liz stevens
Lovin' The Homestead
These tips come from our own hard lessons learned in building a hoop greenhouse.
A hoop green house is one of the cheapest methods to build for a small backyard to a large commercial size greenhouse grower. They look easy to build but there are some things you will want to know to prevent making the same mistakes that we did.
Hoop green houses are constructed of metal or PVC tubing formed in a radius supported with cross bracing and then covered with plastic. Most sustainable gardeners will want a small one to start plants and hold over potted plants and flowers for the winter.
Lesson #1- dont purchase your plastic at the local hardware or building supply store. The clear plastic sold in these stores just will not hold up to the UV rays and within a year, maybe two if your lucky, will dry out and tear off like paper.
Instead purchase plastic made for green houses. You can find it at greenhouse suppliers such as Growers Supply http://www.growerssupply.com/farm/supplies/prod1;gs1_greenhouse_building_materials;pg108654.html You can buy it by the foot from 6 wide to 64 wide. The plastic 10 wide runs $2.39 a foot. This plastic is rated for four years; We actually had it last much longer. Buy the plastic to have one continuous run from side to side so that it can be stapled or fastened for an air tight seal. Save some of the scraps to silicone over tears that will occur when the kids get too close with the lawnmower.
Lesson #2- Double up the plastic and seal the edges so that you can induce air between using a small fan. This will provide a very strong greenhouse that you wont have to worry about during high winds, rains, and snow. The plastic balloons up to where you can bounce a coin off of the top. The convex shape sheds water and snow so it wont begin to pool and break through the top. The air space also provides an extra insulating factor. I worked in our little green house in some pretty wild weather and was very satisfied with the structural integrity this provided. In fact I think you could make a temporary living shelter with this same concept.
Be sure to check all your tube framing looking for rough edges or sharp points that might tear into the plastic. Just a screw head that has been stripped leaving some metal shaving sticking out can tear the plastic. We used rubber tape and covered all the screw heads and other areas that might be a problem.
It doesnt take much to inflate a greenhouse, in our little 8 x 12 greenhouse we used just a 4 x 4 muffin fan, like they used on some of the earlier electronics. http://www.surpluscenter.com has them in both 110 volt and 12 volt the 12 volt item #16-1380 is $5. If you are building a larger greenhouse go with item# 16-1378. This is the same type of fan sold for commercial greenhouses and at only $49.99 is probably at least $30 cheaper than it will cost you from a green house supplier. It also comes with a mounting flange.
If you havent discovered Surplus Center yet they have a large source of all types of electrical, hydraulics, motors, fans and etc. for the Self-Sufficient DIY inventor and project person. We purchased all the components needed when we built our log splitter. You can also order over the phone at 1-800-488-3407. They also have other fans and blowers as well.
You can mount the fans onto a plywood base that is secured anywhere to one of the hoops or shelving system. Simply drill or cut a hole the size of the fan output side and then carefully cut through the inside layer of plastic and secure it with a bead of clear silicone. Add a screen cover on the intake side to prevent bugs and other debris from being blown in between the plastic.
If you frame in and use plastic on the ends of the greenhouse you can also use 1-1/2 flex plastic pipe (like the cheap discharge pipe sold with sump pumps) to inflate the ends. We drilled holes the size of the pipe in some plywood blocks and then silicone one side to the main pressurized side and the other to the end cap that I wanted to pressurize. You can add these jumpers anywhere and use the air off just the one fan.
Treated 4 x 4 works best to use on a base of gravel for the foundation. This allows you to make or purchase bolt on brackets to hold the ends of the hoops, as well as roll the edge of both plastic sheets and staple them along the bottom edge. We then used some plastic stripping to screw on the top.
On the ends caps using 3-1/2 strips of exterior grade plywood glued and laminated to duplicate the hoop radius and height will allow you to roll staple and add a screw on a plastic strip to secure the plastic onto the ends.
Once you figure out the hoop size and height you want, lay one down on a concrete pad and outline it in chalk. Cut your base from a 4 x 4 treated board cut to length (width of the greenhouse less the thickness of two layers of plywood on each side) and then cut two wood studs for each end cap. Space the studs to accommodate a door on one end, (I used an old aluminum storm door), and on the back end I spaced to accommodate an attic ventilation fan.
Miter the tops of the studs to match the radius as close as possible. Cut the studs overall length to accommodate two layers of the plywood so that the top will match the height of your hoops. Begin attaching one section of plywood strip on each end of the 4 x 4 and bend it in the shape of the radius and glue and screw it to the top of the studs, ( add a spacing block to keep the studs evenly spaced at the top)
After this is completed glue a second layer over the top to cover over the splice, and then add sections on each side to complete the radius. Once the basic shape is completed fill in with other studding and blocking. This is a good time to plan out the height of your shelving and add blocking on each end to accommodate shelf runners on each side to rest on the blocking. This will also add end to end strength to the greenhouse.
We actually painted our framing before assembly to make it look nice through the clear plastic and to hold up for year. Once completed the end caps can be lagged bolted to the 4 x 4 sides foundation.
Keep in mind you will also want to inflate the ends, so dont staple the plastic on to the blocking and studding. Just roll and staple the bottom edge and the radius.
Lesson #3- These greenhouses heat up fast and get cold at night. You will want to add a thermostatic power ventilator, such as the ones sold for gable end attic ventilation. Purchase the self closing louver to go with it. This goes in the top of the back end cap where you framed for it. Add a top and bottom blocking so it will screw securely all the way around. Then build a 1 x 4 frame on the outside and add a wood door to close off during the colder nights.
On the door end toward the bottom add an intake door or doors on each side of the walk in door. Build the same outer door to close off for cold nights and add a heavy flap like a truck mud flap on the inside so that it will pull back when the fan comes on. (We were a bit more tech and added a power opening spring loaded ventilator shutter wired into the fan circuit, this prevented any cold air from blowing in on those cold sunny days when we couldn't shut the outer doors). Do add a chain hook on the outer doors so they dont blow back and forth or close when the fan is on.
It doesnt take much to heat the greenhouse on cloudy winter days or cold nights. You just need to keep the plants from freezing. For plant starters we used old water bed heat strips under the seed trays. We used a small wall mounted propane heater, for when we were gone overnight. But we also hooked an old school bus back seat heater into our outdoor wood burning stove and pumped hot water through it for most of the heating. We added a thermostat on and converted the fans to 110 volt, but maybe the 12 volt fans could still be used with a good battery and high output solar charger.
Lesson #4- Plants will dry out quickly and will need frequent watering, sometimes as much as twice per day. Some planning of a water source that will not freeze needs to be considered as hauling in a sprinkling can, will get pretty old. If you are able to build the greenhouse over the top of a frost proof hydrant you will solve this problem. We ended up with a large plastic sprayer tank equipped with a 12 volt pump and a sink sprayer with additional hose. This meant we still had to hose over and fill the tank, but we did so on the better and warmer days.
We actually believe overall allowing the water to sit in the tank and to become warm created less shock to the tender plants than hitting them with cold water directly out of a hose. If you do use a water hose, you will want a fine mist sprayer so you dont blast the potting soil out of the pots or bend over and break off the plantings. We ran salvaged lumber to form slats to run across the 2 x 4 shelf runners. With a gravel floor we were able to soak the plants and didnt have to worry about solid shelving holding the water. Hanging plants were hung from the hoops or bracing.
Lesson #5- You will want to use sanitized or sanitize your potting soil. Heat the bags up under black plastic for an extended time. Believe us getting rid of bugs that hatch out in the potting soil in a green house is not an easy task to do.
Lesson #6- Green houses do not have natural pollinators like an outdoor garden. Bees will either be in hibernation or unable to drop in and cross pollinate your plants. If you plan on trying vegetables you will want to study up on plants that need pollination to bear fruit and how to hand pollinate them. It is rather easy using a cotton tip swab. Since it took us weeks and weeks to finally produce one small tomato we wont claim to be an expert on pollination. We just know it is part of the process and needs to be done for indoor growing. So you will need to do your own research on this.
Hope you enjoy many years with your own hoop green house. Sorry we dont have photos to share; we built this about ten years ago before digital cameras were so available. We currently now have a potting shed with windows for our plants.
A hoop green house is one of the cheapest methods to build for a small backyard to a large commercial size greenhouse grower. They look easy to build but there are some things you will want to know to prevent making the same mistakes that we did.
Hoop green houses are constructed of metal or PVC tubing formed in a radius supported with cross bracing and then covered with plastic. Most sustainable gardeners will want a small one to start plants and hold over potted plants and flowers for the winter.
Lesson #1- dont purchase your plastic at the local hardware or building supply store. The clear plastic sold in these stores just will not hold up to the UV rays and within a year, maybe two if your lucky, will dry out and tear off like paper.
Instead purchase plastic made for green houses. You can find it at greenhouse suppliers such as Growers Supply http://www.growerssupply.com/farm/supplies/prod1;gs1_greenhouse_building_materials;pg108654.html You can buy it by the foot from 6 wide to 64 wide. The plastic 10 wide runs $2.39 a foot. This plastic is rated for four years; We actually had it last much longer. Buy the plastic to have one continuous run from side to side so that it can be stapled or fastened for an air tight seal. Save some of the scraps to silicone over tears that will occur when the kids get too close with the lawnmower.
Lesson #2- Double up the plastic and seal the edges so that you can induce air between using a small fan. This will provide a very strong greenhouse that you wont have to worry about during high winds, rains, and snow. The plastic balloons up to where you can bounce a coin off of the top. The convex shape sheds water and snow so it wont begin to pool and break through the top. The air space also provides an extra insulating factor. I worked in our little green house in some pretty wild weather and was very satisfied with the structural integrity this provided. In fact I think you could make a temporary living shelter with this same concept.
Be sure to check all your tube framing looking for rough edges or sharp points that might tear into the plastic. Just a screw head that has been stripped leaving some metal shaving sticking out can tear the plastic. We used rubber tape and covered all the screw heads and other areas that might be a problem.
It doesnt take much to inflate a greenhouse, in our little 8 x 12 greenhouse we used just a 4 x 4 muffin fan, like they used on some of the earlier electronics. http://www.surpluscenter.com has them in both 110 volt and 12 volt the 12 volt item #16-1380 is $5. If you are building a larger greenhouse go with item# 16-1378. This is the same type of fan sold for commercial greenhouses and at only $49.99 is probably at least $30 cheaper than it will cost you from a green house supplier. It also comes with a mounting flange.
If you havent discovered Surplus Center yet they have a large source of all types of electrical, hydraulics, motors, fans and etc. for the Self-Sufficient DIY inventor and project person. We purchased all the components needed when we built our log splitter. You can also order over the phone at 1-800-488-3407. They also have other fans and blowers as well.
You can mount the fans onto a plywood base that is secured anywhere to one of the hoops or shelving system. Simply drill or cut a hole the size of the fan output side and then carefully cut through the inside layer of plastic and secure it with a bead of clear silicone. Add a screen cover on the intake side to prevent bugs and other debris from being blown in between the plastic.
If you frame in and use plastic on the ends of the greenhouse you can also use 1-1/2 flex plastic pipe (like the cheap discharge pipe sold with sump pumps) to inflate the ends. We drilled holes the size of the pipe in some plywood blocks and then silicone one side to the main pressurized side and the other to the end cap that I wanted to pressurize. You can add these jumpers anywhere and use the air off just the one fan.
Treated 4 x 4 works best to use on a base of gravel for the foundation. This allows you to make or purchase bolt on brackets to hold the ends of the hoops, as well as roll the edge of both plastic sheets and staple them along the bottom edge. We then used some plastic stripping to screw on the top.
On the ends caps using 3-1/2 strips of exterior grade plywood glued and laminated to duplicate the hoop radius and height will allow you to roll staple and add a screw on a plastic strip to secure the plastic onto the ends.
Once you figure out the hoop size and height you want, lay one down on a concrete pad and outline it in chalk. Cut your base from a 4 x 4 treated board cut to length (width of the greenhouse less the thickness of two layers of plywood on each side) and then cut two wood studs for each end cap. Space the studs to accommodate a door on one end, (I used an old aluminum storm door), and on the back end I spaced to accommodate an attic ventilation fan.
Miter the tops of the studs to match the radius as close as possible. Cut the studs overall length to accommodate two layers of the plywood so that the top will match the height of your hoops. Begin attaching one section of plywood strip on each end of the 4 x 4 and bend it in the shape of the radius and glue and screw it to the top of the studs, ( add a spacing block to keep the studs evenly spaced at the top)
After this is completed glue a second layer over the top to cover over the splice, and then add sections on each side to complete the radius. Once the basic shape is completed fill in with other studding and blocking. This is a good time to plan out the height of your shelving and add blocking on each end to accommodate shelf runners on each side to rest on the blocking. This will also add end to end strength to the greenhouse.
We actually painted our framing before assembly to make it look nice through the clear plastic and to hold up for year. Once completed the end caps can be lagged bolted to the 4 x 4 sides foundation.
Keep in mind you will also want to inflate the ends, so dont staple the plastic on to the blocking and studding. Just roll and staple the bottom edge and the radius.
Lesson #3- These greenhouses heat up fast and get cold at night. You will want to add a thermostatic power ventilator, such as the ones sold for gable end attic ventilation. Purchase the self closing louver to go with it. This goes in the top of the back end cap where you framed for it. Add a top and bottom blocking so it will screw securely all the way around. Then build a 1 x 4 frame on the outside and add a wood door to close off during the colder nights.
On the door end toward the bottom add an intake door or doors on each side of the walk in door. Build the same outer door to close off for cold nights and add a heavy flap like a truck mud flap on the inside so that it will pull back when the fan comes on. (We were a bit more tech and added a power opening spring loaded ventilator shutter wired into the fan circuit, this prevented any cold air from blowing in on those cold sunny days when we couldn't shut the outer doors). Do add a chain hook on the outer doors so they dont blow back and forth or close when the fan is on.
It doesnt take much to heat the greenhouse on cloudy winter days or cold nights. You just need to keep the plants from freezing. For plant starters we used old water bed heat strips under the seed trays. We used a small wall mounted propane heater, for when we were gone overnight. But we also hooked an old school bus back seat heater into our outdoor wood burning stove and pumped hot water through it for most of the heating. We added a thermostat on and converted the fans to 110 volt, but maybe the 12 volt fans could still be used with a good battery and high output solar charger.
Lesson #4- Plants will dry out quickly and will need frequent watering, sometimes as much as twice per day. Some planning of a water source that will not freeze needs to be considered as hauling in a sprinkling can, will get pretty old. If you are able to build the greenhouse over the top of a frost proof hydrant you will solve this problem. We ended up with a large plastic sprayer tank equipped with a 12 volt pump and a sink sprayer with additional hose. This meant we still had to hose over and fill the tank, but we did so on the better and warmer days.
We actually believe overall allowing the water to sit in the tank and to become warm created less shock to the tender plants than hitting them with cold water directly out of a hose. If you do use a water hose, you will want a fine mist sprayer so you dont blast the potting soil out of the pots or bend over and break off the plantings. We ran salvaged lumber to form slats to run across the 2 x 4 shelf runners. With a gravel floor we were able to soak the plants and didnt have to worry about solid shelving holding the water. Hanging plants were hung from the hoops or bracing.
Lesson #5- You will want to use sanitized or sanitize your potting soil. Heat the bags up under black plastic for an extended time. Believe us getting rid of bugs that hatch out in the potting soil in a green house is not an easy task to do.
Lesson #6- Green houses do not have natural pollinators like an outdoor garden. Bees will either be in hibernation or unable to drop in and cross pollinate your plants. If you plan on trying vegetables you will want to study up on plants that need pollination to bear fruit and how to hand pollinate them. It is rather easy using a cotton tip swab. Since it took us weeks and weeks to finally produce one small tomato we wont claim to be an expert on pollination. We just know it is part of the process and needs to be done for indoor growing. So you will need to do your own research on this.
Hope you enjoy many years with your own hoop green house. Sorry we dont have photos to share; we built this about ten years ago before digital cameras were so available. We currently now have a potting shed with windows for our plants.
I found with the one I just took down that during the summer it was just simply too hot to even enter even with fans venting it. We made the ends to roll up and help keep it cool in summer.
