Winter squash might sound a bit misleading, since this veggie, like its summer squash cousins, hates the winter and withers at the thought of frost. The name actually refers to its long growing season, which tells us that squashes won’t be harvested til near winter, even if plants are started in early spring. Winter squash grows in the form of a vine, reaching up to 15 feet in length, so make sure your garden space is adequate for these sprawling, large-leaved plants, or use a trellis to encourage vertical growth.
A rare open-pollinated Kabocha squash, Blue Kuri (or Blue Hokkaido) squash is a great choice for gardeners interested in seed saving. Fruits will grow to 2–3 lbs each—occasionally reaching up to 8 lbs—with a bluish-grey skin and sweet, thick, rich-tasting yellow-orange flesh. Great for storing through the spring, its thick skin is also edible. Overall very easy to grow; however, this color of squash is often irresistible to squash bugs. With some vigilance and under-leaf patrolling, you should be able to get several tasty squashes from this spreading vine.
Seed Depth: 1/2–1″
Space Between Plants: 18–24″
Space Between Rows: 3–5′
Germination Soil Temperature: 70°F
Days for Germination: 7–10
Sow Indoors: 2–4 weeks before average last frost date.
Sow Outdoors: 2–4 weeks after last frost when soils have warmed.
Vegetative: Can be propagated by taking stem cuttings. Cuttings should contain between 1–3 nodes. Root your cuttings in well-drained soilless media. Plants grown from cuttings will potentially produce fruit earlier than plants grown from seed. Additionally, burying several nodes along the stem of an established plant will encourage it to send out new roots from those points. This is a good insurance plan for your plant, since it can continue to grow if one section of stem is damaged.
Despite the name, winter squash grows best in warm seasons, preferring temperatures around 70–80°F. Winter squash do not tolerate frosts, so ensure that there is enough time for the fruit to mature before your overnight temperatures dip below freezing.
Natural: Full sun.
Artificial: Will grow well under artificial lighting. Needs at least 6 hours of light daily; however, more is preferred.
Soil: Prefers well-drained sandy, loamy, or clay soils. A pH between 5.5 and 6.5 will keep plants healthy and nourished.
Soilless: Start seeds in soilless mixes and rockwool cubes.
Hydroponics: Thrives in hydroponic systems including media beds filled with pine bark. Nutrient solution pH should be kept between 6.0 and 6.5.
Aeroponics: Thrives in aeroponic systems.
Water: Requires moderate to high levels of water. Seedlings must be kept moist, but take care not to overwater. Maturing plants need regular water and grow best in consistently moist soils. If your plant looks wilted early in the morning, it’s a good idea to water deeply as soon as possible. Wilting during the hottest parts of the day is normal. As fruits near maturity, you should reduce watering to prevent rot.
Nutrients: Requires high levels of nutrients. Plants will benefit from regular feeding every 2–3 weeks during the growing season. Avoid high nitrogen fertilizers because soil that is too rich in nitrogen will result in excessive foliage production. Sidedress with compost tea 1–2 times per month. Applications of alfalfa meal, feather meal, ground oyster or eggshells, green sand, and kelp meal can be useful in providing trace minerals.
Foliar: Foliar sprays of manganese, boron, and magnesium will provide these essential nutrients to plants grown in poorer soils. Compost tea can also be applied as a foliar spray.
Mulching: Use mulch to moderate soil temperature and conserve soil moisture in dry or hot climates.
Support: Use a trellis to keep vines off the ground and save space. You’ll need to train the plant up the trellis yourself, weaving vines through the openings or using a loose loop of twine to tie them of. When the fruits begin to form, you can use old cut-up pantyhose to make a sling for them and keep their weight supported!
Deficiency(s): A calcium deficiency can cause blossom end rot.
Rotation: A 3-year rotation away from all plants in the cucurbit family is recommended if you have disease or pest issues.
Companions: Grows well with the Three Sisters, peas, nasturtium, radish, mint, onion, marigold, and oregano. Avoid potatoes.
Harvest: Cut fruits from the stem at least 1″ from their tops before the first heavy frost of the season or when fruits have developed tough skin and vines are beginning to die back. Handle fruits very gently. Light frosts will kill foliage and usually not damage the mature fruits, so you can usually wait until after the first light frost to make finding and harvesting of fruits easier in a large plot.
Storage: Store in a cool, dark, dry place for later use. Only mature and cured fruits will store well. Curing can be done in the field, allowing cut fruits to dry in the sun, covering them overnight if temperatures drop below freezing. To cure indoors, store in a dry, well-ventilated and warm (80°F) area for 3–5 days. Once cured, winter squash will keep for several months at 50–60°F in an area with low humidity and good ventilation. To further extend shelf life, you can try buffing the outer skin with a light vegetable oil. First wash the fruit, then dry thoroughly. Rub the oil onto the surface, then buff off until there is only a light shine and no greasy feel.
Seed Saving: As with other cucurbits, you can be sure of saving generically pure seeds with this variety only if there’s a 1/2 mile radius where the only C. maxima being grown is the Blue Kuri Kabocha. If that’s the case, you’ll need to allow fruits to mature on about 10–20 plants. Wait until a month from harvesting the fruits, then scrape out the seeds, wash away any goop and fibers, and dry the seeds on a screen. Once fully dry, store saved seed in a dark, cool location for best results.
Preserve: A cooked puree of winter squash will freeze well. Canning should be done only by experienced canners, since winter squash’s density makes it hard to heat evenly, posing a safety risk. If canning, you must use a pressure canner. Cut into 1″ cubes and blanch for a few minutes. Pack jars with the squash, a splash of lemon juice, and fill each jar to within a half inch of the top with the leftover blanching liquid. A safer way to preserve is by dehydration. Blanch thin strips, then dehydrate in an oven on low or use a dehydrator. Before use, allow them to rehydrate in a bowl of hot water. You can also pickle or brine winter squash for a tasty treat.
Prepare: Usually roasted, baked, or pureed into soups. Use similarly to pumpkin. To prepare, first remove the stem, if present. Cut the squash in half from top to bottom and scoop out the seeds. Seeds can be rinsed, dried, and roasted with oil and salt for a tasty and healthy snack. You can bake the flesh of the squash with the skin on or off, in cubes, wedges, or entire halves. The edible flowers are usually eaten battered and fried.
Nutritional: This fleshy fruit is low in calories and a good source of dietary fiber. Provides vitamin(s) A, C, B, potassium, manganese, copper, and omega-3 fatty acids. The yellow-orange flesh is given its color by high levels of beta carotene.
Medicinal: The amino acid cucurbitin, found in the seeds of plants in the cucurbit family, can be used in the treatment of parasitic worms, including Schistosomiasis. Winter squash is also sometimes used in cosmetics for the treatment of dry and sensitive skin. The high levels of carotenoids and vitamin A found in the fruits are beneficial for eye health and visual acuity.
When the winter has got you feeling blue, grab a Blue Kuri Kabocha from your pantry and make a batch of this Kabocha Squash Fennel Ginger Soup with Spicy Coconut Cream.
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