Start small with mini hoop tunnels and cold frames
The following excerpt is from the new book Growing Under Cover: Techniques for a More Productive, Weather-Resistant, Pest-Free Vegetable Garden (Storey Publishing) by Niki Jabbour.
Used with permission.
There is no one right garden structure. If you’re new to gardening, start small and begin with a mini hoop tunnel or a cold frame. This will give you an opportunity to flex your gardening skills and learn techniques like timing off-season growing and how to regulate temperature by venting regularly.
Mini hoop tunnels and cold frames also require little initial investment of either time or money. They can be built using new materials or from old windows, doors, bricks, conduit, and even straw bales. For me, the biggest advantage of these devices is that they are fairly easy to build — especially the mini tunnels — and you see their effectiveness almost immediately. Within a week of sowing seeds in my spring frames, tiny seedlings are popping up. I get to enjoy a full crop of salad greens before my neighbors have even begun to prep their gardens.
Once you’ve had a season or two under your belt, you’ll know if you’re ready to move to a bigger structure like a polytunnel or greenhouse.
Mini Hoop Tunnels
A mini hoop tunnel is exactly what it sounds like: a miniature polytunnel. But unlike a walk-in structure, these pint-size tunnels are quick to build, easy to use, and made with inexpensive materials. There are just two main components: hoops and a cover. The hoops can be made from a variety of materials, including PVC conduit, metal, wire, concrete reinforcement mesh, or even old Hula-Hoops cut in half.
Five Ways to Use a Mini Hoop Tunnel
Frost protection. Top your hoops with a row cover to protect from frost or cold weather. A row cover also shelters crops from heavy rain, hail, or strong winds.
Winter harvesting. We use mini hoop tunnels to harvest cold-season crops all winter long. For winter crops, cover the hoops with a 6 mil greenhouse polyethylene. Twist the ends closed and weigh down the sides to secure them against the winter weather.
Summer shade. I use my mini hoop tunnels from late spring to early autumn to provide some shade from the hot sun. Cool- and cold-season vegetables like salad greens quickly bolt once spring turns to summer. Having a length of shade cloth over the hoops lowers temperatures and prolongs the harvest season. You can also use shade cloth to establish just-planted seeds or seedlings.
Spring, summer, and autumn insect defense. Using a lightweight insect barrier keeps cabbage, kale, broccoli, potatoes, and other pest-prone plants free of insect damage. Float the cover over the hoops as soon as crops are planted and bury the sides to prevent pests from entering the mini tunnel.
Spring, summer, and autumn pest -prevention. Not all pests are small. Deer, rabbits, birds, chickens, and even dogs can eat or damage vegetables. Top the mini hoops with bird netting or chicken wire to keep crops safe.
Types of Mini Hoop Tunnels
In my mind, mini hoop tunnels fall into two categories: lightweight and heavy duty. Your reason for covering the crop and the timing of coverage help determine the type of hoop you’ll need. Are you prewarming spring soil, shading summer-planted seeds from sun, protecting plants from fall frost, or creating a winter harvest tunnel?
Lightweight tunnels. I make lightweight tunnels with wire hoops and use them as spring and fall frost protection in the garden. They do a fine job of protecting crops from cool weather, light frost, heavy rain, and wind, but don’t stand up to snow. I also place them over the beds inside my polytunnel for a double layer of winter protection. For this light work, wire or PVC hoops are fine.
I generally prefer to build my own mini hoop tunnels, as it takes little time and I can match the size to my raised beds, but there are many commercially produced mini hoop tunnel kits you can buy. The kits often have wire hoops and fall into the “lightweight tunnel” category. Depending on the manufacturer, mini hoop tunnel kits may be called polytunnel cloches, mini greenhouses, or mini tunnels. Often the kits are too narrow for my beds, or not long enough.
Heavy-duty tunnels. The other type of mini hoop tunnel is a heavy-duty version made from 10-foot lengths of 1/2-inch diameter PVC or metal conduit. These are strong enough to withstand a snow load and are great for winter protection; if you live in an area that gets a lot of snow, consider adding an extra center support.
Nine-gauge wire. For quick hoops, use 9-gauge wire, which is readily available from a hardware store. You can buy the wire in 50-foot coils and cut it to the desired length with wire cutters. The length of the wire will depend on how wide the bed is and how high you want the hoop to be.
For my 4-foot-wide beds, I cut the wire into 8-foot lengths. This creates hoops that are 3 feet tall before the ends are pushed down into the soil. After that, the hoops are about 2 1/2 feet tall.
For my 3-foot-wide polytunnel beds, I cut the wire into 6-foot lengths and the hoops are 2 feet tall at the center before being inserted into the soil. Once the hoops are installed, they’re about 15 to 18 inches tall. These low hoop tunnels are used for sheltering low-growing greens like arugula, leaf lettuce, and Asian greens.
Flexible 9-gauge wire can also be bent by hand into a square-shaped hoop, so that the tunnel is the same height over the entire bed.
PVC conduit. For over a decade, 1/2-inch-diameter PVC conduit has been the primary material I’ve used for my mini hoop tunnels. Ten-foot lengths are readily available, inexpensive, easy to use, and durable.
To install hoops, pound foot-long rebar stakes into the ground every 3 to 4 feet along each side of the bed, then bend the length of PVC over the bed and slip the ends over the rebar stakes to secure the hoop to the ground. For winter tunnels in areas like mine that have a heavy snow load, a PVC structure needs a center support to add strength. Without it, the tunnels will be susceptible to flattening after a very heavy snow.
Metal conduit. Half-inch-diameter metal conduit makes for a very sturdy hoop to support fabric- or plastic-covered mini hoop tunnels. Metal hoops can be used year after year and are strong enough to withstand snow loads without the center support needed for PVC hoops. To further improve their capacity, I make sure the cover is pulled taut and well secured at the ends, and I knock off heavy snow after a storm. Ten-foot lengths of metal conduit are easy to source at most building supply or hardware stores, and they don’t require a stake to hold them in place; just sink the end of each hoop 6 to 8 inches into the soil, spacing the hoops 3 to 4 feet apart.
The only challenge is figuring out how to bend the metal conduit into hoops! A few years ago, I got a metal bender from Johnny’s Selected Seeds and started bending 10-foot lengths of conduit into super sturdy hoops. This tool has been a game changer. Plus, bending the metal conduit to make the hoops is great fun. It took just a few minutes to get the hang of it and now I can bend a hoop in about a minute.
To make a metal hoop, you first mount the bender to a sturdy structure like a workbench or a picnic table. Then insert a straight length of conduit into the bender and pull the metal tubing down toward you, bending it into the characteristic U-shape.
A metal bender is a great investment for a garden club, urban farm, or community garden where many gardeners can use it to bend strong hoops for season extension.
How High should Your Tunnels Be?
Just-planted seeds or seedlings, or compact crops like leaf lettuce, mâche, or baby greens don’t require a high hoop. But taller edibles like kale, collards, leeks, and Italian parsley can grow several feet high, so take plant size into consideration when deciding on how big a hoop to use.
In general, hoops should be tall enough so that plants aren’t in direct contact with the cover. The exception to this is when lightweight insect barrier fabric is laid on vegetables during the growing season for pest control. Otherwise, plants shouldn’t come in contact with a polyethylene cover or row cover during cold weather as this can cause damage to the foliage. This also holds true in summer when a shade cloth-topped mini hoop tunnel is used to shield vegetables from the hot sun. Keep the cover well above crops to avoid heat buildup around the plants.
Bend Your Own Mini Hoops
My low tunnel hoop bender makes quick work of bending metal conduit for 4-foot wide hoops. The bender needs to be mounted on a sturdy surface like a truck hitch or, in my case, a heavy pallet anchored to a wood base.
- For a 4-foot wide hoop, slide a 10-foot length of half-inch or three-quarter-inch metal EMT conduit through the holding strap, so it extends 16 inches beyond the end of the bender.
- Grab the opposite end of the conduit and bend it toward you until it touches the base of the bender.
- Now slide the tube through the holding straps until it’s centered on the bender.
- Squeeze each end of the tube until they are straight and a U-shape has been achieved. The sides of the tube should be parallel. Once you get going, it will take around a minute to bend each hoop.