Summer Squash

Planting

Summer squash (Cucurbita pepo) is a warm-season crop that grows best at average temperatures between 65 and 75 °F. Squash seeds do not germinate well in cold soil. In the spring, do not plant this crop until after the last chance of frost has passed, and the soil temperature is 60 ºF, 4-inches below the surface.

Summer squash (Cucurbita pepo) is a warm-season crop that grows best at average temperatures between 65 and 75 °F.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Squash plants can be planted from seed or transplants. For more information on growing transplants see fact sheet HGIC 1259, Starting Seeds Indoors. Plant squash in full sun in rows spaced 3 feet apart. Plant the seeds ½ inch deep and 4 to 6 inches apart in the row. When the seedlings are in the one to two true-leaf stage, thin the plants to 12 to 15 inches apart, selecting the most vigorous ones. Squash transplants should be placed 15 inches apart at planting time.

Squash can also be planted in hills. Rows should be spaced 4 to 6 feet apart, with hills 3 to 4 feet apart within the row. Place two or three seeds in each hill.

Squash may be grown on black polyethylene mulch. To plant the squash seed, punch a small hole in the plastic and plant. Black polyethylene mulch warms the soil faster in the spring and conserves soil moisture, which usually will result in an earlier harvest. Other advantages of this type of mulch are weed control and reduction of fruit rot. Install a drip irrigation underneath the black polyethylene mulch to provide a uniform supply of water. Use the black mulch only for the spring crop. If the fall crop is grown on polyethylene mulch, paint the mulch white in order to reflect heat.

For early squash, use a row cover either alone or in combination with black plastic mulch. The row cover can be either clear polyethylene sheeting supported by wire hoops or one of the spun bonded polyester materials that need no support above the developing plants. For example, a light to medium weight spun-bonded polypropylene will provide 4 degrees of frost protection down to 28º F. Remove these materials before the temperatures get above 75 °F as high temperature under the row covers may inhibit the growth of the plant.

Planting Dates

South Carolina Gardening Regions

Piedmont: Abbeville, Anderson, Cherokee, Chester, Chesterfield, Edgefield, Fairfield, Greenville, Greenwood, Kershaw, Lancaster, Laurens, Marlboro, McCormick, Newberry, Oconee, Pickens, Saluda, Spartanburg, Union, and York Counties.

Coastal Plain: Aiken, Allendale, Bamberg, Barnwell, Beaufort, Berkeley, Calhoun, Charleston, Clarendon, Colleton, Darlington, Dillon, Dorchester, Florence, Georgetown, Hampton, Horry, Jasper, Lee, Lexington, Marion, Orangeburg, Richland, Sumter, and Williamsburg Counties.

Zephyr squash is a hybrid between crookneck, delicata, and acorn squash. The fruit has a delicate, nutty flavor.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Recommended Cultivars

Summer squash includes yellow (straight and crookneck), zucchini and scallop. Some varieties have a bush-type of growth instead of the vining habit, which is useful in small gardens.

Cultivars recommended for home gardens in South Carolina are:

• Yellow Straightneck – Early Prolific, Cosmos, Multipik, Saffron, Seneca Prolific, Slick Pik® YS 26, Superpik
• Yellow Crookneck – Destiny II, Dixie, Early Summer, Gentry, Gold Star, Golden Summer, Supersett, Yellow Crookneck, Zephyr Hybrid (a cross between a crookneck, delicata, and acorn squash)
• Zucchini – Black Beauty, Eight Ball, Elite, Embassy, Senator, Spineless Beauty
• Scallop – Early White Bush, Jaune et Verte, Peter Pan, Sunburst

Black Beauty zucchini squash is a popular variety that was introduced in the 1920’s.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Sunburst patty pan squash is scallop shaped and has a good yield.
Millie Davenport, ©2017 HGIC, Clemson Extension

Fertilizing

A soil test is always the best method of determining the fertilization needs of the crop. Information on soil testing is available in HGIC 1652, Soil Testing.

Follow the results of a soil test to maintain a soil pH between 6.0 and 6.5 and optimal fertility levels. If a soil test has not been taken, make a preplant application of 5-10-10 fertilizer at 3 pounds per 100 square feet. Sidedress before the vines start to develop using 34-0-0 at 1 pound per 100 feet of row or calcium nitrate (15.5-0-0) at 2 pounds per 100 feet of row. More frequent sidedressing may be required if the garden is sandy or if leaching rains occur. Do not overfertilize with nitrogen because this encourages excess vine growth and reduces fruit growth.

Watering

Water the garden to provide a uniform moisture supply to the crop. The garden should be watered in the morning so the foliage is dry before dark. Water the garden sufficiently to moisten the soil to a depth of 6 inches. Light watering will encourage shallow rooting of the plants. The critical period for moisture is during fruit set and fruit development.

Squash have separate male and female flowers on the same plant. The female flowers have a swollen portion of stem immediately below the flower that will turn into the developing fruit. Pollinating insects, such as bees and wasps, are necessary to transfer the pollen to the female flower. Poor pollination will result in no fruit formation or either poorly formed fruit.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Cultural Practices

A common problem with summer squash is blossom-end rot. The main symptom is a dark-colored dry rot of the blossom end of the fruit. Blossom-end rot is caused by a lack of calcium in the developing fruit. It may be an indication that calcium is lacking in the soil or that the plant does not have the ability to take up adequate amounts of calcium from the soil. The following measures will help prevent blossom-end rot:

• Test the soil and apply the recommended amount of lime before planting.
• Mulch with 2 to 3 inches of materials such as grass clippings, pine straw and leaves. Mulching prevents rapid soil drying and allows roots to take up available calcium efficiently.
• Do not overfertilize plants with nitrogen or potash. Excessive amounts of these nutrients depress the uptake of calcium.
• Water plants during extended dry periods.
• Add organic matter to the soil. This will help “loosen” clay soils and will improve the water holding capacity of sandy soils. In either soil, organic matter will increase plant uptake of water and calcium.
• Grow squash in raised beds to improve drainage. (Do not grow squash in raised beds in the sandy Central region.)

Squash have separate male and female flowers on the same plant, and pollen must be transferred from the male flowers to the female flowers by bees. Poor pollination can result in improperly shaped fruit. Observe plants closely when blooming begins to determine if bees are present. Use insecticides and fungicides late in the evening to prevent killing bees.

Harvesting & Storage

Summer squash can be harvested about 55 days after planting. For optimum quality, harvest while fruits are tender and still have a shiny or glossy appearance. When growing conditions are favorable, harvest the crop daily or every other day. Harvest crookneck and straightneck varieties when fruit is 1½ to 2 inches in diameter. Harvest zucchini when fruit is 7 to 8 inches long and scallop types when they are 3 to 4 inches in diameter. If desired, all of these squash can be harvested at smaller sizes for extra tenderness. Do not leave large fruit of summer squash on the plant because this will inhibit the development of additional fruit. Store summer squash in a plastic bag in the refrigerator for up to 1 week.

Problems

Insect problems include spotted cucumber beetles, striped cucumber beetles, pickleworms, squash vine borers, aphids, and squash bugs. Aphids are a major problem because they can transmit viruses to the plants. Squash vine borers can cause total collapse of the plant. Plant early because squash vine borers and pickleworms are problems later in the season.

Pickleworm damage occurs when the caterpillars tunnel in flowers, buds, stems, and fruits.
Millie Davenport, @ 2017 HGIC, Clemson Extension

The adult squash bug is a dark gray to dark brown insect that has piercing mouthparts that suck the sap out of leaves.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Squash bug eggs are laid in between leaf veins where they form a V pattern.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Powdery mildew is a common fungal disease on squash leaves.
Barbara H. Smith, ©2017 HGIC, Clemson Extension

Common disease problems include powdery mildew and viruses.

For insect pest and disease control, please see HGIC 2207, Cucumber, Squash, Melon, & other Cucurbit Insect Pests, and HGIC 2206, Cucumber, Squash, Melon, & Other Cucurbit Diseases.

Document last updates were done on 2/23 by Millie Davenport.

Originally published 03/00