Warm Propagation Box With Christmas Lights

We had a problem starting seeds in our basement during the cold months of January through March. Pepper plants are especially difficult to start if the soil temperature is less than 80-85 degrees. We tried a number of solutions to increase the basement temperature including using a gentle fan to keep warm air from the furnace from escaping.

In 2005 we decided to try to solve the problem a little more formally. We needed a solution that would work to start a few hundred plants at a time, would cost very little, would use very little energy, and would be easy to construct and use. Here is a picture of what we came up with:

We had on hand some 4’x 8’ styrofoam panels (we bought a pallet load from a home improvement store for $10) and cut them down to make a 4’x6’x8" box with a bottom and taped everything together with duct tape. We sealed the joints with foam sealant. The top is just a piece of foam that sits in place.

For heat we used 2 strings of Christmas tree lights lying loosely on the floor of the box.. This is sufficient to raise the temperature 15-20 degrees from the 60 degrees measured on the basement floor. Total cost of the project was about $5. If you had to buy all the materials, the cost would likely be around $30.

The estimated cost to run the system (about 240 watts of power) is around $.60 a day. We can fit about 10 trays of cell packs into the box and a 5-day stay until germanation would cost about $.30 per tray or .004 per plant.

We had a similar, but slightly larger, box outside on our driveway and used it for seedlings. This box was made from 2" foam with a much higher r-value. In addition to a lid we covered the entire unit with plastic to increase the insulation. Two strings of Christmas lights rasied the temperature about 50 degrees from the ambiant air temperature -- 32 degrees outside and 72 degrees inside! During the day we removed the foam lid but left the plastic on. The problem with this design for seedlings was the small amount of air in the box would heat up very rapidly when the sun came out and could cook the plants if we didn’t get the plastic off in time.