Holiday Lights: Seedling Table

By Gabriel Hahn

The complete but plantless table. Germination and seedling table at back, sowing table at front.

Now that the holidays are past us, lots of people have torn down the Christmas tree lights and taken on the dreaded chore of stuffing them into a tangle and waiting for next year. For those who are sad about taking the lights down, having had the lights up, looking for a better use for them, or turning a consumer product into a producing one, look no further.

You’ve found yet another blog that tells half of someone’s life story before getting to the point. Not really, but our aims are provided, as are instructions, which in words are much more complicated than the building process itself. Read on to learn how to put your lights into a box with a clear lid, making a little greenhouse instead of taking up space in the garage.  

Last February, my friend Andy Gerber and I were in the process of building a greenhouse and would soon need a way to keep our seedlings warm (and cool). We didn’t want to run out and buy a seed mat, propane, or heat the whole greenhouse to keep a few trays of plants warm. Heating air is costly and inefficient. All we needed to keep warm were  the plants, the medium they grow in, and the water that hydrates them. So, we devised a seedling table that would:

-Serve as a potting bench, germination chamber, and growing table at home scale (or larger)  

-Cost little to no money

-Keep seedlings above 50 degrees on the coldest of nights in late February and early March, and cool enough in April and May

-Be low maintenance

 

We wanted to use mostly materials we had on hand. My farmer friend Monica Pless had seen Christmas lights used as a heat source on a table top bench. We had some of those. We also had some plywood, 2x6s, 4x4s, old countertops backed with metal, scrap pieces of rigid foam, and a 4’x6’ sheet of twin wall polycarbonate, often used as greenhouse covering. (Greenhouse or clear plastic can be substituted here, see below for design suggestions) These materials largely dictated our design.

I also purchased an indoor/outdoor thermometer so that I could monitor temperature inside and outside of the seedling/germination section and the greenhouse itself. We vented the chamber manually, but will have automated venting this spring.

Manual venting requires close observation and frequent adjustment. Last year on nights when lows were at 26 F, the inside of the box remained at 80 F while the lights were on. When the sun comes out, things heat up quickly, and must be vented immediately, and the power to the lights switched off. In general, it is best to error on the cool side and act preventatively while keeping in mind quick changes in temperature are more stressful on plants than gradual ones. The insulated feature of this box, especially if inside a greenhouse, is quite protective,adding a buffer of 15 degrees or so at night without the heat of the lights.

The aid of a thermostat to act as a switch for the lights is almost essential for top performing seedlings and germination. It takes the worry out as weather conditions change.

NOTE: The Christmas lights need to be static, preferably rated for indoor and out, and old school ..NOT LEDs. LED bulbs do not produce enough heat! If you don’t have any lights on hand, they can be found in a sale bin, thrift store, or online. We are talking the tiny lights usually seen on a tree. They come in strands of 100-300, about $10 for 100 at this time of year.

For the most part, I encourage people to use what they have on hand. Of course, keep the end goals in mind and adjust where needed to avoid excess troubles. It was nearly a year ago that we built this table, so I wasn’t thinking of documenting the building process at the time, so the photos aren’t glamorous. It was also a large experiment, so we weren’t thinking of how this could be a template for other growers at the time.

That said,  this is an easily replicable model that can be adapted to meet most home grower or small farm needs. Ours was intended to be kept inside of a greenhouse, protected from wind and extreme low temperatures. It could be modified to fit a cold frame, or specifically as an outdoor table, though considerations would need to be made to protect the lid from wind.

 We did most of our seedlings in 10”x20” trays, so we made a large table.

 

Materials: (this list differs a bit from the items shown in the photos to create a better design with less material)

 

  • 4 8’ 2x6s  (sides of table)
  • 4 48”  2x6s  (ends of table)
  • 4 42” 2x4s (legs)
  • 1 45”  2×4  (supports for seeding table)
  • 1 48”  2×4 (support for seeding table)
  • 2 21”  1x4s support for seeding table)
  • 5 51” 1x4s  (supports for seedling/germination chamber. Use 2x4s if adding sand)
  • 1 4×8 sheet of plywood (we used ½”but that’s not vital)
  • 1.5 sheets 4’x8’x1”rigid foam insulation  (material with at least one reflective side preferred but not necessary)
  • 11  ¾”x3/4”x 42” strips (this needn’t be specific, the purpose is for supporting metal above lights and insulation and providing room for sand if used)
  • 2 70” strips of wood, about ¾”on one dimension, with a tapered dimension on the other. 1.5” at on end, 1” at the other to allow for drainage.
  • Twin wall polycarbonate  (or clear greenhouse plastic; but this requires hoops or a supporting frame. 6” concrete mesh would work well)
  • Strands of Xmas (tree) lights (length depends on size of table and how tight the rows are placed)
  • ¼”x25”x48” sheet or corian or other impermeable surface (plywood can also be used here; this is for the seeding table)
  • Caulk
  • Duct tape (to hold light strands in place and seal foam and metal to edge)

Optional but preferred for lower maintenance and optimal environment:  

Tools

  • Saw
  • Drill w bits
  • Impact driver
  • 2 ½” deck screws
  • 2” deck screws
  • J channel  for polycarbonate furring strips)  
  • Measuring tape
  • Square
  • Level
  • Hinges
  • Drywall knife
  • Pencil
  • Sharpie

Basically what is needed is:

A table that can be worked at or above counter height

Enough clearance for plants to grow

A slight slope within the seedling area so that water will drain and not destroy lights

A way to collect and store sunlight

A surface that will allow heat to come through to plants but drain water  

Notes on the building process:

We started with a simple frame, attached legs, then a partition to divide the table into two sections. The short section serves as a sowing table. The other as as seedling/germination table. I like my sowing table to be high, at my lower ribs is ideal so that i can see small seeds easily and reach the back of a 20” tray without bending my back. I’m 5’9” and for me this is at about 42”. Keep in mind that if using trays, the soil level will be 2-3” above the surface of the table, which can affect the comfort zone. The seedling/germination section of the table is lower so that there is space for seedlings to grow and not get burned or hindered by the clear covering. The cross supports for the bottom of this section are set quite deep relative to the top of the table, allowing space for an insulation layer, light strand and sand layer, barrier layer (metal), seedling trays, and growing space for the plants themselves.

Steps:

Assemble table frame. Use screws for all attachments, 2” screws for any joint that involves a 1”piece of lumber.  2 ½” for all others.If using sand, substitute 2x4s for 1x4s on the seedling supports. (leg bracing is optional, not listed in materials section) Check for level at attachment point of legs so that all supports are level. This will matter later when installing barrier above lights.

 

March 15. Morning without the lights turned on.

 

Cut plywood to fit within frame so that it rests on seedling/germination section supports, remembering to notch the corners for the legs. Place in table.

Repeat plywood steps with rigid foam. Hold onto the scrap for insulating the sides and ends later. Caulk around sides, ends and corners. Then tape so that all above the foam is sealed.

Drill hole for light strands through foam and plywood, preferably near an outlet, and away from where you will drain water from the table. A 1 ¼” bit will allow for a plug to fit through.

Lay in and secure tapered 70” pieces along long edges.

Lay ¾” x ¾” supports in about 6” apart, perpendicular to tapered pieces, leaving a couple of inches of space at each end.

Place light strands. Feed a power plug out of the hole, leaving enough wire to connect to an outlet or extension cord. When laying lights, I went side to side on the narrow dimension, about 5” between rows, bending within an inch of the sides with each turn. I laid in enough lights for about half of the 70.5” section of the table, using about 50’ This served as the germination section because of the added bottom heat. The other half of the table received adequate heat because the glazing traps the heat as it rises.

When laying lights, place a spot of tape here and there as you go if needed. If using sand, add now. 1” depth needs about 2.7 cubic feet of sand.

 

Cross section of plywood and insulation layers. The top layer has a reflective surface. The gray is duct tape sealing in the heat.

Lay in metal, (or other heat conductive, fire resistant, solid material) following the steps for the foam and plywood except the hole for the lights.

Drill a ½” hole or two, angled downward out the low end of the table frame where it meets the metal so that water can flow out here. Now caulk and tape all edges and drain spot. of metal to ensure water flows out drain. A bit of standing water is ok.

Cut pieces of remaining foam to cover interior sides of seedling/germination section. I didn’t bother insulating around the legs. Place vertically, with the bottom against the metal and the top flush with the top edge of the table. Secure with screws and washers. Caulk and tape optional.

Trim and lay in corian (or other hard smooth material) for seeding table, making the surface about 1” past the edge of the table. Add plywood beneath the supports if a drawer is desired.

 

The glazing or sheeting can be as simple as laying polycarbonate on top of this section, venting manually when needed. It could be as complicated as placing hinges, weather stripping, a thermostat, and automated vents.. If you know how to do these things, you don’t need this blog post. If you don’t, stay tuned for future posts, or contact me and I can give you the rundown.

 

The only must is that the glazing is longer on each dimension than the inside edge of the seedling/germination section. In an ideal setting, the glazing is tilted toward the south. (this can easily be achieved by cutting the ends of the seedling/germination section at an angle. A 3-6”drop across 48” is sufficient. But know this will come at a loss for head space for plant growth, so adjustments on the other side may be in order.

The pink are scrap insulation used insulate sides. The strips are used to hold the metal above the lights. The exposed screws keep the poly in place when vented.

Keep in mind this is just one design, made entirely from materials on hand. The design could certainly be improved. Things we would change are:

 

Add the thermostat and hinges

Make seedling/germination section deeper, with glazing on top half of the south facing side

Set the glazing at an angle  

Do a better job of sealing the metal layer.

If you or someone you know are interested in designs like these that enable low resource living, becoming more self reliant, or ready to learn or become embedded in permaculture, sign up for our upcoming Permaculture Design Course in Louisville. The PDC is pivotal in connecting to others who are moving toward a more holistic life. The hands-on workshops and classroom experience create an environment and togetherness that simply can’t be had in books or online.