Direct seed Black Zucchini Summer Squash ½ inch deep into hills or rows with four to five seeds per hill. Summer squash like warm soil and are very sensitive to frost, so plan accordingly. Unlike sprawling winter squash, summer squash grows on compact vines. This variety of squash is picked when zucchini is between six to eight inches in length. Pick your vines regularly and grow a virtually unlimited supply of Black Zucchini Summer Squash throughout the season long!