by Skip Paul, Wishingstone Farm, Little Compton, RI.
With hurricane season upon us and Sandy potentially heading our way it’s time to think about preparing your greenhouses to survive the high winds we might be seeing soon. The article below contains some advice from Skip Paul of Wishing Stone Farm, who grows his crops on the coast of Rhode Island and has some experience with surviving heavy weather. Also, remember that before a rainstorm is an important time to apply fungicides for managing diseases, but sufficiently before so there is time for the spray deposit to dry and become rainfast (check the label). Development of most fungal and bacterial diseases is promoted by storms as they provide ideal conditions for pathogen dispersal and infection, with the notable exception of powdery mildews. Lastly, the MDAR Division of Animal Health is reminding everyone that establishing a plan of action in preparation of any type of emergency can minimize injury and property loss. A template to assist you in developing a farm emergency plan is available on our website at http://www.mass.gov/eea/agencies/agr/animal-health/farm-emergency-plan/
How to Prepare
Hurricane preparedness should start with checking all your connections and structural members every time you change your plastic (every four years). For instance if there is a weak link in a chain and a nut vibrates off of a critical connection, you will start a cascade of other failures. Take the two hours required to check and evaluate the connections on your houses between coverings. Don’t just throw on another covering and call it done. Evaluation includes cleaning the bugs out of your inflation fans. Keeping the two sheets a bit over inflated during a storm is a good thing. This requires patching the myriad of small holes and nicks. We just open up the inflation fan air intake (all the way) and get that plastic extra tight. Don't forget to readjust the inflation fan intake slide vent after the storm - you don't want to over stretch your plastic. It will shorten its life over time.
The next biggest problem is junk around the farm that can get going in the wind and rip a hole in the plastic, which leads to the next most important thing: don't let the wind get in the structure. The wing on an airplane lifts as much from the wind speed of the wind going over the top and lifting the wing from the rear as it does from getting under the wing. In a similar way, the air going over the top of the greenhouse wants to lift the downside. Buttoning up the structure will help keep the air from doing this. Obviously, keeping the wind from getting inside is important as well. If we know we will lose power, we duck tape the intake shutters to keep the wind out. Keep your large doors closed by putting something in front of them. Most greenhouses don't have good door latches for their doors; if they vibrate loose or fail, wind will get in.
Probably the most important decision is whether to cut or take off the plastic. I once heard that the increase of wind pressure or damage increases 80% when you go from 75 mph to 100 mph. If you add rain water to that, you have a force most of us have never experienced. We have always thought that if we know we are getting 100+ mph winds then we should take the plastic off...the structural damage to the greenhouse doesn't warrant trying to make it through the storm. Plus, at 100+ mph you probably will lose your power and there is another reason you will be glad you took the plastic off. Uninflated greenhouse coverings are like a large boat spinnaker gone wild...It can be dangerous and just beat the hell out of the structure. Tip: if you do take the plastic off; try to do it in two separate pieces and put it away somewhere dry. If you let it slump off the greenhouse and fill with water, the capillary activity of the water between the sheets will make it impossible to recover the house until they are separated and dry.
People with Haygrove (that includes us). Don't even think about trying to make it through anything over 65 mph. Your manual will tell you it isn't made for that kind of wind. Especially since their solution to lower wind speeds is to open the structure up! That can work up to 55 mph, but above 65 the wing on the airplane physics kicks in and you will be sorry. Our Haygrove had one end crushed in a sudden wind gust last season; it can happen. Those with Rimol moveable houses (or greenhouses on skids a la Elliot Coleman) should heed the same warning: like the above airplane wing conclusion, small pipes driven in here and there will do you no good when the wind gets over 75 mph. It’s better to take the plastic off than to see your greenhouse rolling over your neighbor’s hayfield.
Probably the most important thing is to respect the peak of the storm. Don't switch plans and try to do any of this in the midst of the storm. The wind is dangerous and adding heavy rain to that can be catastrophic…I once saw a sailor flipped 30 feet into the air while trying to hold a spinnaker line that got loose. Be careful with this storm.