/or the stem to the fruit has shriveled and dried.
Be patient and wait until full maturity to harvest winter squash. Fruits will not continue to mature or harden if harvested early, and immature fruits will not last well in storage.
Use a knife or pruning shears to cut squash from the vine. Loppers or a pruning saw may be needed for large fruits or thick stems. Leave 2 to 6 inches of stem above the fruit, and avoid using the stem stub as a handle for lifting or moving a squash fruit. A sufficient stem stub slows and reduces microbial infection coming in through the stem and will result in a longer storage period for the squash.
Most varieties of winter squash are cured after harvesting (not acorn and delicata types, for which curing can degrade the quality of the fruit). Curing reduces water in squash fruits and hardens their skins, preparing them to last as long as possible in storage. Curing also tends to increase sweetness of winter squash because it reduces their water content in proportion to sugars. Winter squash fruits are ideally cured unwashed outdoors in sunlight at warm temperatures (ideally about 80° to 85°F) for about 7 to 14 days. Fruits should be kept dry while curing, and may need part shade to avoid sunscald, particularly during warm-to-hot weather. They can be cured indoors in a well-ventilated area if weather is cool or rainy, or if curing fruits may be subject to wet soil, sprinklers, or other irrigation.
Harvesting Tips
Winter squash blossoms are not usually harvested or eaten because they tend to be more bitter than summer squash blossoms.
Winter squash resting directly on soil may be prone to rot. Mound mulch under squash fruits or elevate them on a dry surface such as a wooden board, especially from the time they begin to color until maturity.
Length of growing season varies widely among varieties of winter squash. The "days to maturity" from seed packets gives a basic guideline but is not always accurate due to variations in weather and growing conditions.
Attentive gardeners may improve their winter-squash harvest by removing blooms and new fruits that appear late in the growing season, and which may not reach maturity before the plant is exhausted. This will help to encourage growth and quality of existing fruits.
Most winter squash varieties can be picked early and eaten like summer squash but won't be as sweet or flavorful as after full maturity and curing. Butternut squash in particular is popular for harvest and eating while immature.
Curing and a few weeks of storage improves flavor of many varieties including Buttercup, Butternut, Hubbard, and Kabocha. See "How to Harvest," above, for curing instructions.
