One of the major objectives for greenhouse production is controlling the temperature inside. Greenhouse plants thrive when the temperatures remain within a certain range. Venting heat away from a greenhouse is as simple as opening doors or rolling up the walls. But creating heat in a greenhouse takes more imagination. Large, commercial greenhouses use expensive heaters or radiators. You can heat a small hoop-style greenhouse with a material as simple as compost, bubble wrap insulation or water in rain barrels.
Dig a series of trenches that are 3 feet long by 3 feet wide through your hoop house.
Fill the trenches with 1 part manure and 2 parts sawdust to create compost.
Water your compost mixture with a garden hose. Keep your compost as wet as a wrung-out sponge.
Check your compost with a meat thermometer every few days. If the compost temperature drops below 120 degrees, turn the compost inside out with a shovel.
Cover trenches with a sheet of ¾-inch plywood to create walking paths over them.
Cover the exterior of your greenhouse with polyethylene bubble wrap for a light, removable insulation. Leave bubble wrap on during daylight hours to create additional heat inside a hoop house when you expect the weather to worsen. Use bubble wrap to create smaller heating tents inside your greenhouse for tender plants.
Cover plants with floating row covers at night to protect them from changes in temperature.
Cover plants with upturned mason jars or bell-shaped glass jars known as cloches to create mini-greenhouses within your hoop house.
Increased Thermal Mass
Purchase opaque black rain barrels or reconditioned steel drums from a garden center or hardware store.
Fill the barrels with water.
Place the rain barrels at central points around your hoop house where they will absorb the maximum amount of sunlight. Use them as legs for potting benches or seedling tables. Rain barrels will absorb solar energy throughout the day and radiate it back at night.