Summer squash (Cucurbita pepo) is a warm-season vegetable that grows well in the warm springtime soils of South Carolina. The planting time and cultivation practices you'll use will depend on what part of South Carolina you live in--whether it's the piedmont, central or coastal region--because the soil quality and average temperatures vary slightly between these regions. Summer squash has a short growing time of less than two months between seed planting and harvest, making it possible to plant both a spring and fall crop in South Carolina.
Select a planting site for your summer squash that's in full sunlight and has rich, well-draining soil. Prepare the soil at the planting site by removing all grasses, weeds or debris and loosening the soil to a depth of about 4 to 6 inches. Mix into the soil 3 pounds of 5-10-10 NPK fertilizer per 100 square feet.
Plant your summer squash seeds directly into the ground in spring, after all chance of frost has passed and the soil has warmed to at least 60 degrees F. The ideal planting time is between April 15 and May 15 for the piedmont region of South Carolina, April 1 to April 20 for the central region or March 20 to April 10 for the coastal region.
Plant the summer squash seeds 1/2-inch deep into the soil, spaced 4 to 6 inches apart in rows that are 3 feet apart. You can also plant the squash seeds in hills raised about 3 inches above ground level, with two or three seeds in each hill. Space the hills about 3 to 4 feet apart in rows that are 4 to 6 feet apart.
Water your summer squash deeply once every two or three days in the absence of rainfall to keep the soil evenly moistened. Moisten the top 6 inches of soil around the squash plants, watering in the morning. Don't allow the soil to dry out, especially when the summer squash fruits are setting and developing.
Feed your summer squash plants 1 pound of ammonium nitrate or 2 pounds of calcium nitrate per 100 feet of row before the vines begin to develop. Apply the fertilizer as a side-dressing, spreading the granules evenly beside the rows.
Harvest your summer squash by picking the fruits from the vines when they're tender and still look glossy or shiny, usually beginning about 55 days after planting the seeds. Harvest the zucchini types when they're 7 to 8 inches long, the crookneck and straightneck types when they're 1 1/2 to 2 inches wide and the scallop types when they're 3 to 4 inches wide.