FoxDog Farm: High Tunnel Greenhouse, 2009

A New High Tunnel Greenhouse

We knew we were going to need another greenhouse. The glass house that is attached to the southern side of our residence is big (12 x 30 ft) but not big enough to grow enough tomatos and peppers for our CSA and family needs. So we researched various other kinds of greenhouse and finally decided on a high tunnel hoop house. These hoop houses are constructed from PVC and greenhouse plastic and are meant to be temporary. They can be moved if necessary and are useful in the field or as a greenhouse.

The internet provided various plans, and we eventually went with the design available here. We felt that this plan had several benefits. The primary benefit is that it seems to be very sturdy. FoxDog Farm is windy (we call it Siberia) almost every day, because we have water on 3 sides of us. The plastic is removeable for the winter, if we so desire and this will enable the house to survive windstorms and snowstorms. The construction is simple, with simple skills required. The tunnel is roomy, and will provide enough room for our tomatos and other plants. The construction costs wouldn't run too high, although they did go a bit higher than we expected. In a pinch we can move this hoop house.

Siting

We decided to put the high tunnel near our glass greenhouse, so that it would be easy to transfer plants between the two. This also facilitates watering and any electrical needs we might have, although we forsee not needing electricity in the high tunnel and haven't planned for it. Therefore, the high tunnel is sandwiched between the goat area and the lawn, set amongst a few trees. The trees provide some shade, but it's only really a factor in the winter, when we don't think we'll be using the tunnel. In fact, the tunnel will probably have the plastic removed for the high winter.

Randy did a lot of work on the site we'd chosen as it had been something of a rough dumping ground previously. There was a lot of old farm junk there and dumps of excess gravel that we'd used in our herb garden. The willow tree/bush had to be cut back. The goats loved the trimmings!

Day 1: Setting up the Hoops/Bows

The plans called for an ingenious use of different diameters of pvc pipe to created the framework of the high tunnel. The hoops or bows are 1.5 inch pvc. They are set into 2 inch pvc anchors which are pounded into the ground. These are held stable by a framework of 2x6 lumber(the baseboards) and secured by carriage bolts. The plans linked to above are really good about explaining what is needed, although there is an error concerning this section of construction in the parts list. Ten 10ft long 2x6s are required, not 6 as listed in the parts list. Also, the carriage bolts for the purlins should be 5 inches long, not 4.5 inches. And you probably don't, or can't drive, 2.5ft of pvc anchor into the ground unless you have really silty ground. We have mucky clay with a hard clay layer about 1 to 2 ft down, and we couldn't drive them through the clay layer.

Our chosen site slopes down to the east. This is good because it makes drainage really easy. However, it also makes the construction a little unusual. We had to step down the baseboards and, eventually, the bows/hoops.

We quickly learned that the pvc will shatter if you drill too much through it. It sets in the bow shape very quickly and gets brittle under tension. We shattered and had to replace one bow after we tried to drill it the next day.

Day 2: The purlins and the hipboards

To stabilize the structure, and to create places to conveniently hang tomato strings, we wanted to put several purlins down the length of the hoop house. The central, and highest, purlin is secured by drilling down through the two pvc pipes (the purlins are pvc). The pipes are then held by carriage bolts. As mentioned above you really need 5 inch bolts for this, not 4.5 inch. Or, at least, we really needed them.

We got nervous about drilling through the bows after one shattered and decided to attach the two outside, and non-structural purlins by zip ties. We'll see how this works out, we might replace them with wire or some other kind of assembly.

The plastic which forms the cover of the hoop house is secured on hip boards which are about 3 ft above the baseboards. The plastic can be secured via lathe strips which are screwed down over it, or via wiggle wire strips. We used wiggle wire, so that the plastic would be easier to remove. The plastic is not screwed to the baseboard in order to provide an easy way to vent the greenhouse. The lower sides can simply be rolled or lifted and air can then enter the greenhouse when needed.

Days 3 and 4

Technically, it should be days 3 - 5, but we only did partial days work on all of them. Randy and Rikke built the endwalls on the third day. They were fairly easy to do, although we could have used a mitre saw at one point. We also added the lateral bracing from the end walls to the baseboards. This made things really sturdy.

The plastic greenhouse film comes with instructions as to how to put it on the house. Ours was delivered in a 'W fold', so that it was folded up from the edges along a center line. Instead of unfolding and pulling the whole thing over the bows of the house, the instructions said to feed it along the topline (the top purlin in this case) and let it unfold by itself. This worked like a charm, although it was rather difficult to feed it with only 4 people. Jodie and Rikke kept the film rolled up on a spare piece of PVC pipe, so that it wouldn't unfold. Dave stood in the back of the pickup and fed the film up to the purlin. Randy, the strongest of all of us, tugged it down the length of the purlin. Much cussing and panting did ensue, but it went on great.

After the plastic was on, we had to put the plastic on the endwalls. Randy and Rikke did this on the fifth day. It was pretty easy. We used a staple hammer and the wiggle wire channel, making sure that the top piece of plastic was not stapled, but only held by wiggle wire. This is so it's 'easily' removeable. Then we cut a door in the plastic and put up an old screen door we had laying around. We used the handy-man's friend, duct tape, to put the plastic on the door (we'll come up with something better later) and we were all done.

The greenhouse is very effective. It's steamy hot in there during the day, and it cools off fairly quickly at night. I would not grow anything in it in the winter, without using reemay as well. During July and August I expect that we'll have to vent it by lifting up the plastic along the side bottoms. Right now, that's not needed.