The best time to grow squash is when the weather is warm. Wait until after the danger of frost has passed in your area to plant both summer and winter squash. Although it's called winter squash, its seeds won't germinate if the soil is cold. While some varieties of summer squash reach maturity in just over a month, most types of winter squash need three months or longer to fully mature.
Check a farmer's almanac or look online to find the date of last frost for your area. Usually, last frost dates are determined by USDA hardiness zones. You can find your zone by looking on a map. Wait until a week or two after the last frost to plant your squash seeds in the ground or to plant seedlings outdoors. You want the least risk for a random cold snap as possible.
Summer squash reaches maturity quickly and typically provides gardeners with more squash than they know what to do with. The plants may be done producing fruit by mid-summer if you plant them in mid-spring. You will still have time, depending on where you live, to plant another crop of summer squash before the frost hits in your area.
To find out if you have time for a second planting, find out the date of the first frost in your area. Count down the days to maturity for the variety of squash you're growing. Go ahead and plant more seeds if there are more days until the first frost than it will take the squash to be ready.
Although the name suggests that it will be cold hardy, you should plant winter squash in the mid-spring to allow plenty of time for the fruit to develop. Unlike summer squash, which should be picked before the seeds grow large, you need to wait for the seeds to fully develop and the outer rind of the winter squash to become hard before you can pick it. If you pick the squash too early, it won't keep on your counter the way a mature squash will.
Give yourself plenty of time to grow winter squash. It can take up to 100 days for the plant to mature and its fruit to be ready. You should aim to be able to pick the squash from the plant by September or October, depending on where you live.
If you live in a cold climate, the summer growing season may be too short for you to successfully grow winter squash if you plant the seeds outdoors. You can try starting the seeds inside, then transplanting them outdoors after the last frost date to extend your growing season. If you're concerned about the short season, calculate the length of time between the last frost and the first frost. For example, your summer may only last 75 days, but you need 100 to successfully grow winter squash. If that is the case, start the seeds indoors at least 25 days before you intend to plant them outside.