How to Grow Cucumbers in an Unheated Greenhouse

Start greenhouse cucumbers just before the last spring frost when temperatures reach 50 degrees F. Greenhouses protect the plants from frost and make earlier plantings possible.

Prepare 5-gallon pots with drainage holes for the cucumbers. Pots allow you to avoid cold or frozen soil, which restricts cucumber growth, and find success with earlier plantings. Designate one pot to each cucumber plant.

Mix a rich, moist and warm potting soil with 1 part peat moss, 1 part organic compost, 1 part perlite and 1 part soil-based potting soil. Don't use soil from the garden, which is cold and damp and may attract pests or weeds. Fill the pots with your soil but leave 1 to 2 inches of space between the lip of the pot and the soil surface. Turn slow-release 5-10-10 fertilizer into the soil for best root establishment.

Plant cucumber seedlings one per pot, with their roots just below the surface. Slide three stakes into each pot, at equal spacing around the sides. Tip these stakes together and tie them at the tip to build a teepee for growing. Train the cucumber to grow up the stakes for better sun and air.

Put the cucumber pots in greenhouse sites with bright, full sun and adequate air movement. Cucumbers won't bloom or bear fruit without full sunlight, even in a greenhouse.

Water the cucumbers with 2 inches of water every four to five days, and check frequently for drying. Cucumbers in pots and inside greenhouses dry more quickly than in-ground cucumbers.

Keep the doors and windows of the greenhouse closed in early spring to protect the cucumber plants. Open the doors and windows for air when nighttime temperatures reach 65 degrees F. Additional air movement encourages better growth and pollination.

Fertilize potted cucumbers with water-soluble 20-20-20 or 15-30-15 fertilizer in mid-season, at their first bloom, and every week thereafter. Water the cucumbers with 1 inch of water, then give them 2 inches of fertilizer mixture for nutrition.