Hoops for raised garden beds, often called low tunnels or quick hoops, are simple, temporary structures that function as miniature greenhouses over your planting area. These arched frames support a protective covering, creating a modified microclimate around your plants. This structure shields crops from adverse weather, such as frost and harsh winds, and deters common garden pests. Building a low tunnel extends the growing season, allowing gardeners to start planting earlier and continue harvesting later into the fall or winter.
Choosing the Right Materials
Selecting the structural material for the hoops involves balancing cost, durability, and ease of use. The two most common choices are polyvinyl chloride (PVC) piping and electrical metallic tubing (EMT) conduit. PVC pipe is a low-cost, lightweight, and highly flexible option that is easy to cut and bend without specialized tools. However, standard PVC can become brittle and degrade when exposed to ultraviolet (UV) light, often requiring replacement after several seasons.
EMT conduit, a thin-walled metal piping, provides a more durable and sturdier frame that resists damage from strong winds or heavy snow loads. Although EMT is initially more expensive and requires a pipe bender to shape the arches, its longevity makes it a more economical choice. For most raised beds, a diameter of 1/2-inch or 3/4-inch provides sufficient rigidity.
To anchor the hoops, you need components that secure the frame to the ground or the bed itself. The arched pipe ends can be inserted over short pieces of rebar pounded into the soil just outside the bed frame. Alternatively, use specialized tube straps or mounting brackets screwed directly into the wooden sides. Snap-on clips or clamps are necessary for securing the cover material to the pipe frame.
Step-by-Step Construction and Installation
The initial step is accurately measuring the width and length of the raised bed to determine the required hoop length and spacing. The pipe length needed for each hoop depends on the bed’s width, as this dictates the height of the resulting arch. A wider bed requires a longer pipe to achieve a suitable arch height, ensuring plants do not touch the cover.
Once measurements are determined, cut the pipe or conduit to uniform lengths using a PVC cutter or a hacksaw. Hoops should be spaced evenly down the length of the bed, typically every three to five feet, to ensure the cover material is adequately supported. Widely spaced hoops may sag or collapse under the weight of rain or wind.
Installation begins by securely placing the anchors along the long sides. If using rebar, drive 12- to 18-inch sections halfway into the ground just outside the bed frame, leaving the exposed ends ready to receive the pipe. Specialized metal brackets can also be screwed directly to the wooden frame. The cut pipe is then bent into a smooth arch and inserted over the rebar stakes or into the brackets.
To enhance structural integrity, especially for longer beds, add a center ridge pole. This pole, which can be pipe or a wooden furring strip, runs horizontally along the top center of the arches. The ridge pole connects the apex of each hoop, preventing the arches from swaying or collapsing inward. Secure the pole to each hoop using zip ties or pipe clips.
Selecting and Applying Protective Covers
The completed hoop frame can accommodate various materials, each offering different levels of protection and environmental modification.
Clear Plastic Sheeting
Clear plastic sheeting, often six-mil thick, is ideal for maximizing heat retention and creating a greenhouse effect. This is beneficial for significant season extension or overwintering cold-hardy crops. This material traps solar energy and raises the soil temperature, promoting earlier seed germination and transplant growth.
Row Cover Fabric
Lightweight, spun-bonded row cover fabric is permeable, allowing air and water to pass through while providing frost protection. This fabric typically keeps temperatures four to ten degrees warmer than the outside air. It is preferred for protecting crops from mild freezes and drying winds, and it can remain in place during the day without causing excessive heat buildup.
Insect Netting
For pest management, a fine insect netting or mesh is used. This acts as a physical barrier to exclude common insects like cabbage moths and flea beetles.
Proper application of the chosen cover is necessary for the hoop structure to function correctly. The cover material should be cut to allow for at least two feet of excess length on each end and enough width to drape past the edges. The fabric or plastic is pulled taut over the hoops and secured tightly to prevent wind from displacing the cover. Securing methods include using spring clips or clamps along the frame, or placing heavy objects like bricks or sandbags along the bottom edges.