catepillar Tunnels

We get the question a lot on “What are those white tunnels in your garden?” And this is the blog post to explain that answer.

Those tunnels, most often found in our garden covered with white row cover, are called caterpillar tunnels. Caterpillar tunnels are used for many crops and many purposes. They can be covered with poly early and late in the season to provide a warm environment. They can be covered with shadecloth in the summer to grow cool-loving flowers and plants. When covered with row cover (Agribon) or insect mesh, they can be used in summer to exclude pests.

Caterpillar tunnels over spring beds in 2022.

These tunnels are easy to build and move and offer season extension and protection for our flower crops. Caterpillar tunnels are a low-cost alternative to traditional hoop houses and offer many of the same benefits as well as some additional ones.

Caterpillar tunnels are much smaller than most hoop houses. Our tunnels are about 4 feet high and 5 feet wide, and 50 to 60 feet long. The tunnels are constructed from 10-foot pipes, bent in an arch, these are the “hoops”. When the cloth is laid across the top of the hoops, secured down to the ground by sandbags, it creates a caterpillar-like appearance that gives the tunnel its name.

Here are several of the key reasons we use caterpillar tunnels on our farm:

1. Season Extension

In Kokomo, Indiana our traditional last frost date is April 30 and our first frost date is October 6, leaving us with 5 and a half-ish months of an outdoor growing season. Many of the specialty cut flowers we grow are not native or hardy to the Midwest and our Zone 5 growing conditions, therefore we grow many varieties as annuals. Meaning our cooler winter temps or hot dry late summers may not be ideal growing conditions for some of these plants. Caterpillar tunnels give us the flexibility to create a more favorable growing condition for specific varieties.

We plant out many varieties of cool flowers, flowers that like cooler temps and that can withstand a little below freezing temps, in the fall or very early spring (March-April). Without caterpillar tunnels and the flexibility of covering these flowers with frost protection cloth for warmth and snow/wind protection, many of these wouldn’t survive well. We can also cover late summer crops in October if frost is threatened early to extend our growing season a bit.

We do not have any hoophouses or greenhouses on our farm currently. These caterpillar tunnels give us many of the same benefits as traditional larger hoophouses, but at a fraction of the cost and additional flexibility!

2. Moving the Tunnel

Secondly, unlike traditional hoophouses, caterpillar tunnels are designed to be relatively portable. Two people can set up the tunnel in an hour and take it down in approximately the same amount of time. This portability comes with several advantages. If you live in a climate with a harsh winter, for instance, you can easily take off the plastic to prevent wear and tear throughout the winter, or even take down the entire house.

You can also move your caterpillar tunnel around the garden throughout the growing season to cover different crops at various stages of growth. We reuse the pipe hoops on several rows throughout the growing season, covering them with different materials based on the crop growing underneath. The cloth coverings fold up or roll up easily for storage. The pipe hoops pull out easily and are substantial enough that they don’t bend or twist easily, yet light enough to store and transport fairly easily.

3. Crop Protection

Caterpillar tunnels also allow us to protect our flowers from frost, wind, rain, sun, and pests. Sping and fall in Indiana usually brings unstable weather at times. High winds and heavy rain often occur in the spring and can be detrimental to young seedlings! Hot late summer sun, especially reflecting on the black landscape fabric we use for weed control, can choke out plants fast. And some of our flowers are very susceptible to certain bugs and pests. All of these non-ideal conditions can be managed with row covers, shadecloth, and greenhouse film coverings over our caterpillar hoops.

Agribon

We used agribon (AG-19) as a favorite for covering rows for frost protection. AG-19 protects crops down to 28°F and is the standard grade for general frost protection. With 85% light transmission and a permeable fabric, it allows both light and precipitation through the material while offering light protection from direct sun and heavy rains. We have heavier agribon material also we can use for cooler temps, and multiple layers of agribon can also be used at once for added protection.

Agribon can also be used for pest protection and flower rows can be covered to keep out leafhoopers (which carry aster yellows, a disease that damages many flowers in the Aster family), grasshoppers, aphids, and other pests.

Shadecloth

Shadecloth is also in our arsenal of hoop covering materials. It reduces soil temperatures, prevents sun damage, speeds the growth of cool weather crops, and protects against wind damage and desiccation. The knitted shade cloth is lightweight and provides shade to reduce the temperature around plants by 10 degrees or more.

Greenhouse Film

We also have a little poly, clear, greenhouse film to cover a row or two if need be. We’ve used this in years past to grow flowers early for weddings. UV resistant and ultra-clear, designed specifically for greenhouses, it provides optimum light transmission and is extremely durable for long winters. The greenhouse film does not allow rain or any wind or material through it and underneath heats up quickly in sunlight.

There are other options for hoop covers, but the three above are the only ones we used on our farm to provide protection to our flowers.

Above images of covering materials are pulled from Johnny’s Selected Seeds.

4. Soil Health

Additionally, the portability of caterpillar tunnels also helps maintain soil health. Because it doesn’t rain inside traditional hoophouses and high tunnels, soluble salts including nitrate, potassium and sulfate can accumulate in the soil over time. With a caterpillar tunnel, this problem is avoidable by removing the plastic from the tunnel a few times throughout the year for a period of several weeks, or by moving the caterpillar tunnel back and forth between different locations.

We use our caterpillar tunnels for a short period of time, usually less than a 2-month period in any one location. And because of crop rotation and our garden layout, our cut flowers are never in the same location two years in a row, unless they are perennials. So the soil gets worked and exposed just like it would in any other outdoor application - amendments are made, beneficial insects are present, and the soil health is maintained.

Ranunculus growing under a caterpillar tunnel. (Photo from Floret)

Benefits specific to cut Flowers

Growing cut flowers in caterpillar tunnels also results in longer stems and higher quality blooms in certain seasons and varieties. Ranunculus and anemones are cooler-season flowers and usually bloom from late May to June for us. If the summer warms up too quickly, shadcloth or row cover can be used to provide cooler temps and extend the ranunculus and anemone season by up to a couple of weeks. Lisianthus is also another example where row covers can be useful outside of frost protection. Lisianthus has many layers to the blooms, much like a rose, and heavy dew or rain can make the blooms top-heavy and snap. Row covers help reduce this issue and also provide some shade, forcing the lisianthus stems to extend and grow longer.