As you look into extending out that growing season and start the exploration of different options, one you may come across that seems overly similar is the different types of growing tunnels. For the most part many of these have simple designs and look very close like between the different types. We are going to focus on the differences between the High Tunnels (also referred to as Hoop Houses) and Caterpillar Tunnels. Between these two there are three major differences that stand out – permanence, structural soundness, and cost. Overall though, tunnels no matter the kind fit a nice middle ground for many gardeners and farmers as they deal with the much higher cost of building a greenhouse and being larger to grow in than cold frames.
Difference Between Tunnels
The caterpillar tunnel received its name because of its close resemblance to a caterpillar. It has segmented sections and cone-shaped ends that hug the ground at either end, usually held together by a stake and rope. The plastic is secured down by side-to-side crisscrossing nylon rope anchored to the base of each pole (where they touch the ground). It does not have built-in endwalls and is considered a temporary/movable option, allowing it to be one of the cheapest and quickest options. Many market gardeners use it as a starting point, often than later converting the caterpillar tunnel into a high tunnel greenhouse.
A high tunnel or hoop house, on the other hand, does have endwalls, doors, and sidewalls. Instead of a rope system, the structure is secured by metal base and hip board, side-braces, and purlins. The hoop house is then anchored to the ground by heavy-duty metal ground posts. The plastic is secured by metal lock channel and PVC spring wire, giving more stability and reliability. With the installation of hand cranks, the plastic sidewalls are often made to roll up and down, allowing for easy ventilation. This type of infrastructure is an investment meant to last for many years as they are a more durable, long-lasting option. Read Prequel to Building Your First Hoop House to learn more about how to build hoop houses.
Some of the basic points that work for either type of tunnel that can add or decrease the cost is the type of covering used on them. The four main types of covering used are: UVA protected 6 mil. plastic sheeting, Frost blankets, Insect netting, and Shade cloth.
A basic caterpillar tunnel can usually be built for around $1.00 per square foot. This reflects the recent dramatic increases in raw materials costs that we have seen across industry since the pandemic has caused shortages and shipping delays. In the recent past it was possible to build one of these for closer to $0.55 per square foot and we are hopeful that prices could return to this level in the next year or two.
A DIY hoop house kit can be an affordable starting point for many farms for season extension. A basic kit can be purchased for under $500 to be built with materials from your local hardware store. If you are looking for a more heavy-duty all-metal hoop house, you can buy all inclusive kits like the Bootstrap Farmer All-metal Greenhouse kits, without any need to get supplies from your local big box store.
Due to the reliability of these structures the USDA has put into place a grant program to help alleviate the investment costs of adding hoop houses to a farm’s operation. This program is called the NRCS High Tunnel Initiative and qualifying hoop houses are funded by this program for many growers around the country. Because this piece of infrastructure can sustainably extend the growing season for many farmers it helps increase food security. Because it improves and protects soil conditions it is supported by funds set aside for soil conservation.