The Hot Frame ~ My Mini-Greenhouse Build

7 April 2018


My eagerness for spring is prompted by my love of growing things so I feel like a part of my emotional life has been on hold, waiting for winter to pass. I wanted a green house- so badly- but from past experience I know a greenhouse needs daily attention. Once spring (finally) arrives, I'll be half the time here and half the time at the farm until the planting, berry patch tending and "spring chores" are done. I can't be in two places at once- though I would like to.
So a greenhouse was out of the question without help. If I built a greenhouse at the farm, my BFF (best farm friend) Paula offered to tend to it in my stead- but that's asking a lot AND it's colder up there, longer. The water is not even turned on at the farm, and cannot be until it stops freezing at night.
If I built it here in NJ, my sweet Rick offered to tend to it anytime I was at the farm doing the spring set up. In years past, the weather in NJ has provided a two-to-three week head start to planting in difference to the farm. So I was leaning toward a set-up in NJ.

I live in a retirement community with regulations, one of which is that no structures can be built in the yards- so a greenhouse was out. BUT, I have a back patio (pictured above) that gets southern light most of the day which was a perfect  location to build a modified greenhouse- more than a cold frame, less than a hothouse- so I call it a Hot Frame. I designed it to be ergonomically easy on my back, with heat and vents, close to my hose for watering- and of course it had to be budget friendly.

My sketch of the Hot Frame is crude- but this is the idea I worked off of. The size of a hot frame, if you choose to build one, can be anything that fits into your space that gets 6-7 hours of sunshine a day. 
My considerations were:
1) the size of my patio area
2) that I would be storing this at the farm to reuse each year so it had to de-construct minimally- front, back and roof could be left intact-  and fit into my car to transport it  Only the plastic and a few pieces of lathe would have to be replaced each year.
3) light weight, so I used 5/4 x 3.5 spruce as my framing material, figuring a snow load was only a remote possibility at this time of year. 
4) economical so the spruce was purchased in 12' lengths and cut in half to 6' pieces for parts of the build to minimize waste 
5)  was large enough that the smallest readily-available electric heater would not over heat the space 
6) the roof could be opened to load it with growing flats and vent to cool when (if?) the sun comes out.
7) a 2-piece digital thermometer was necessary to monitor temperatures inside the Hot Frame from inside my house.
8) An omission on the sketch is that  1" x 2" rails were added to the inside front and back, 16" from the floor that would later be used to support lathe to make a bench for the growing plants.

I made 2  6' long boxes and screwed them together to form one 12' x 40" Hot Frame.

Some tips to consider:
Use 6 mil plastic to wrap the frame (I wrapped it as one long 12' frame). A roll of 10' x 25' clear (which is not clear, actually) plastic was just enough to cover. Do not attach the roof to the base until both parts  are covered and leave the plastic loose on what will be the hinge side of the roof. Cut the plastic 8-10" wider and longer than your frame so on the top of the frame, it can be rolled to the inside and stapled and have a 4" "skirt" at the bottom. Tap staples with a hammer to make sure they are well set.

 Placing the roof over the frame, match it at the back and check that it is  square to the top of the frame. Screw 2 hinges to attach the roof to the frame. Once the hinges are attached, finish stapling the roof plastic which is stapled to the frame giving a water proof seam between the frame and the roof.

Use lathe (which is so thin now it can be attached with 3/4" staples) to hold the plastic onto the frame. The plastic will rip from the staples from wind blowing if it is not secured on the roof and anywhere you've added staples to the framing.  Use lathe around the bottom perimeter to secure the plastic to the frame ( see the roof and "skirt"  in the main picture)

It's imperative to have (2) folding supports - one on each back corner- to attach the roof to the sides otherwise a gust of wind will rip the roof off (I used 4 because my roof was done in 2 sections). Just FYI, these do come right and left facing (ask me how I learned this tip  LOL)

Gusts of wind can also open the Hot Frame so I used hooks and eyes at the corners to hold the roof down.


I made a door to access the heater without having to open the top. I added a horizontal piece of framing between 2 of the front uprights and cut an opening into the plastic at bottom of the frame, wrapping the cut plastic onto the framing pieces and stapling. I was concerned that rain water run off might get into the heater space, so I stapled an outer piece of plastic to the top of the front frame cut about 3" wider than my opening and about 4" longer than the height.  I secured it with a piece of framing material, as shown above.

6) Inside the little door, the small fan forced heater (safety features and adjustable thermostat- Pelonis HF 1003 from Lowe's) sits on 3 tiles to keep it dry from any water penetration and level. An outdoor extension cord connects to the heater cord.


The cord plugs are water protected in a plastic Glad food storage box which was cut to make room for the cords to fit snuggly into the box.

THE HEATER, CORDS AND TILES WILL BE TAKEN OUT OF THE HOT FRAME WHENEVER THE PLANTS ARE WATERED.  I admit this is not the ideal solution, but the heater will probably be used for just  2-3 weeks so, for me, to have a place to grow plants, this inconvenience is worth it.


Sticky Velcro was added to each side of the little door hatch- on the plastic of the flap and the plastic covering the frame so it is well sealed when closed.

Install the sensor of a  two piece thermometer at the corner farthest from the heater- this will be your coldest spot. The thermometer I used is a wireless Acu-Rite Weather Thermometer (Lowe's). The digital read out is kept in the house and the 2nd piece is a sensor which hangs in the Hot Frame. From a distance of up to 165', you'll know the temperature inside the Hot Frame and can adjust the temperature if necessary. I love the tech!

I ran a very make-shift center support for the potting benches with left over wood 16" high to match the side rails which were added to the inside front and back frames. Lathe strips span the width of the Hot Frame and become a plant table  (some still need to be set in place). It's not necessary to nail or staple the lathe for the plant table.

You can see the digital sensor mounted in the Hot Frame. Before adding plants, I ran the heater for a night and worked out a a few inconsistencies of the heat- there will be a 5-7 degree difference in the floor and ceiling of the Hot Frame. I felt confident enough today to load up some of the seedlings I've started and I'm looking forward to a fun and wonderful growing season.
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