How to Grow Acorn Squash

Acorn squash (​Cucurbita pepo​ var. ​turbinata​) is a winter squash, which doesn't mean that you grow it in winter; rather, that you can store it from one to two months into cold weather after a late-summer harvest. Other types of winter squash have much longer storage times that extend well into the winter season. Also unlike other types of winter squash, acorn squash doesn't require a "curing period," so it can be eaten immediately after harvest in summer. The acorn squash is one of a large group of winter squash varieties that includes spaghetti squash, butternut squash, kabocha and many more.

The acorn squash plant is a large vine that can spread out 3 to 12 feet, and it requires considerable garden space. Squash can grow as a vine or a bush, and you typically plant bushy squash on hills for better drainage. A hill for acorn squash should have a diameter of about 24 inches, which is large, but you get a good return for that investment of space because one plant can produce up to five squash, each weighing between 1 and 3 pounds, which is enough to feed several hungry people.

The acorn squash vine produces large green leaves and yellow trumpet-like blossoms that precede production of the fruit, which is dark green with tinges of orange and is shaped like an acorn. The rind of the fruit is hard and inedible, but the yellow-orange flesh inside is full of nutrients, including vitamin C, potassium, magnesium, fiber and a host of anti-oxidants. You have to cook the flesh before eating it, but once you do so and add a little butter and salt, you have a feast on your hands.

Native Americans, who introduced squash to European settlers, have traditionally grown it along with maize (corn) and pole beans, a combination they call the "three sisters." They traditionally plant maize first and then sow the beans when the corn is knee high so they can use the stalks as poles. The role of winter squash in this companion-planting scenario is to keep the ground covered and prevent weeds from growing, and because of its size and large leaves, the acorn squash plant is particularly well-suited for this role.

If you grow the vining type of acorn squash, it's possible to save garden space by training the vine to climb an A-frame trellis and supporting the fruit in mesh bags. The traditional growing method for bush varieties is to build a hill for each plant that encompasses a 50-square-foot area and rises a foot or so above the garden bed to allow water to drain and keep the squash dry. When planting vining varieties, some gardeners locate the hills next to a sturdy structure, such as a fence, on which the vine can climb.

There is plenty of room on a squash hill for companion plants that grow high enough to clear the canopy of the squash leaves. Among the many good candidates (besides beans and corn) are hot peppers, sweet peppers, okra, and onions to name a few, but you should never plant potatoes with squash.

• ​Common Name:​ Acorn squash
• ​Botanical Name:​ ​Cucurbita pepo​ var. ​turbinata​
• ​When to Plant:​ Two weeks after the last frost in spring or 14 weeks before the first frost in fall
• ​USDA Zones:​ Grow as an annual in zones 3-11
• ​Sun Exposure:​ Full sun
• ​Soil Type:​ Rich, well-drained soil with a pH between 5.5 and 6.8
• ​When it's in Trouble:​ Fruit won't form if no bees and other pollinators are around to pollinate the flowers
• ​When it's Thriving:​ Healthy green foliage, showy male and female flowers and well-formed fruit

The roots of acorn squash plants are fragile and don't tolerate transplanting very well, so if you want to get a jump on the season by starting seeds indoors, sow them in biodegradable pots that you can put directly in the ground. Sow the seeds in potting mix on their sides with the narrow edge facing up. The seedlings are cold sensitive, so maintain a constant temperature of at least 60 degrees Fahrenheit in the growing room.

It's more common to sow squash seeds directly in the garden. If you're planting on hills, sow five or six seeds on every hill, putting them 1 inch deep in the soil. When they emerge, thin out all the weaker seedlings, leaving only the strongest one. If you are providing a trellis on which the vine can climb, space the seeds so that each plant has 2 square feet of growing room.

When transplanting seedlings grown indoors, dig a hole large enough to accommodate the entire growing pot and bury it with the base of the seedling stem at ground level. Keep the soil moist constantly while the seedlings are growing. Before you plant, it's a good idea to prepare the soil by mixing in rotted compost to provide nutrients throughout the growing season. It's also a good idea to mulch, which helps keep warmth in the soil and provides a bed for the fruit to prevent it from rotting.

The best zones for growing acorn squash are those that have moderate temperatures and a growing season long enough to allow the fruit to mature, which can take from 70 to 100 days after planting depending on the variety. The root system is not frost tolerant, so all danger of frost must be over before planting outdoors, and the flowers will drop and fruit will fail to form in excessive heat with temperatures exceeding 90 degrees. These conditions are most likely to be met in zones 4 to 7 than in more northerly or southerly regions.

The best time to sow seeds indoors is between two and four weeks before the last frost date. Germination occurs in six to 12 days, which gives the seedlings two to four weeks to grow before moving them outdoors.

When transplanting or direct sowing seeds outdoors, you can do it during the period beginning two weeks after the last spring frost and 14 weeks before the first frost in autumn as long as the soil temperature is above 60 degrees. If you're planting squash with companion plants, you may want to give those plants a chance to grow large enough to avoid being covered by the sprawling squash plant vining along the ground.

The acorn squash plant isn't particular about soil quality, but it will grow best in fertile, well-draining, slightly acidic soil with a pH between 5.5 and 7.0. The addition of compost or manure is always a good idea, and a good way to ensure a proper mixture is to alternate 6-inch layers of soil and compost to a depth of 18 inches. Nourish the plants as needed during the growing season with a balanced fertilizer, such as a 10-10-10 or 12-12-12 mix.

Fruit production will be at its peak if the squash plant is in full sun and gets six to eight hours of direct sunlight a day. Squash needs about an inch of water per week, so you'll have to water the plants if it doesn't rain for seven to 10 days. Always water around the base of the plant and not on the leaves because wet leaves can scorch, and they are more vulnerable to fungal infections.

Acorn squash is always propagated from seeds, which you can purchase online or from a garden center or obtain yourself from a ripe squash in your garden. It's worth noting, however, that hybrid cultivars will not bear true to type from seed (if they germinate at all). Stick with an heirloom acorn squash selection such as the tried-and-true Table Queen.

Because squash has male and female flowers that must be cross-pollinated by bees and other insect pollinators, however, it's possible that some of the seeds you get from your garden have been pollinated with other types of squash, and they may not grow true to form. This shouldn't be a problem, however, if you grow only acorn squash and only one variety in your vegetable garden.

As acorn squash ripens, the rind gets progressively harder, so a good way to test for ripeness is to attempt to poke your fingernail though it. If it goes in easily, the squash isn't ready yet, but if it takes considerable effort to penetrate the rind, the squash is good to go. It can take up to 100 days for squash to ripen, and if a light frost should intervene, that usually isn't a problem because it will just improve the flavor.

Another indication is the color of the rind. The part that touches the ground turns deep orange when the squash is ripe, and a pale-orange coloration means that it needs a few more days on the vine.

As you would expect, a plant with large, juicy leaves growing close to the ground attracts a large number of insect pests that do varying amounts of damage, from chewing holes in the leaves to spreading disease to separating stems. A list of the most common pests has to start with two bugs with "squash" in their names:

• ​Squash bugs​ are shield-shaped black or brown crawling insects with a triangle on the back. They suck juices from the leaves and the stems, causing severe damage at times, and they may also spread a bacterial infection. You can pick these off but look carefully because they often hide on the underside of the leaves.

• ​Squash vine borers​ are large white caterpillars that bore into the stem near the base of the plant and cause the plant to wilt. Look for the entrance holes, which are often littered with frass, and cut into the stem with a clean, sterilized knife at that point and remove the culprit. Exclude this pest by erecting row covers around young plants, removing the covers when the plants are mature and flowering so that pollinators can reach the flowers.

• ​Cucumber beetles​ can be striped or spotted, and it's usually the striped ones that attack squash. They eat the stems and leaves of young plants, which often kills them, and they may also spread disease. You can keep them away with row covers, or you can trap them with sticky traps. If you have a large infestation, suck them up with a wet/dry vacuum.

• ​Aphids, spider mites​ and ​whiteflies​ congregate on the leaves, sucking out juices and leaving deposits that promote mold. It's best to remove these pests by spraying them with water to dislodge them instead of using insecticidal soap, which burn squash leaves.
  

Two of the most important gardening tips to remember are to avoid watering leaves and to always sterilize your gardening tools. If you forget, your squash plants may be affected by any one of a number of fungal, bacterial or viral diseases. Some, like fusarium wilt, live in the soil and are resistant to fungicides and can only be prevented by crop rotation, but others, such as anthracnose, powdery mildew and downy mildew, occur in cool conditions when the leaves are wet, and these can be prevented before a disease takes hold by using fungicides. Applying fungicides after a disease has taken hold generally is ineffective in controlling the problem.

Not all squash diseases are as common, but you should watch for the following:

• ​Mosaic virus​ turns leaves brittle and fragile, stunts plant growth and affects fruit production. It is spread by aphids and cucumber beetles. Remove affected leaves as well as any nearby weeds that are also hosts to the virus.

• ​Bacterial wilt​ is caused by a pathogen that is also spread by cucumber beetles. It spreads rapidly from one or two leaves until the whole plant wilts and dies. This is another good reason to watch for and remove cucumber beetles assiduously and to wash your tools with bleach before using them.

• ​Angular leaf spot​ can leave water-soaked spots on leaves and fruit. It's a water-borne bacterium, and you won't spread it if you refrain from wetting the leaves. Once it occurs, remove infected leaves and stems, clean up the garden and plant the squash in a different place next year.