I noticed that my wood chip compost pile that I never turned has ice still about 1" below the surface, so that got me to wonder if wood chips are better cold insulators than heat insulators.

  • 1
    The insulating properties of woodchips are irrelevant. What you have, apparently, is woodchips embedded in a block of ice. That is something completely different! To thaw 1 gallon of ice takes about the same amount of heat as to warm 4 gallons of water from freezing up to 70F.
    – alephzero
    Commented Apr 20, 2019 at 17:31
  • 4
    Like a thermos bottle ; the wood chips don't know if the are keeping something hot or cold. Commented May 23, 2019 at 0:53

3 Answers 3


Anything which absorbs water becomes less inaulating. Here is an example: http://www.city-data.com/forum/house/717131-foam-insulation-installed-wet-wood.html The hot summer desiccates the woodchips. Water is taken-over by air that fills the pores. Air is a better insulator. It is very important, however, that a dry summer should help the chips to dry faster than a moist one. In addition, hot air rises. The hot woodchips should lose heat by convection faster than cold chips getting a warm-up. The cold air does not rise and remains above the wood chips for longer.

  • will this bother thawing of the soil if the area was covered since last summer? Commented Apr 19, 2019 at 21:35
  • Mulch is an extra-layer, so basically will delay heat exchange between soil and the air. It is simply less prone to temperature fluctuations. Average temperatures will simply lag behind seasonal changes while keeping same average. The mulch decays more quickly in the summer, and is vital to the nutrients cycle. I advise you to keep mulching anyway. Commented Apr 20, 2019 at 16:29
  • the mulching is to kill off grass, and get a nice area to walk as it's always warmer in that area than the surrounding ground once things warm up Commented Apr 20, 2019 at 21:21

You can get an awful lot of heat out of compost heaps, the bigger the better, we used to heat an entire garden centre, 7 smaller business's and a busy cafe + 2 sets of offices with the heat given off by several hundred tons of mostly grass cuttings but with plenty of general gardening waste, even at edges, it would get so hot that Wellington boots just melted away. Piles turned with an old Ferguson tractor with front end loader, it ate the kleats off the tires

We bought a big load of scrap steel pipe and fittings for a few hundred pounds, a high temperature pump for a bit more, and employed a plumber for a week in the winter. It worked so well, none of the old systems ever came on automatically so every now and then, they had to be turned on by hand.. Saved lots of money back then(1990's) now, with the price of energy for business, we would be saving probably well over £150-200.000 per year.


The composting process creates heat if it is done properly. It can create a lot of heat, like over 150 Fahrenheit (65 celsius).

For composting you need:

  • a mix of nitrogen sources and carbon sources, chopped into small chunks
  • a healthy mix of microbial (micro digesters) and insect/bugs (macro digesters) - generally these will show up with dirt as long as you have throw in some handfuls of local soil and you use some natural materials like leaves (which have bugs on them)
  • mixed thoroughly - like, really really thoroughly
  • and moist - enough that if you pick up a handful and squeeze it then a little bit of water might drip out or be visible on your hand afterward
  • oxygen, from weekly mixing or just a pile design that provides aeration
  • depending on your environment you might want some walls to help keep in moisture (in a dessert) or a roof (to prevent steady rain from soaking the pile) or some insulation like an enclosed box or old scrap of rug or black plastic tarp to help it heat up.

If you did all that in a way that's appropriate for your environment, then the middle of the pile should start heating up within a day. It should get above 100 degrees Fahrenheit (30 celsius) within a week. The outsides of the pile might not ever get warm, which is why you need to mix the whole pile periodically to let the outsides get mixed into the middle.

If your pile is literally frozen in the middle then some key condition is missing and you can start over trying to build the pile and paying more attention to all the details to figure out what was missing.

  • the middle is soft, there is about a 1' hard shell still on it from the hard winter Commented Apr 23, 2019 at 3:40

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