A few basic tips:
- Keep it close to the house: My hoop house is great for growing seedlings, but it's not very convenient. My hot box is set up on a picnic table right outside the back door (or as close as it can be and still receive sunshine). I can swap plants in or out in a few minutes. A deck or front stoop might be a good option.
- Avoid plant shock--especially at the beginning, the transfer from your house to shelter should not be too jarring. After plants get hardier I am more lax with this, but at the start I wait for temps above freezing outside, and in the cold frame at least as warm as indoors. For colder-hardy plants, I watch until the box hits 50ish degrees. Keep transfer times to a minimum.
- Related to this, keep an eye out for adjustment issues--Even with venting the box can top 100 degrees easily, and plants dry out and overheat rapidly. I water everything thoroughly and keep a close eye the first day out--often leaving plants for just a few hours to adjust. Starting plants out on an cloudy day is a safe bet as well (did you know that an overcast day is still 1000-2000 lumens?) And on gloomy days in the low 30s my greenhouse still hits mid-60 degrees easily.
- Get a remote thermometer. Seriously, these little gadgets have saved me lots of times. I keep the base in a spot I walk by frequently, and a transmitter in the hoop and the cold frame. It helps me gauge when to take things outside, and when to rescue things when the hoop hits 115 degrees and I need to open a vent. Mine can also record highs and lows, which can be helpful when you are getting ready to leave things out overnight. A regular thermometer works fine too, but the remotes are inexpensive and save you a few trips. Bonus: also useful for home-brewing and chicken rearing!
- Ventilation: Our original design used an adjustable prop. Later we added a Univent--another super useful (but kind of pricey) gadget. These have a piston which expands as the temperature rises, lifting the lid. I love mine, and I think it's saved my plants more than a few times. It gives you a little more flexibility as it will close the lid completely in the evenings, if you can't get to it right away.
There are tons of great designs out there and you can even improvise a temporary space with some hay bales, a window, or hardware store plastic. That said, if you don't have the time or inclination to do it yourself, and you are in the Madison area: we are planning on building a few extra models for sale this spring. If you are interested, details are here.