Hoop House, Greenhouse, Caterpillar Tunnel, what is the Difference?
To ease confusion let’s look at the definitions of a caterpillar tunnel, a hoop house, and a greenhouse across the industry.
What is a Caterpillar Tunnel?
A caterpillar tunnel is a temporary growing structure, designed to be a low cost startup. It can be easily moved, as it has almost no bracing. Instead of wood or metal bracing, the caterpillar relies on a webbed rope system to adhere the plastic and maintain its structure. At its most basic package, a strap or webbing material is used in place of a metal purlin. The basic packages are staked down with rebar instead of 2”+ diameter metal poles, which offer less surface area holding the post into the ground. There are also no doors as the end walls consist of bunching extra plastic and staking it into the ground.
What is a Greenhouse?
A greenhouse is on the opposite end of a caterpillar tunnel when it comes to cost and permanence. Greenhouses typically have hard side endwalls made of insulated polycarbonate. Greenhouses employ stages of cooling like powered gable vents, wet walls, exhaust fans, thermostat or computer monitored controllers, gas heaters, and some type of shade deployment. The larger width size, think 24’ plus, make greenhouses engineered structures. This adds to material size and expense to install. You can often figure in extra expenses for concrete foundations and more construction costs to install. In use, greenhouses are often intended for year round mono-cropping and ready to serve an existing revenue stream. They are also popular in educational and research farms as the inside working environment is better for isolating experiments and more comfortable for students and staff throughout the year.
What is a Hoop House?
A hoop house captures the best of both caterpillar tunnels and greenhouses. You get the structural integrity of ground posts, hip and baseboards, solid ridge poles, and end walls with doors without the added expense of engineered truss systems. This is because hoop houses are generally 20’ wide or less.
Some DIY’ers ask about going wider than 20’. We discourage that as the material used to make hoop house bows tend to be as low as 18 gauge and stop at the 16 gauge mark. Even if you used a bigger pipe you still would need internal trusses to span the width of the structure. You can achieve the desired square foot by going longer because of the hip/base/ridge pole configuration but the width will be the weak point without internal bracing and thicker poles all placed precisely to carry the load.
When a hoop house is being used for its intended purpose of extending a growing season, options like: roll up sides, double layer plastic, and four season farming via crop variety rotations make the middle of the road price point very attractive.
Add stronger build, minimal time to set up, and weather protection and it's easy to see why more people choose to invest a couple of extra build days into a longer lasting structure. Peace of mind is a pretty valuable commodity in farming when there are constant surprises that are out of our control.
What are the benefits of building a hoop house?
*Please note, a hoop house doesn't provide a license to grow everything in the seed catalog :) Hoop houses are limited by ambient temperature, daylight hours and the quality of the soil.
For seasonal extension, It is a good idea to reframe your crop selection to your local market. Hoop houses give you the ability to plant transplants into the ground as much as a few weeks earlier. In the case of longer term vine crops, this means earlier blooms and perhaps the ability to have the first tomatoes of the season at the market. Earlier plantings may give you more turns (number of harvests) of leafy greens.
For cut flower farmers, who could benefit from underwatering and petals protected from rain and wind damage, a hoop house may mean earlier perfect cut flowers in early spring. It could mean, having product when commanding market prices are available to add to the year’s bottom line.
Think earlier harvests, later harvests, and off season options like: cold hardy crops, soil building through cover cropping, and better produce protection throughout the entire season.
Hoop house construction timing can mean the difference between a stressed out season or actually using the structure in an ideal manner. Considering your first and last frost dates will help you to decided the best time to have a completed hoop house.
Trying to build a hoop house in the winter for a winter crop means you will be rushing the build, planting later than a full crop cycle can happen, and most likely ordering when suppliers are at full capacity.
Trust me when I tell you that suppliers get slammed with orders for greenhouse film adding to cut times. The same thing happens in the summer when temperatures spike for the first time. The best thing you can do is never let any supplier dictate when you will get a critical piece of equipment. There is no better example than the mass agricultural industry hit during the Spring of 2020. Covid-19 delays and then out of stocks everyone was affected by.
Be prepared before you need something or be flexible in the busy season. Having a mindset of flexibility and preparedness will in general make you a better farm business owner.
Of note: High Tunnels are an offshoot of a hoop house that typically describe taller sidewalls and bigger doors for larger equipment. The terms; hoop houses, poly tunnels and high tunnels are interchanged a lot.
There are about as many ways to piece hoop houses together as there are farmers. There lies the beauty of building your own. Even when building from kits, there are countless options to customize it for your needs.