Growing Squash in Iowa

Summer and winter squash are some of the most popular vegetables in the home garden. Summer squash can be eaten raw in salads, stir-fried, steamed, or cooked in various dishes. Winter squash can be baked, steamed, or boiled.

Types | Suggested Varieties | Planting | Care | Potential Problems | Harvesting & Storing | Squash Blossoms | More Information

Types of Squash

Summer Squash

Summer squashes are large, bushy plants. The fruit of summer squash are harvested when they are immature and have soft skins. Fruit can be stored for 1 to 2 weeks. There are several types of summer squash. These include zucchini (cylindrical, club-shaped fruit), crookneck (long, tapered fruit with curved necks), straightneck (bottle-shaped fruit with straight necks), and scallop (flattened, roundish fruit with scalloped edges).

butternut squash — Butternut Squash. Photo by Cindy Haynes

Winter Squash

Most winter squashes are large, vining plants. (Several semi-bush varieties are available to individuals with small gardens.) Fruit are harvested when they are mature and have hard rinds. Winter squash fruit can be stored in a cool, dry location for 1 to 6 months. Various sizes, shapes, and colors of winter squash are available. These include acorn, buttercup, butternut, and Hubbard.

Suggested Varieties

Summer Squash

Dixie - yellow crookneck
Elite - zucchini
Goldfinger - golden zucchini
Jaguar - zucchini
Seneca Butterbar - yellow straightneck
Spineless Beauty - zucchini
Sunburst - yellow patty pan (scallop)

Winter Squash

Blue Hubbard
Burgess Buttercup
Butternut Supreme
Sweet Mama - buttercup
Table Ace - acorn
Table Queen - acorn
Spaghetti

Planting

developing winter squash on vine — Developing Squash on Vine

Summer and winter squash perform best in fertile, well-drained soils containing high levels of organic matter. They also require full sun. Organic matter levels can be increased by incorporating well-rotted manure or compost into the soil. Prior to planting, apply and incorporate 1 to 2 pounds of all-purpose garden fertilizer, such as 10-10-10, per 100 square feet.

Summer and winter squash are commonly planted in hills. Sow 4 to 5 seeds per hill at a depth of 1 inch in mid-May in central Iowa. Thin to 2 to 3 vigorous, well-spaced plants per hill when seedlings have 1 or 2 true leaves. The last practical planting date for summer squash is July 20. Winter squash must be planted by June 10.

For an early crop, start plants indoors 3 to 4 weeks before the anticipated outdoor planting date. Since squash seedlings don't tolerate root disturbances during transplanting, start seeds in peat pots, peat pellets (Jiffy 7's), or other plantable containers. Sow 3 to 4 seeds per container. Later, remove all but two seedlings. Harden the plants outdoors for a few days in a protected location before planting to lessen transplant stress.

Hills and rows of summer squash should be 3 to 4 feet apart. Hills of winter squash should be spaced 4 to 5 feet apart, with 5 to 7 feet between rows.

Care

Control weeds with frequent, shallow cultivation and hand pulling. Water plants once a week during dry weather. Avoid overhead watering, which can promote powdery mildew in some varieties. Scout frequently for insect pests and address them as soon as they are noticed.

Variety of winter squash — A variety of winter squash in the fall. Photo by Cindy Haynes.

Potential Problems

Squash Bugs

Squash bugs have piercing-sucking mouthparts. Heavy feeding causes entire leaves to wilt, turn brown, and die. Several methods can be used to control squash bugs in the garden. Adults and brick-red egg masses on the undersides of leaves can be removed by hand. Adults can also be trapped under boards or shingles placed under the plants. Turn the objects over daily and collect and destroy the hiding squash bugs. Small, immature squash bugs (nymphs) can be controlled with insecticides, such as carbaryl (Sevin). In fall, remove and destroy plant debris to deprive squash bugs of overwintering sites.

Squash Vine Borer

Squash vine borer larvae bore into squash stems near ground level. Larvae feeding within the vines eventually causes the plants to wilt and die. Squash vine borers can be controlled with insecticides (rotenone, permethrin, or malathion) at regular intervals beginning in mid-June. Apply the insecticide to the base of the vines. After the final harvest, remove and destroy the plant debris. Rototilling in fall or spring may destroy overwintering pupae in the soil.

Poor Fruit Set

For squash fruit to develop fully, bees and other pollinators must transport pollen from the male flowers to the female flowers. If the female flowers aren’t pollinated properly, the fruit will begin to grow and then suddenly shrivel up and die. Bees and other pollinators are less active in rainy weather. Rainy weather could be responsible for poor pollination and rotting of the small fruits. Drier weather conditions should increase pollinator activity.

Blossom-End Rot

Blossom-end rot is a physiological disorder that occurs on tomatoes, peppers, eggplant, and summer squash. On zucchini and other summer squash, the blossom end of the fruit begins to rot and within a short time the entire fruit has rotted. Blossom-end rot is caused by a lack of calcium in the developing fruit. In most cases, there is no need to apply calcium to the soil. Try to maintain an even moisture supply by watering once a week during dry weather. Also, do not over-fertilize plants. Uneven moisture supplies and excessive nitrogen inhibit calcium uptake.

Blossom Drop

Sometimes squash will have a lot of flowers but the blooms seem to fall off early without setting fruit. One reason for this is that they are male flowers. Squash is monoecious with male and female flowers on the same plant. Male flowers are necessary for pollination but will not set fruit. Only the female flowers will develop into fruit. Male and female flowers are similar in appearance. However, the female flowers have small, immature fruits at their base. The first flowers to appear on squash are male. Female flowers appear shortly after that. If the flowers falling off are male, this is normal.

The other reason for blossom drop is poor pollination. Excessively hot or cold temperatures can prevent pollination from occurring. If pollen is not successfully transferred from male flowers to female flowers by pollinators, the female flower will fall off without producing fruit. If the number of bees and other pollinators is low or their populations are suppressed because of insecticide use or unfavorable weather conditions, then successful pollination will not occur. Once favorable conditions for pollination and pollinators return, plants will be more productive.

Zucchini that is too large — Summer squash should be harvested young and small. This zucchini is much too large and will be tough and full of seeds.

Harvesting & Storing

Summer Squash

Harvest long-fruited summer squash varieties when they are about 2 inches in diameter and 6 to 12 inches long. Scalloped types are best when 3 to 5 inches in diameter. Fruit should have soft skins (rinds) that are easy to puncture with a fingernail. Seeds should be soft and edible.

Store fresh summer squash in the refrigerator crisper in plastic storage bags or rigid containers to retain moisture. Stored in this manner, squash will maintain quality for 5-7 days. Summer squash can also be frozen or pickled for longer-term storage.

Winter Squash

Mature winter squash have very hard skins that can't be punctured with the thumbnail. Additionally, mature winter squash have dull-looking surfaces. When harvesting fruit, leave a 1-inch stem on winter squash.

After harvesting, cure winter squash (except for the acorn types) at a temperature of 80 to 85°F and a relative humidity of 80 to 85%. Curing helps to harden the squash skins and heal any cuts and scratches. Do not cure acorn squash. The high temperature and relative humidity during the curing process actually reduce acorn squash's quality and storage life.

After curing, store winter squash in a cool, dry, well-ventilated location. Storage temperatures should be 50 to 55°F. Do not store squash near apples, pears, or other ripening fruit. Ripening fruit release ethylene gas which shortens the storage life of squash.

When properly cured and stored, the storage lives of acorn, butternut, and hubbard squash are approximately 5 to 8 weeks, 2 to 3 months, and 5 to 6 months, respectively.

Squash Blossoms

The flowers of both summer and winter squash are edible. They can be eaten raw or cooked. They are typically cooked by battering and frying or stuffing and frying. Harvest the flowers on the day they open and use them the same day or within a day or two. Clean blooms carefully under cool water as they bruise and tear easily. Most recipes instruct you to remove the stamens from the inside of the flower with scissors or by twisting off the base of the bloom.

Harvest only male flowers. Harvesting female flowers will reduce squash yields. Be sure to leave behind a few male flowers to pollinate the female flowers, but there are often more than enough male flowers to pick and eat. You can distinguish male flowers from female flowers by looking at the base of the bloom. The base of a female flower will have a bulge just below the petals that looks like a tiny version of the squash. This is the ovary that will develop into the fruit. Male flowers will have a thinner stem below the flower and no bulge (ovary) at the base of the petals.