Non-electric heat sources under covered tree in spring?

I’m planning on covering a half dozen trees this year to protect the blossoms from frost. Normally people seem to use a 100 watt light bulb under the covering for heat. My trees area about 150’ feet from my house and spread out from each other, so running electric cords will be a bit of a pain. Does anyone have any ideas on other heat sources that could be used. This may sound silly, but what about heating up a large sandstone (larger than a basketball) then wrapping it with reflective bubble insulation. Even when wrapped in insulation, it should still slowly lose heat. I’ve heard soapstone is best for holding heat but I have no idea where to get raw soapstone boulders, but I have lots of large sandstone. Any other ideas?

1 Like

Grandpa use to use what he called smudge pots , basically an oil pot with a lid and a wick . Not sure how safe they would be to use. Fire danger comes to mind

A bucket or two of hot water/tree?

1 Like

Smudge pots are still used here, many are changing to propane orchard heaters when they replant.

1 Like

Nothing beats the heat-holding capacity of water. It has the highest ‘specific heat’ of essentially any material. The classic greenhouse arrangement is water in a flat black, somewhat insulating container. Sun radiation heats it up during the day and it slowly gives off heat during the night. The larger the container, the less insulating the container could (should) be. Of course the tree and container need to be insulated as a unit in a way that sun energy can reach the interior of the enclosure, especially the water container.

1 Like

A side note: Using standard bulbs, lower wattage incandescent bulbs are less efficient light-wise (more efficient heat-wise) than higher wattage bulbs. Example: two 60 Watt bulbs may put out about the same light as one 100 Watt bulb but they might provide three times the heat.


@ztom did you try heated rock or water or anything under your trees last spring? Results? When we clean out hot ashes & coals from our woodstove (which is soapstone and yes it does hold heat well) iput the bucket in the greenhouse and it will still be warm 12 hrs later. But that’s a much milder environment than outside. But hot coals used to be a heat source in olden days. There’s a lot of info on heat storage-release materials in the solar heating area that mjght give some ideas. For next year that is. Intriguing idea for just a few trees. Sue

This doesn’t answer the original question, but I wonder how an electric blanket would work. You would have to keep it dry with a good waterproof covering, of course.

Riding around I sometimes see those big piles of mulch steaming on cold mornings and always thought they could be used as a heat source with pipes pulling warm air from the center. It would probably take a huge pile to do any good.

1 Like

I bought a black 35 gal garbage can placed it next to my satsuma tree filled it with water and capped it with clear greenhouse film. The water gets warm during the day. At night I cover the tree and can with sheets. That gives me 5-10 degrees depending on conditions based on inside vs outside thermometers. For example last week it got down to 24 but was 33 under the cover. Right now it is 31 but 36 under cover. We’ve been in the low 40s for 3 days so the water really cooled off. These are 7’ tall 6 ft diameter trees. You would probably need many cans if trees bigger. Maybe not practical.