Seed Starting Lighted Table


I have a 6x8 foot greenhouse that I use for growing my own bedding plants.  I usually start heating and using it the first weekend in February which is the correct time for an extended season vegetable garden.  I need to start bedding plants for the high tunnel starting in mid December.  December and January are the coldest months and I don’t want to heat my greenhouse those months.  It is less expensive to buy light than it is to buy that much heat so I built this lighted seed starting table to start bedding plants in my home before I start up the greenhouse.  It is a pretty quick project to make.  I started it on a Saturday morning and had flats of seeds planted by the end of the day. 

Here is the list of materials I used:

1 - 2 foot by 4 foot plastic LifeTime table

2 - 4 foot, 2 tube, shop lights

4 - feet of chain to suspend the shop lights

2 - 10 foot lengths of 3/4 inch PVC schedule 40 PVC pipe

4 - 3/4 inch PVC 90 degree elbows

4 - 3/4 inch PVC T’s

4 - 1 1/2 inch long 1/4 inch bolts

4 - 1 1/2 inch long  1/4 inch screws

1 - timer with 2 output plugs

1 - single flat seed starting heat mat

1 - thermostat control for the heat mat

1 - 12 inch by 20 inch closed cell foam insulation board

4 - seed starting flats with drain holes

4 - seed starting flats without drain holes

Here is the list of tools I used:

Portable electric drill with a 3/16 inch drill bit

Screwdrivers of the same type as the bolts and screws purchased

Measuring tape


PVC pipe cutting tool

Rubber Mallet


Build details:

First start by cutting the PVC pipe. There will only be two 9 inch pieces of pipe left at the end of this project so cut carefully or you will be going back for more pipe.  Each length of pipe will be cut exactly the same.  One length will be used to make one half of the light stand and the other piece will be used to make the other half.  Make the following cuts from one length of pipe:

2 - 24 inch lengths - These are the vertical posts on the corners of the table

2 - 3 3/4 inch lengths

1 - 7 7/8 inch length

1 - 48 inch length

Then cut the other length of pipe the same way.

When you look on the underside of the table you will see a groove in the forming of the plastic inside edge of the table.  This is the location to drill the hole to mount the stand uprights.  Measure up from the bottom edge of the table 3/16 inch.  Feel the indentation on the back side of the table edge and align the drill bit to the center of the indentation.  Drill through the table.  Drill holes in the 24 inch pieces of pipe 3/8 and 1 3/8 inches from the end.  I used a 3/16 inch drill bit so I had to screw the bolts through the bottom hole in the pipe and table. Attach the nut on the back side of the bolt and tighten until the pipe starts to elongate. 

Use a level to make sure the pipe is vertical and drill through the upper hole in the pipe through the table.  Install the screw to hold the pipe vertical. 

When you look from the bottom of the table is should look like this.

From the end of the table it should look like this.  

Rather than glueing the PVC pipe and fittings together it looks nicer to put them together with a dry fit.  They won’t slide all the way on without some lubricant.  WD 40 works well for this.  Assemble the top ends by spraying some WD 40 on the inside of the fittings and then tapping them together with a rubber mallet.  Make sure the T’s are 90 degrees offset from the elbows. 

With the top ends assembled lubricate the bottom side of the elbows and attach them to the end uprights.  Be sure to hold the pipes while tapping so that all the force of the tapping is not transfered to the screw and bolt holding them to the table.  Lubricate and install the 48 inches sections of pipe between the two ends.  Your table and light stand should now look like this. 

Your shop lights should have come with 4 S hooks.  Use these to attach the chain to the light.  Loop the chain over the pipe and use an S hook to attach the chain to itself.  This makes it possible to adjust the lights up and down. 

Construction is now completed.  Now it is time to start setting up the timers and heat mat.  Here are the things you will need.  A seed starting heat mat large enough for 1 flat.  A thermostat to control the heat mat.  A timer to automatically turn the lights on and off.  Since we have two lights it should have two outlets on it.  The heat mat will work more efficiently if it is not setting directly on the table surface.  I use a piece of 1/2 thick closed cell foam insulation under the heat mat. 

When growing with a light stand it is important to keep the lights as close as possible to the plants.  Light levels drop drastically the farther the light is from the plants.  I used a foot candle light meter to measure the intensity of the light with the lights adjusted to three heights.  With the lights set two inches above the flats the meter measured 1000 foot candles of light.  With lights set 6 inches above the plants the meter measured 750 foot candles.  With the lights set 12 inches above the plants the meter measured 500 foot candles.  This illustrates how important it is to keep the lights just above the plants for maximum effectivity.  The lights should be on for 16 hours a day.

Cool season plants such as lettuce, spinach, broccoli, onions germinate well with soil temperatures below 70.  Room temperature without a heat mat is sufficient for them.  Warm season plants such as Tomatoes, peppers, squash, melons do much better with a soil temperature around 80 degrees.  You will want a heat mat to help germinate these.