Things You'll Need
2-gallon nursery containers
30 percent shade cloth
The warm, moist greenhouse environment provides several benefits when growing squash, particularly summer squash varieties such as zucchini and crookneck. Since squash seeds require temperatures above 65 degrees F to germinate, greenhouses allow earlier sowing and an earlier yield, providing a longer growing season for gardeners in cold northern climates. Greenhouse growing also provides the intense light, warmth and constant moisture squash plants need to bear a large crop of fruit. It is a simple and highly effective way of growing squash – but provide the plants with enough space to spread out and good air circulation to keep them healthy.
Combine three parts potting soil, three parts compost, one part medium-grit sand and one part perlite to create a nutrient-rich and moisture-retaining growing mix for the squash. Mix the components together by hand until the medium is fairly uniform in appearance.
Fill a 2-gallon nursery container for each squash plant using the growing mix . Leave 1 inch of space between the top of the pot and the surface of the soil. Saturate the soil with water and let the moisture run off for 10 or 15 minutes.
Sow two squash seeds 1 inch deep in each pot of soil. Sprinkle medium-grit horticultural sand across the top of the seeds to hold them in place and provide a measure of insulation against drying out.
Place the nursery containers against the southern wall of the greenhouse where they will receive the most sunlight. Space the containers at least 4 feet apart to provide plenty of space for the vines to spread.
Secure 30 percent shade cloth above the containers to diffuse the sunlight and keep the squash seedlings from scorching. Hang the shade cloth along the ceiling panels and halfway down the side of the southerly windows.
Mist the soil lightly each day using a spray bottle or a garden hose with a mist nozzle. Moisten the soil just until a small quantity of water collects on the surface and the soil is wet to a depth of 1/2 inch.
Watch for squash sprouts in five to eight days. Remove one of the two squash seedlings from each pot once they produce a mature set of leaves and stand at least 2 inches tall. Remove the smaller of the two.
Vent the greenhouse for two hours each day to improve air flow and lessen the likelihood of mold growing in the nursery containers. Open the greenhouse on very hot days when daytime temperatures exceed 95 degrees F.
Pollinate the squash blossoms by hand since pollinating insects generally are not present during greenhouse cultivation. Identify the female blossoms by looking for those with a large swelling at the base, which is the ovary, and a knobby yellow protrusion inside at the base of the petals, which is the stigma. Identify the male blossoms by looking for those with large, well-developed petals and pollen-covered protrusions inside called anthers.
Pluck the male blossom once it fully opens to reveal the anthers. Peel off the petals until the anthers are exposed completely. Touch the anthers to the stigma inside the female flower to impart the pollen. Repeat this with each female flower until all are pollinated.
Watch for the development of fruit in five to seven days. Harvest the fruits once they develop mature coloring and the flowering tips have shriveled and fallen off.