We installed the low tunnels about 10 days after planting: May 18 & 19, 2016.
The primary benefit of using low-tunnels is to keep moisture off fruit, decreasing the incidence of fruit decay and increasing marketable yields, and to create an environment with more optimal growing temperatures as we enter the fall (in year one), and early spring (in year two). In our study at UNH, we are also trialling four different low-tunnel plastics that modify the amount and type of light (UV-A, UV-B, far-red, and infra-red) that reaches the plant and fruit. The findings from our research will be made available to growers and the public at the conclusion of the study.
While this is a focus of our research here at UNH, it does not affect low tunnel installation, and a standard agricultural-grade plastic would be appropriate for any low-tunnel installation, especially if the objective is to provide protection from water. In fact, a 2 mil plastic would be the easiest to handle and install in this case, but it probably will not provide the insulation that a 6 mil will, come fall. This year we are all utilizing 6mil plastics. Other materials are as follows:
- Dubois Agrinovations BROCH28 low-tunnels, hoop grounding stakes, and bungees
- 6 mil plastic, with about 5' extra on each end for tying off
- 14" and >24" heavy duty cable ties (home depot) [<-- We will address a better option than cable ties in a later blog post!]
- Wooden tomato stakes of at least 48" long or tunnel grounding posts provided by Dubois Agrinovations
1 - - Dubois recommends a 5' spacing for the low-tunnel hoops. Install these hoops through the field. However, do not install grounding stakes yet.
2 - - While plastics come in varying sizes, a 8' wide plastic fits these low tunnels well. We purchased 32' wide plastic and cut it appropriately. You will need to determine what length is required for your bed length, however, it is important to factor in at least 10-20' extra in length so you have enough slack at each end to tie off the tunnels to a grounding stake/tomato stake at both ends of each tunnel.
- Prior to covering the tunnels, we strongly recommend letting your plastic lay in the sun for at least an hour. It cannot be over emphasized how important it is to have the plastic covering taut, and this will help the plastic become more pliable prior to installation. If it is not taut, water WILL accumulate on the tunnel. Lowering the sides of the tunnel may decrease the occurrence of water accumulation, but since plants generally do not need protection from cold and there are no fruit during the spring of the installation year, to limit labor requirements we have elected to kept sides fully vented during spring rain. We will begin lowering sides during rain when fruit is present.
3 - - Hammer grounding stakes / wooden tomato stakes as deep as possible, at a 45* angle, at both ends of each row about 4' from the last hoop. This is what the plastic will be tied off to.
4 - - Pull plastic over low-tunnel. At one end, gather the plastic and synch it with a 14" cable tie (this is far quicker than using twine, and saves your back). Prior to completely tightening the tie around the plastic, run a larger (~48") heavy duty cable tie through the 14" tie [see a later post for an alternative solution]. This can be hooked around the grounding stake, and if loose enough, will allow you to tighten the tunnels as the plastic stretches. Tying the plastic off a couple feet off the ground will help keep the top of the tunnel taut.
5 - - At the other end of the tunnel gather the plastic with your hands and pull it as tight as possible. It is more important that the top of the tunnel be taut than the sides. Synch it with a 14" cable tie at a distance from the stake that can be reached by the cable tie. Loop the cable tie over the second grounding stake and tighten it, pulling the plastic as taut as possible.
There may be better ways to attach your plastic to a secured post/stake at the end of each tunnel, such as a ratchet [which we discuss in a later post]. The important thing is to be able to tighten the plastic easily as it stretches during the season because it will likely need to be tightened if it is a 6 mil plastic. We have not trialed a 2 mil, and are unsure how frequently that needs to be adjusted.
6 - - Once plastic is on bungees can be installed by hooking them over the little hoop at the base of the low tunnel. Hook it over one side, stretch it over the top, and hook it to the other hoop. This will help provide some tension to keep the plastic in place.
7 - - Next, the low tunnel grounding stakes that are meant to keep the hoops in place (different from the grounding stakes we use at the ends of the tunnels, which need to be larger!) should be hammered into the ground so that the hoop at the base of each stake is secured to grounding stake. These grounding stakes are very helpful in keeping the tunnel secure, especially in windy conditions. We installed one on every hoop, but switched back and forth from side to side.
The sides of the tunnels can be raised to any height. We have found folding the plastic under as you raise it, as opposed to simply bunching the plastic, will help ensure the top of the tunnel is taut and help encourage water to run off during rain storms.