Soil warming newly repotted trees

Lars Grimm

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Does anyone have any experience using soil warming cables or matts to facilitate root growth in newly repotted trees? I have some newly repotted coastal redwoods that came out of very dense clay soil and don't have the best root mass. I was debating trying to let them sit on a heating matt to help facilitate root growth. These trees would be sitting outdoors, but I thought about putting some gravel in a cement mixing tub, laying down a heating element and then placing the tree on top.

Lars
 

Dav4

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Does anyone have any experience using soil warming cables or matts to facilitate root growth in newly repotted trees? I have some newly repotted coastal redwoods that came out of very dense clay soil and don't have the best root mass. I was debating trying to let them sit on a heating matt to help facilitate root growth. These trees would be sitting outdoors, but I thought about putting some gravel in a cement mixing tub, laying down a heating element and then placing the tree on top.

Lars
I've never personally done it, but I do know that Tony Tickle, over in the UK, uses a heated grow bed for his recently collected yamadori and believes it does improve survival.
 

arcina

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Does anyone have any experience using soil warming cables or matts to facilitate root growth in newly repotted trees? I have some newly repotted coastal redwoods that came out of very dense clay soil and don't have the best root mass. I was debating trying to let them sit on a heating matt to help facilitate root growth. These trees would be sitting outdoors, but I thought about putting some gravel in a cement mixing tub, laying down a heating element and then placing the tree on top.

Lars
I have used heating cables with a thermostat for the last 7 years and they work. I mostly use it for collected trees but I also use them for early repotted trees. If you want to start the roots to grow, you need to keep them an around 45F. I have experimented with and without and I have seen better recovery in the heated bed.
 

Lars Grimm

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Alright, here we go. Here are all my components assembled: concrete mixing tub, wire mesh, soil heating coils, and zip ties.
IMG_5889.JPG

I drilled a bunch of holes in the mixing tub to allow drainage.
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Then, I loosely zip tied the heating cable to the metal mesh. The heating element is 12' long and is supposed to warm 3 square feet. The mixing tub is 2 feet x 1.5 feet, so perfect size.
IMG_5891.JPG

I then added a 1.5" layer of pumice to the tub. It is lighter and will still retain moisture. I laid the mesh and heating element in place.
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I then added another 2.5" of pumice in place.
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After about an hour, the air temperature was 50 degrees and the surface temperature was 55 degrees. About 1" above the heating element it was 65 degrees so I removed some pumice and nestled my boxed tree. I filled up the sides with more pumice so it is sitting about an inch deep.
IMG_5900.JPG

The tree is a coastal redwood that i just repotted. It was in heavy clay soil and got beat up a bit during transit so it was relatively weak. During repotting, it didn't have a very large root mass so I really want to give it as much help as possible.

The nice thing about this setup is that it is modular and not too heavy. If the air temperature gets down to just about freezing, I can leave this tree outside. If it gets into the 20s, I can just slide it into the shed where it never gets below freezing.
 

JudyB

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There are also propagation mats you can just sit the container on as well. The only thing I don’t like about these types of cables is that you can’t control the temp on them. The heat mats you can put a controller with a probe in line and actually determine what temp you want. I use them for winter storage as well as for ailing trees or newly repotted sometimes.
 

Lars Grimm

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There are also propagation mats you can just sit the container on as well. The only thing I don’t like about these types of cables is that you can’t control the temp on them. The heat mats you can put a controller with a probe in line and actually determine what temp you want. I use them for winter storage as well as for ailing trees or newly repotted sometimes.
Thanks Judy. I looked at the mats, but it seemed like many of them don't play nice with overly wet conditions. This setup only cost me about $20. If I like it, then I might install a permanent heating bed with thermostat and winter covering. Mirai has a nice video about this.
 

RJG2

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There are also propagation mats you can just sit the container on as well. The only thing I don’t like about these types of cables is that you can’t control the temp on them. The heat mats you can put a controller with a probe in line and actually determine what temp you want. I use them for winter storage as well as for ailing trees or newly repotted sometimes.
I see some thermostats on Amazon that would work for this setup. Just need to make sure the probes are truly waterproof (I see a couple at first glance).

I have a heating mat with probe and the instructions said not to submerge.
 

Lars Grimm

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I see some thermostats on Amazon that would work for this setup. Just need to make sure the probes are truly waterproof (I see a couple at first glance).

I have a heating mat with probe and the instructions said not to submerge.
Do you put your pots directly on the heating mat?
 

Lars Grimm

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There are also propagation mats you can just sit the container on as well. The only thing I don’t like about these types of cables is that you can’t control the temp on them. The heat mats you can put a controller with a probe in line and actually determine what temp you want. I use them for winter storage as well as for ailing trees or newly repotted sometimes.
Judy, if you have a moment, could you share any photographs of your setup? I've long admired your garden design and organization.
 

Bonsai Nut

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roots grow from say 4C/39f upwards. Anything you can do to assist the roots while the canopy is dormant should help 🤷‍♀️

Generally roots grow most in late spring to early summer, followed by a second slight push of growth (depending on species and location) in the fall. This is to a great extent triggered by earlier foliage growth, and elevated auxin levels and sugars provided by the foliage. Though yes, in an absolute sense, cold temps prohibit root growth, and you might want to protect tender roots if you fear that container soil might freeze, I haven't read anything that suggests that heating soil in the winter stimulates root growth - in any substantial way versus extremely low off-season growth. After all where are the roots getting their hormones and energy from since the foliage and vascular system is dormant?

If you want to put the entire tree in a greenhouse or cold frame setting, so that the entire trees wakes up earlier, and starts to push spring growth earlier, then I think you might see results. But putting a dormant tree on a seedling mat? I'm not so sure.
 

Bnana

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In nature you see that vegetation starts to grow earlier in soils that warm up easily and later in very cold wet soils.
That's why farmers like to have their soils not too wet in spring, the grass grows earlier and faster that way.
So temperature of the roots can limit plant growth but I do think the effects of a greenhouse or cold frame will be much bigger.
 

JudyB

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JudyB

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JudyB

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Generally roots grow most in late spring to early summer, followed by a second slight push of growth (depending on species and location) in the fall. This is to a great extent triggered by earlier foliage growth, and elevated auxin levels and sugars provided by the foliage. Though yes, in an absolute sense, cold temps prohibit root growth, and you might want to protect tender roots if you fear that container soil might freeze, I haven't read anything that suggests that heating soil in the winter stimulates root growth - in any substantial way versus extremely low off-season growth. After all where are the roots getting their hormones and energy from since the foliage and vascular system is dormant?

If you want to put the entire tree in a greenhouse or cold frame setting, so that the entire trees wakes up earlier, and starts to push spring growth earlier, then I think you might see results. But putting a dormant tree on a seedling mat? I'm not so sure.
It may be my whole setup that encourages it, but I do see root growth in the winter. I keep the root temps (with heat mats) at about 36, and the air temp no lower than 32.
 

Lars Grimm

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Thanks Judy. Are those blue mats the heating mats? I've looked at some of these pictures before but didn't realize what they were. Do you find the trees dry out faster also?
 

JudyB

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Thanks Judy. Are those blue mats the heating mats? I've looked at some of these pictures before but didn't realize what they were. Do you find the trees dry out faster also?
Yes they are. I water inside that structure about once every week or two. I keep the air fairly humid in there, I set the humidifier for 70%, so the air doesn't dry out the small twigs from the air heater. As far as more often, I suspect so, but I've always been in a structure for overwinter, so don't have a lot to compare to. It does depend on how cold it is outside, as the more the heater comes on, and the more the mats come on then they do dry out faster. But I've never had to worry about it if we went away for a couple weeks in winter.
Also know that both ends of the greenhouse that are glass doors, get pull down blackout shades in the winter, to keep the light level very low in there. The solexx does allow a little light in, but those sides are east and west, so not too bad.

https://www.greenhousemegastore.com/supplies/seed-starting/heat-mats-cables/redi-heat-hd-mats?returnurl=/supplies/seed-starting/heat-mats-cables/
 

JonW

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I've read that roots will grow in the winter so long as temps are around 40 degrees F. Too much warmer and the tree might start growing leaves (coming out of dormancy). There is a bonsai Mirai episode in which he talks about using heating mats with large size Kanuma (I believe it was Kanuma), which holds in and diffuses the heat from the mat so the heat doesn't just rise into the air and heat the room/air.

Even with cuttings, bottom heat seems very important. If I can keep the soil in the 70s, I get better success. I put cuttings on my furnace in the fall and I don't use any supplemental light until I see leaves or am confident the cutting rooted. This has worked really well. Conversely, if you give the cuttings light but not bottom heat, I've seen leaves start to growth without any roots, which of course uses all the resources in the cutting and it dies.

I overwinter a lot of my trees under storm doors. It stays between 35 and 50 degrees. I tried fall repotting on a lot of trees and can tell at least some of them have grown some decent roots. I think it'd be too cold in my climate to do fall repotting and keep my plants outdoors even with some protection like mulch, but I could be wrong.
 
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