DIY Heated Propagation Bench

Sometimes seeds need a little help to get started, and a heated propagation bench can help seeds germinate when temperatures are still on the cold side. The ideal temperature for seed germination depends on what plant you are trying to grow, but most like warm soil to get them off to a good start. A few pieces of wood, screws, a soil warming cable, access to power, and some same is all you need to make your own.

Making a heated propagation bench is relatively simple, and I chose to place my heated propagation bed on the greenhouse staging; here’s how I made mine

Equipment needed to make the bench.

  • Wood, cut to length for your chosen location
  • Eight screws
  • Builders sand
  • Tray big enough to cover your chosen location
  • Soil warming cable
  • Power supply to your chosen location

Step 1 – create the frame to hold the sand

The heated propagation bed will be filled with sand on which seed trays will stand, so the first stage will be to make the frame to hold the sand in. I cut the wood to fit within the tray and checked the fit before drilling pilot holes for the screws. Once the pilot holes were drilled, I screwed the wood together. If I were to do this again, I would countersink the screws to make a cleaner edge.

At this stage, drill a hole around 2 inches from the top big enough for your soil warming cable to pass through and in a location where you want the cable to enter the propagation bench. I chose to place the hole for my soil warming cable at one end close to where I have power in my greenhouse. Test the hole before moving onto the next stage to make sure the cable passes through easily.

Once the wood was screwed together, I placed the tray in the desired location and inserted the wood. The propagation bed will get heavy, so it’s worth getting everything in place now

Step 2 – Part fill with sand

Now it’s time to part fill the warming table with sand. Fill it to the hole you drilled for your soil warming cable. Don’t fill past this hole as you will need to use it in the next stage. Try to make sure the sand is evenly spread so when you layout your soil warming cable, there will be an equal spread of heat.

Step 3 – Lay out the soil warming cable

The soil warming cable is the critical component of this build. It will warm the sand around it, passing the heat up to the surface and into the soil in your seed trays. Spreading the soil warming cable equally through the sand will help get an even spread of warmth across the propagation bench and help you manage the temperature.

You will need to refer to manufacture guidance on how best to spread the cable out, but I chose to run it up and down the bed with equal spacing between runs. It is worth mentioning, and depending on your soil warming cable, a little warmth helps the cable bend and shape. I turned mine on, and after a few minutes, I was able to shape it.

Step 4 – Cover the soil warming cable and plug it in

With the soil warming cable in place, its time to cover it. Fill propagation bench to the top with sand and level it off.

Now the sand in is, it’s time to plug the soil warming cable in and wait for the bench to warm.

Optional step 5 – Control the temperature

Adding a thermostat will give you control over the temperature of the soil. Without one, the soil warming cable will be on all of the time. Different seeds prefer different temperatures to germinate, so having a thermostat will optimise the temperature for the seeds you are trying to grow.

There are different types of thermostats available. There are ones designed for propagation benches and push into the sand, and the soil warming cable plugs into it. You can pick up a generic thermostat with a probe that will allow you to either take your temperature reading in the sand or the soil you are looking to warm.

I picked up a generic thermostat with a probe and planned to control the temperature using different approaches to see what works for me.

With the propagation bench all done, you can start sowing seeds and getting them off to a good start, even when it is cold. Be sure to keep on top of watering as the added heat can dry the soil out quickly.

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