Most varieties of summer squash will be ready to harvest 60 days after planting. They can be harvested when young and tender, or you can wait until they reach their full size, about 6 to 8-inches in length. If you wait too long, they will become less tender and flavorful.Winter squashes take a bit longer, 60 to 100 days after planting. They ready to harvest once the rind of the fruit is hard enough to not puncture with a fingernail.