Even though we have our glass greenhouse, the Rvalue on it is actually pretty low: around 0.91! Actually, the Rvalue on this doubleplastic hoop design is higher, coming in at around 1.3 to 1.4, and if you added a layer of bubble wrap it would be even higherthis structure is actually easier to heat than our bigger greenhouse!

This makes it ideal for hardening off seedlings that are almost ready to go out but still need a bit of protection, or growing on seedlings that need additional heat. While the temps won't stay even enough for germination, you could germinate inside and then move your seedlings out to this space (if you use the supplemental greenhouse heater). In our tests, the structure as built holds temps about 22 to 25 degrees F higher than outside air temps, so when it is 27 degrees F outside, the greenhouse holds around 48 F at night. During the day, the temps warm up quite well and you will likely need to ventilate the sides to help prevent overheatingso if you are using it as a greenhouse and you work during the day, remember to ventilate it so you don't roast your plants!

You can also use this hoop structure minus the space heater to extend your growing season. Usually a structure like this lets us plant about 2 weeks earlier and will protect from any unexpected frosts that may occur. We leave the hoops up all year as we can always use them to throw some netting over in case of hail!

Remember, if using a greenhouse heater, be sure to keep 3' clear of combustible items, in this case leaves or debris, and use an outdoor rated cord. Always follow space heater safety protocol. :)

Materials list for a 4x8' bed:
10 pieces of 1/2" by 24" or 18" long rebar
15' of nylon cord
4 hoops, 10' long (PVC if you don't have a hoop bender, or electrical metal conduit if you have a hoop bender like the one from Johnny's Seeds)
10'x25' sheet of greenhouse plastic, at least 7 mil but ideally 8 mil, from Johnny's Seeds or Greenhouse Megastore
Optional greenhouse space heater
Clamps like these (8 total, two per hoop)

Materials link: https://www.amazon.com/shop/blossoman...