Make an Easy, Inexpensive Mini-Greenhouse With Low Tunnels

Learn how to make an easy, affordable mini-greenhouse using row covers and low tunnels for season extension and natural pest control.

| February/March 2013

During any time of year, a visitor to my Zone 6 garden will find at least a couple of low tunnels at work. Supported by wire hoops or arches made from wire fencing, my garden tunnels are covered with row cover and/or plastic when it’s cold to create mini-greenhouses. During winter, they provide protection from wind, hail, and most critters while speeding soil warm-up for summer crops. In summer, I cover the greenhouse tunnels with lightweight row cover or tulle to exclude insect pests such as flea beetles and squash vine borers, and to provide shade for heat-sensitive crops such as lettuce. The cycle begins again when I plant fall-sown onions, such as ‘Olympic’ and ‘Top Keeper,’ or hardy greens inside my multipurpose, portable mini-greenhouses.

Anatomy of a Low Tunnel

Any garden tunnel has three parts — the support hoops or arches, the cover, and the pins, ropes or weights to keep the edges secure. For supports, many gardeners use hoops made from stiff, 9- or 10-gauge wire, or they make their own hoops from inexpensive half- to 1-inch diameter poly pipe (the type used for underground water lines). Pipe hoops are more likely to stay erect if they are slipped over sturdy rebar stakes, or into sleeves made from rigid metal or PVC pipe. They can also be attached to the outside of framed garden beds with metal brackets (visitthe Image Gallery for examples). Tunnels made using fence-wire arches will be more secure if staked down with U-shaped metal pins.

Whether made from wire, plastic pipe or another smooth, non-snagging material, your hoops should be the right length to arch over your garden beds. For 3-foot-wide beds, hoops cut 76 to 80 inches long are best. Hoops are usually spaced 2 to 3 feet apart, so you may need a lot of them. The cheapest way to go is to buy a spool of 9- or 10-gauge wire or poly pipe and cut the hoops yourself. If that doesn’t seem doable, consider hoops available online. Expect to pay $25 for 20, or more for double-wide Super Hoops ($15 for six).

I have used a set of wire hoops for 10 years and will probably use them for 10 years more. In some instances, however, arches made from wire fencing work better than hoops. The main advantage of fencing arches in winter is their ability to withstand heavy loads of ice or snow without collapsing (as hoop-held tunnels are prone to do).

Several seasons back, I received a letter from a reader in Washington, D.C., who was harvesting 6-inch-wide spinach leaves in February under a snow- and ice-covered tunnel supported by an arch of wire fencing covered with plastic, and I’ve been using fencing arches ever since. In spring, I can plant compact varieties of peas under an arch-supported mini-greenhouse, and then take off the cover and let the peas use the arch as a trellis after the weather warms. Later, I do the same thing with pickling cucumbers — first using row cover over a fencing arch to exclude insect pests, and then removing the cover to let in pollinators and allow the cukes to ramble up through the arch that’s now doubling as a trellis.

Two types of fencing dominate my collection of arches — woven-wire fencing with big, 6-inch openings, and stiff welded wire with 2-by-4-inch openings. I use the more flexible woven wire in situations when I know I’ll want to uncover the tunnel and reach in often — to weed carrots or onions, or to harvest leafy greens, for example. I choose the arches made from the smaller fencing if I need to protect newly planted beds from animals or birds. Also, you can staple the plastic to the arch and then the unit is very easy to take on and off as needed. Another option is to construct a rigid, portable mini-greenhouse by connecting electrical conduit pipe to a rectangular foundation frame, as shown in the Image Gallery. This greenhouse tunnel is light and rigid enough to pick up and move.

1/27/2013 5:27:15 AM

Carol Parrish Does anyone make a fine netting to use instead of a light roll cover?. I am planning on making a low tunnel and would rather not use the light roll cover since I did not have good results the last time. My plants did not grow as well as expected and the fabric tore easily .

Jon Streufert
1/26/2013 4:28:47 PM

Just curious what specific types/brands/dimensions of plastic covers you have used, where you get them, and how long they last. I already use hoop houses, but your ideas on wire fencing for easy removal is a good one. Thanks.

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