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DIY Heat Mat Speeds Seed Starting

comments (15) December 16th, 2011

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yourownvictorygarden Greg Holdsworth, contributor
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Rope lighting finds new life in a DIY heat mat. Its a great post-holiday project for gardeners.Click To Enlarge

Rope lighting finds new life in a DIY heat mat. It's a great post-holiday project for gardeners.

Photo: Greg Holdsworth (All photos)
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Starting and growing your own transplants from seed is one of the most challenging yet rewarding parts of this gardening passion we all share.

While most veggies will germinate in 'room temperature' without issue, there are cases where some added warmth could benefit the process. First, plants such as peppers, eggplant and tomatoes germinate better in warmer soil (about 70 degrees F is ideal). Second, you may have a situation where the only location you can do your seed starting gets cold in the winter, i.e. a garage or basement. In that case, it's more sensible to only heat the trays rather than the whole room.

The solution? A heat mat. While grow lights placed above the seedlings provide some heat, a heat mat fits the job of warming the soil quite nicely. The problem? Heat mats can be pricey.

While I already own two mats myself, I started to see the need for a third one this winter. Some research online led me to cases where folks had strung holiday lights around young trees or perennials to help protect them from frost damage.


Recycle your rope lighting into an inexpensive heat mat

Since the holidays are upon us, lights of all sizes, colors and shapes stock the shelves of the seasonal departments of most stores. What a bright idea (pun intended) it would be to construct a DIY heat mat using lights?

The heat 'mat' I've built here easily accommodates two of the 1020-standard 11" x 21" seed trays or flats. Rope lights come in a variety of lengths and colors, so you can customize them to fit your specific needs. You'll need the incandescent type of lights, not LEDs. The really cool part? I managed to built this one for about $16. In fact, you may already have the needed materials on hand.

  DIY Heat Mat
Photo A

DIY Heat Mat
Photo B

DIY Heat Mat
Photo C

DIY Heat Mat
Photo D

DIY Heat Mat
Photo E

DIY Heat Mat
Photo F
 
DIY Trellis
  Photo G
 
DIY Heat Mat
  Photo H

In building the mat, the rope light weaves around long thin strips of wood, and both are attached to a 'plank' of plywood. The gaps between the wood strips serve to help with airflow. The rope light will only emit a certain amount of heat – not enough to burn the wood. Since it's thinner than the wood strips, the rope light doesn't come in contact with the seed trays. Since the rope light is insulated for outdoor use, it's protected from water.


What you'll need:

1. Plywood 'plank' (I used a 1-inch thick x 12-inch wide x 4-foot long piece)

2. Two 1" x 2" x 8-foot wood furring strips

3. Wood screws - two packs each of #6 x 1-1/2" and #8 x 3/4" sizes

4. Plastic cable clamps - two packs of 1/2" size

5. Hand saw or jigsaw

6. Tape measure and/or square

7. Pencil

8. Sandpaper

9. Rope light - incandescent type (not LED). I used an 18-foot length.


Skill Level:

Easy to intermediate, depending on your wood-working/cutting skills.


Construction:

1. To correctly wrap the 18-foot rope light as I wanted, I ended up having to cut the 4-foot plank of plywood to approximately 44 -1/2" long, but you can certainly leave the excess on if you don't want to cut it.

2. Cut the two 1" x 2" x 8' furring strips to get four 40" long pieces. Sand any rough edges or surfaces (Photo A).

3. Using the 1-1/2" wood screws, attach the 4 furring strips to the plywood plank (Photo B).

4. Unwind and straighten the rope light (Photo C).

5. Place the closed end of the rope light at the bottom right corner of the plywood plank (if you have the long side facing you). Wrap the rope light around the 5 spaces between the furring strips (the two outside edges are two of them) (Photo D). This is only for rough placement - we'll tighten it down in the next step.

6. Using the plastic cable clamps and the 3/4" wood screws, attach the rope light to the plywood plank (Photo E). I ended up using five clamps along each run of the board, and put an extra one at the ends of the cable to secure it better (Photo F).

7. Light 'em up baby! I mean,... um... plug it in (Photo G).

Your lighted heater is ready for seed-starting duty (Photo H).

So, if you're crafty and are out shopping, why not grab some lights to warm your seeds?


How well does it work?

The heat mat takes approximately 30-45 minutes to fully heat up, and using my hand, felt as warm as the commercial heat mat. Upon taking measurements with both regular and soil thermometers, the numbers were impressive.

Commercial heat mat
Surface temperature
(thermometer placed on top of soil): 73-75 degrees F
Soil temperature: 80-82
Bottom temperature (gap between heat mat and seed trays): 100-102

DIY light heat mat
Surface temperature: 72-74
Soil temperature: 78-80
Bottom temperature: 105-110

Note: To control heating times, use a thermostat or timer.

 
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posted in: seeds, Projects, seed-starting
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Comments (15)

WalrusBoy writes: I built something similar two seasons back it it works really well. The tomatoes love it - I usually have them sprouting in four or five days (most of them are up now and they were seeded last Sunday - six days ago!).

Incandescent elements work the best and they typically have a higher wattage output(about 1.8 or 1.9 Watts/foot so a 12 foot "rope" gives off about 20W of heat). The LED type has a lower output - about 0.75 W/ft - so not as much heat is produced.

I know the ropes are outdoor rated/certified so are OK to have water dripping on them (plus the ends/connectors are sealed when you "slice" them together) but, being an anal engineer type, I wanted something to dissipate the heat produced, so I bought a sheet of heating duct (2'w x 3' long) and screwed that to the top of the furring strips - I though it would keep the heat evenly spread out. seems to do the trick!
Posted: 1:49 pm on March 16th
illuminate1 writes: I want to say thank you for this tutorial! I built this mat myself, the Home Depot cut all the wood to size for me, I just needed a drill to complete. My seeds are germinating at a great rate!
Posted: 8:41 pm on March 8th
prairiechuck writes: Great idea! I found some lights at the local garden store, but the package said "Stays cool to the touch" They weren't LED lights but if they are "cool to the touch" will they still work?
Posted: 1:22 pm on March 1st
PaulsGarden writes: Would it make any difference if the lights were in colored ropes as opposed to clear ones?
Posted: 11:02 pm on February 1st
Ozarkgranny writes: What wattage are your stands of light?
Posted: 7:55 pm on January 31st
arddwr writes: Greg,

Another really great idea! I built the diy heating mat earlier this evening in my garage. It took me about 45 minutes to build the entire mat, from start to finish. It looks great, and I will start my seeds this weekend, and keep a record of how well they do.

I also followed another of your plans and built the PVC pipe grow light setup. That was super simple, and a whole lot easier than some other designs I was thinking about using.

I wish I could post a picture of them here in the comments section.

All in all, I spent about $60 total on all the supplies that I needed to put these two projects together. So, as I calculate it, that's about a $200 savings from what I would have spent on a heating mat, and light system that would cover two flats of seedlings.

Greg, thanks for the great ideas. I've used several of them in my garden, and at one time, I had even considered posting an article on how to build a compost sifter, and about a week before I was going to post, BAM, there your post was! Awesome! Keep the good ideas coming, as I seem to find a place in my garden for most of them.

Next I'm building the raised bed seat that you posted a while back!

Happy Gardening! I'm so looking forward to this growing season!
Posted: 10:39 pm on January 19th
windhovr writes: Great post. I just posted a link to your article on bread baking sites. This mat would serve as a perfect heat source in homemade proofing boxes!
Posted: 11:52 am on January 4th
Marc_Green writes: This is a very practical solution to early seed starting, or even winter growing. The difficulty in this every-growing energy efficient day (which is a good thing!) is that the incandescent fixtures are increasingly hard to find. If you already have them, then you're in luck, but everything in the stores now is all LCD, which produces little heat (verging on none).

We did a similar process with our tunnel cloches last year, using old style christmas lights inside to keep things warm and growing. It gave us food deep into the winter, but of course, once the really deep freeze came, accessing the food inside the cloches because increasingly difficult.

For photos, try this facebook link to our page:
https://www.facebook.com/media/set/?set=a.10150096942907079.301795.278221282078&type=1

You may have to "like" us first on Facebook.
Posted: 11:58 am on January 2nd
erikspring writes: Do you think I could use standard white incandescent holiday light strings (the ones with the small bulbs)? I have a few of those lying around.
Posted: 11:41 pm on December 25th
thebrez1 writes: What a great, yet simple solution. I was asking how you cycled the lights for the heat mat replacement. I am assuming that the 12 hour cycle you refered to was the grow lights. Do you just leave the rope lights on all the time to maintain a steady temp?
Posted: 8:43 pm on December 21st
yourownvictorygarden writes: @jwr12: Good question. If the rope light and commercial heat mat you had provided a watt rating, that would give you some idea. Since you typically have the mats on for a long period of time, I suppose you would have to have a device connected to that outlet that could measure the wattage output. I've just started using this, so time will provide a better idea.

@radevers: Regarding bugs, I don't think it would attract bugs any more or less than grow lights would. I would have to see if the type of light the rope emits is as attractive to light-loving bugs as, let's say, your porch light. Regarding safety, the rope is rated for indoor use as well as outdoor. The heat/light energy given off of the rope simply isn't enough to burn. You would obviously not want the plug to be in an area that could be wet.

@lonejack: I would say you could try it as a light source, but I don't think it would be as powerful as a grow light would. And, like you said, the layers would have to be very close to the seedlings to effectively give them enough light to not make them 'leggy'.

@thebrez1: The temperature of the room this is in is between 66-70 degrees. It would probably have to work harder if it was in a colder room or garage; for example, but I still think it would provide a boost of heat right at the soil where the seeds are germinating... which is the goal. I did not cover the trays and typically don't, due to damping off issues that I had in the past. I have the lights on a timer that turns them on for 12 hours a day, which is a recommended amount.
Posted: 2:59 pm on December 21st
thebrez1 writes: I was wondering how cold the room was where these temp readings were taken? My garage gets pretty cold. And did you cover the trays while the light was on? How long or what cycle did you use for the lights? on all day and off at night/ On for only a couple of hours and if so, at night or during the day? Input...I need Input :)
Posted: 12:38 pm on December 21st
lonejack writes: I wonder if you could use the rope lite for a light source.
By using clear Plexiglas to lay out the lites, I could use the rope lite for heat for the top layer and provide light for a layer below.
The layers would have to be pretty close together.
Thanks for the idea
Posted: 10:57 am on December 21st
radevers writes: Good idea, Greg. I had the same question as jwr12. You could comnpare the label on the commercial heat mat (watts) to the label on the light rope to compare the energy consumption when either one is "ON". But I think some of the heat mats have a thermostat that turn them off at some temperature and back on at some lower temp, so the labeled wattage is used for only a part of the time it is actually plugged in while the lights would use the labeled wattage for all of the time they are plugged in. I also wondered if the lights would attract bugs; have you noticed any bug problem? At first, I thought there might be a safety issue, but if the light rope is rated for outdoor use, it should be OK around the plants/seed trays.
Posted: 9:54 am on December 21st
jwr12 writes: Very interesting! Do you have any sense of how much energy the two kinds of mats use, comparatively? Which one burns watts faster?

Thanks!


Posted: 8:32 am on December 21st
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