Protect Your Crops • Basic High & Low Tunnel Components
A Hensley's Seed Co. guide, drawing on advice from Lynn Byczynski, founder of Growing for Market with updatesHigh tunnels, low tunnels, row covers and mulches shield crops from harsh weather and can stretch the season by months, while boosting yields and quality in vegetables, fruits, herbs and flowers.
High Tunnels/Hoophouses
A kit-built high tunnel.
The most powerful protected-growing tool is the high tunnel, or hoophouse: a low-cost, unheated greenhouse set up right in the field. Hoophouses are now standard equipment on many produce and flower farms. One layer of greenhouse plastic over walk-in-height metal or PVC hoops creates a dramatically different growing environment. They don't require power or heat, though some growers add them to push the season further. Usually, though, roll-up sides provide ventilation and the sun supplies the heat.
Common hoophouse crops include lettuce and greens early and late in the year, strawberries in spring, raspberries and tomatoes in summer, and spinach and other cold-hardy vegetables through winter. Depending on your region, plenty of other crops benefit too. Choose crops wisely and a hoophouse can be the most productive ground on the farm.
Tube benders let you build your own high or low tunnels.
There are two main routes to a high tunnel:
- Kits: sturdy, professional-grade structures that are straightforward to put together.
- Hoop benders: a budget-friendly way to build your own. Bend 1 3/8" galvanized chain-link fence top rail (sold at most building supply stores) into hoops and assemble the frame following the bender's plans.
Low Tunnels
A low tunnel over a bed of overwintering onions.
Low tunnels are another protected-growing option: hoops pushed into the ground over a crop bed and covered with spunbonded row cover or greenhouse plastic.
Like high tunnels, low tunnels warm the soil and shelter plants from frost and wind. Use them in early spring for cool-season crops, in late spring to jump-start warm-season crops like tomatoes and peppers, and in fall to keep cool-season vegetables producing longer. They also keep out predictable pests such as flea beetles and cabbage moths.
Low tunnels are cheaper and easier to put up and take down than high tunnels, but give less protection. Hoops bent from EMT (electrical metallic tubing) are much sturdier and last far longer than PVC, so they're more economical over time.
Low tunnel hoop benders are an easy, affordable way to build your own, and come in several widths, such as 3', 4' and 6'.
Hoops + Row Cover
Twine threaded through the loops of looped wire hoopsadds support for the row cover and lets you space hoops farther apart.
Wire hoops and row cover are the fastest, simplest way to cover a crop. Hoop options include:
- Galvanized wire hoops of #10-gauge steel, in widths such as 54" and 76".
- Looped wire hoops, with built-in loops for running twine along the bed to give row cover extra support. Common widths include 16", 26" and 32".
- Make your own hoops from coiled #9 support wire.
Row Cover Uses & Grades
Row cover protects crops while letting water and light through. How much it moderates temperature and how much light passes depends on its weight and material.
Row cover held up by wire hoops.
For Frost Protection
Row cover thrown directly over crops can rescue them from an unexpected frost. Early and late frosts often last just one night, and getting through them can add several weeks of good growing. Most growers keep row cover handy for exactly these emergencies.
Row cover inside a high tunnel adds an extra layer of protection for overwintering crops. For example, a layer of Agribon+ AG-70 over overwintering flowers in a high tunnel provides a big boost in protection.
Double protection: overwintering crops under row cover inside a high tunnel.
Lightweight covers such as DuraSpun™ 55 or Agribon AG-19 work well for general frost protection, and heavier weights are available for overwintering. As you'd expect, heavier covers let through less light; the weights that give the most frost protection transmit the least.
- For row cover weights and their frost protection, see our row cover comparison chart
For Insect Protection
During the season, insect netting over low tunnels or wire hoops keeps out insect pests and birds. The mesh is fine enough to exclude insects while letting enough light, air and rain through for good growth, a useful option for growers aiming to cut back on pesticides.
- Compare insect protection levels in our row cover comparison chart
For Sun Protection
Knitted shade cloth held on hoops with snap clamps. Shade cloth reduces heat stress by cutting the light reaching the crop.
Shade cloth cools crops by reducing sunlight. It's more open than standard row cover, so summer crops get better airflow and water passes through easily. Lay it over looped hoops, low tunnels or high tunnels.
- Check the shade cloth comparison chart to pick the shade level you need.
Securing Row Cover
Hold row cover down with sandbags, 8" x 8" x 8" concrete blocks from the hardware store, hand pegs, or snap clamps. Or bury the edges in soil.
Mulches & Landscape Fabric
Plastic or paper mulches also play a part in protected growing, alone in the field or together with high or low tunnels. Black plastic warms cold soil, while white-on-black keeps soil cooler. Biodegradable and paper mulches don't have to be removed at season's end. All of them block weeds and save labor.
Learn More
For more on protected growing, see The Greenhouse and Hoophouse Grower's Handbook by Andrew Mefferd.
Using some or all of these protected cropping systemshelps take some of the risk out of farming and gardening. For more on growing in hoophouses, see these resources:
Bobcat High Tunnel Kits
- High tunnel kits • comparison chart
- Standard high tunnel kit manual • tech sheet (PDF)
- Pro high tunnel kit manual • tech sheet (PDF)
Stationary High Tunnels
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High Tunnel Hoop Bender (HSC-TUN-013)
Moveable Caterpillar High Tunnel
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Moveable Caterpillar High Tunnel Bender (HSC-TUN-001)
