Heather N. Kolich, ANR Agent, UGA Extension Forsyth County
Floating row covers and low hoop houses can extend the gardening season later into the fall and can help gardeners get a head start on early spring plantings. They work by capturing ground heat and keeping it around the plants under the covering. These temporary structures can increase the temperature inside the hoop house by up to 8 degrees, simply by preventing ground heat from escaping into the air. Heavier frost blankets can help with early spring germination of seeds. Low hoop houses also offer protection from pest insects and small critters.
Row covers are lightweight fabric made from polyethylene, spunbonded polyester, or spunbonded polypropylene. They are non-woven fabric similar to interfacing used in sewing. The porous fabric allows sun, rain, and air to filter through to the plants inside the tunnel. Hoops are used to lift the fabric away from plants to allow for growth and prevent plant injuries that can occur if the fabric rubs against them.
For frost protection, it’s important that the fabric reaches all the way to the ground on all sides of the planting bed. This traps ground heat inside the tunnel. Capturing that heat can raise the temperature inside the tunnel by 2-8 degrees Fahrenheit above the outside air temperature and provide frost protection for a few to several degrees below freezing, depending on the fabric density. Frost protection increases with fabric thickness, but light penetration decreases. A bit of shade can benefit some plants, but too much shade can cause poor growth. While most seeds don’t require sunlight to germinate, lettuce seeds do.
Select the appropriate product for your planting season and needs. The weight, thickness, or density of the fabric, percent of light transmission, and temperature of frost protection should be provided on the labeling.
Low hoop houses can provide some wind protection, but the covering can be blown astray in heavy winds. Use lumber, bricks, sandbags, or smooth rocks to hold the fabric firmly to the ground. Garden staples can tear the fabric. With care, the row cover can last for several seasons.
Using plastic to cover a low hoop house can increase heat capture, but plastic presents other problems. It blocks rain and air from flowing to the plants. The plastic must also be pulled back daily to provide ventilation and release excess heat.
In North Georgia, we usually see our first fall frost around October 30 and our last spring frost around or after April 15. Fabric coverings can stay over plants in the fall, but the fabric should be raised above the growing points. Most of our fall-grown plants are leafy greens or root crops that don’t need an insect pollinator to produce the parts we eat. Enclosing these crops within a hoop house at planting helps keep pest insects like cabbage loopers off the plants. Well-anchored fabric can also deter small mammals. The fabric covering must be removed from spring plants before they mature to allow for growth and pollination.
Now that low hoop tunnels have gained in popularity, kits are available to order. However, DIY’ers can construct a simple and economical low hoop house with flexible ½ inch PVC pipe. For raised beds, simply bend the PVC pipe and push the ends into the soil inside the frame. Heavier PVC pipe can be used to construct a framework to hold the hoops in place over in-ground rows of plants. If the row covering is attached to the lower framework, the whole structure can be rolled or lifted aside to allow access to the plants for harvest and care.
Materials needed for low hoop house construction:
- 1/2 inch PVC pipe – rigid but flexible
- PVC pipe cutter (if needed)
- Floating row cover or Ag fabric
- Anchoring items, such as lumber, bricks, sand bags