Building a Heated Seed Starts Box

If you are looking for something to spiffy up your greenhouse and liven things up, try using these plans to construct a heated seed box for starting your plants. This box is easy to construct and and with the incredible heated mat that stays at 75 degrees your seeds will jump up in quick fashion.

While all seeds do not like to be transplanted, some are fine with it. Start your seeds in this tray and when they are big enough move them to 4" pots. This design has part of the box not heated for seeds that like it cooler. You can make your's smaller and seed mats come in different sizes.

Seed starts give you a jump on the season and let you grow plants when you would normally just be doing your yearly prep and maintainance.

Materials list:

2 8'x4"x4" pine or treated

2 2' 2"x4" pieces

1 3/4" sheet plywood

4 brackets

2 2"x6"x6' pine or treated

2 3'x5' plastic sheeting

1 1/2" wood screws

Build the Tray:

We cut each 2"x6" board into a two foot and 4 foot piece.We then screwed the edges together as shown. Notice that we put the 2' piece on the inside to insure the inside was 24 inches.We cut the bottom to fit. We left one corner with only one screw in so that we could wedge the bottom on snuggly and then screw it in from the side. Once in we screwed the corner in tight.

Reinforce the bottom:

Uses scrap wood or new if you have it to reinforce the

bottom. We had 1"x2"pieces lying around so we used these. Again, crew them from the side. The gap that is left in the corners (between the plywood and sides) will add stability to the legs.

Secure the Legs

Secure the brackets to the box first using the screws. Next secure the legs. They will be a little unstable and there will be an overhang on the bracket.

See the overhanging bracket?

That's a good thing.

Hammer the bracket around the corner for a snug fit.

See how nicely that fits?

Make sure to screw it off.

Securing the Legs:

Carefully turn over the table, being careful not to jostle the legs. Screw the legs from the top with two or three more screws to give that final stability.

Line the bottom with plastic.

Staple the bottom down.

Insulate and add the mat:

We used a yoga mat--obviously not in use-- for our insulation. We put the heating mat (designed for plant trays) in and then affixed the cord with electrical staples to keep it from moving when we are digging around in the tray. We wanted there to be room at the other end for starts that don't like warmth on their roots.

Finish it up:

Now cover the table with the last piece of plastic. You will be able to wrap it all the way over the edge and under the bottom for a nice clean look. Carefully tack down the plastic on the bottom at the edges with a staple gun, being careful not to puncture the heat mat. Then pull down and over the edge, securing with the staple gun. Now sit back and enjoy your work.