Intermediate results of worm bin temperature testing.

by Bob Shoaf
(Alamogordo, NM USA)

Jan 4, 2012 Worm bin set up and temperature conclusions:

I purchased a 12 foot GRO Quick electric soil heating cable on the Internet. Just google using those words. They are about $30. Their instructions suggested tying the cable to hardware cloth with .5” x .5” grid. I used twine, but I think when I take the cable out I’ll replace the twine with plastic ties similar to ties used to wrap electric cables. The ties will last much longer. The 12 foot cable uses 42 watts, 3.5 watts per foot.

There is a heavy duty soil warming cable that I’ve seen during my searches. It has a 6 inch minimum distance between the cable in the soil. The minimum length I saw was 20 feet. Way to long for my worm bins.

Gardeners use the Gro Quick for warming the soil for seed germination. The heavy duty ones were to warm the soil out in the garden.

I tried to account for as many variables as possible. I did not put worms in my test bin, which was outside on the South side of my shed. I watered the bedding. I haven’t turned it. Turning would be a problem with the hardware cloth in the bin. A big variable that I did not include was food for the worms. Since I didn’t include worms, I didn’t include food. Food can generate some heat which could alter my readings somewhat. But I think if one did have worms in the test bin, if they were feed in the coldest corner of the bin, the temps wouldn’t be any higher than the higher ones on the sun side.

I have about 6 inches of bedding with the hardware cloth about half way down. I took out the necessary bedding, then measured for the size of the hardware cloth.

To determine the length of heating cable, I took a string and string it around the bedding at the depth you want to place the cable. Then ordered that size. The instructions say do not touch or cross the cables. String the cable so the minimum distance between any part of the cable is 3 inches. At the end I had about 6 inches left so I did put a few inches of cable closer than recommended. I strung the 12 foot as close to the 3 inch separation as possible.


Bedding consisted of 45% horse manure and 45% peat moss and 10% coconut coir.

I bought my thermometer at Wal-Mart, $8.00. I purchased one at K-Mart also for $5.00, but it differed by about 5 degrees so did not use it. I would say my readings could vary by 2-3 degrees due to my not being consistent with where I placed the thermometer and how deep I placed it. I’m sure at times the thermometer was closer to the cable than at other times. And I’m sure the distance from the side of the bin would have some effect. I wasn’t real consistent with placement and depth of thermometer. Placement of the thermometer could vary by an inch or so.

Temperatures are fine in the bin if the cable is turned off about 11:00A or 11:30A. Temps in the bin range from 72 to 84 at this time. By 3:00P to 4:00P (usually the warmest part of the day) the temps from sun alone range from low 80’s to about 100. The highest temps are on the South side of the bin which is facing the sun. The worms would have plenty of room to migrate to the cooler areas in the bin. If this higher temp was a concern, one could turn off the heat cable earlier. I may test that also in the future.

At night, with the warming cable on, the temperatures in the bin are generally in the low 60’s when the temps are in the low 20’s, Wind Chill Factor may play a part here too so consider that when temps are low.

I’m going to start looking at when to turn the heat back on as the sun goes down.

I still have quite a bit of testing to do. Temps will probably be in the teens occasionally. I’m interested to see the bin temps then.

Bob

P.S. I have not put any insulation around the bin. I did put a big towel on top to cover the holes in the lid. There are holes on all four sides just below the lid.

Note from Liz:
Thanks so much for this, I know others will benefit from it.
Here is a heating cable like the one Bob is referring to: