Bottom heat with collected trees

andrewiles

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I'm trying some late summer and fall conifer collecting this year. Subalpine firs and larches. Seems bottom heat is almost universally agreed to be a Good Thing for early spring and fall collecting. But I can't find much more detail than that.

Are there any good resources that list species-specific root growth timeframes and ideal soil temperatures?

With a heat mat I can raise the soil temps 10-15F indefinitely. But it would be nice to understand if there is a target time window to apply the heat, and a sweet spot for the temps.
 

sorce

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I think it's a poor idea.

If we follow what are already established as responsible collecting practices, trees live fine.

So this is in a sense, ignoring responsibility and relying on technology to cater to our greed.

For me, anything unnatural leads to more problems, even if we aren't keen on what those problems are.

Sorce
 

rockm

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Bottom heat is used to get cuttings to root. The collected tree is not really a cutting, but shares some of the same characteristics. "Heat" is a relative thing. Propagators look for soil temps between 70 and 75 F. That's not really "hot." I would be cautious about trying to root collected native trees now, particularly if you have no way to protect the plants in the coming winter...


BTW, bottom heat is hardly "unnatural," for crying out loud. It's one of the things that has been driving tree growth for literally millions of years. Temperate trees don't begin growth in the spring until soil temps around their roots reach above 40. The SUN provides that heat. The plant doesn't care about that. It only cares about the warmth and signal to grow. Using a heat mat to propagate a tree is not "greedy." If you object to this, might as well give up bonsai, since you are similarly artificially exploiting trees' capability to backbud, root and grow in a container. EVERYTHING we do with bonsai is "unnatural" according to your "catering to greed" nonsense. Putting a plant in a container is "greedy" as is forcing it to produce more leaves and branching...
 

bwaynef

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If I were you, I'd protect the rootballs from dipping below about 32-33°F until about January. Then I'd raise the temp for the rootballs to about 40°F, maybe as high as 45°F. While the rootball temp increases, make sure to keep the above-ground portion exposed to cool temps. You want the conditions to be appropriate for the trees to establish roots, but not start pushing top growth that the roots can't sustain. Dormant top, active roots.

While you're at it, make sure the trees are immobilized during this whole process. It doesn't matter what the temps are if the roots aren't stabilized, they'll just break off as they grow (though they're more likely to just not grow).
 

Leo in N E Illinois

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What @bwaynef said. After an initial month or two of roots at just barely above 32 F, for a brief dormancy. Then roots up to 40 to 45 F while keeping branches cool enough to be dormant.

At some point, normal spring temps will wake up trunk and branches. Shoot for about 2 months of roots warm (40 F) and tops dormant. Shorten the cold roots period if your winter is too short. Coastal Washington is quite mild.
 

penumbra

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If I was in zone 8 I wouldn't bother. You're never going to get cold enough to need supplemental heating. I am zone 6 and I don't use bottom heat except for some cutting. Collected trees are simple heeled in mulch or wood chips and that's it.
 

andrewiles

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Thanks everyone. This is helpful. I found a chart earlier, I think here on bonsainut, that shows when certain species tend to grow roots. I know larches were in the list and grew into late fall. But I can't find that thread anymore :(

I can protect them from cold temps this winter. We don't get much below 25F, and only for short periods. From the feedback above it sounds like a good approach could be to turn on bottom heat during any below freezing spells, to keep the roots above freezing, but otherwise leave the tops exposed to the ambient weather to avoid early exit from dormancy. That said, subapline firs and larches are so cold hardy they may not care.

One of the reasons for experimenting with fall collection is that some of our high elevation conifers are really hard to collect in the spring. Too much snow on the ground when they are budding out.
 

JeffS73

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Michael Hagedorn has a chart in Bonsai Heresy with air and ground temps for lots of species. He also did some anecdotal research regarding soil temp under a pot on the ground and temp in a pot (on a bench I think), which would confirm the wisdom of Penumbras method of heeling in.

Anecdotally for me (in a totally different part of the world!) I've had Autumn collected larch survive winter in pots exposed on a wall, whilst Scots and Lodgepole didn't make it. Air temps that year spent a few weeks below 32f / 0c. Last year I collected a Scots pine, and to protect it slipped a heat mat into the tray, and I left it on all winter without a thermostat. We had a couple of bitter weeks below 32f / 0c, and a week below 0c in the middle of Spring. Pots in the greenhouse froze solid. That Pine had a really incredible Spring, pushed great growth considering everything.

I'm in the middle of making a warm bed with thermostat in the greenhouse that will keep temps above 39f /4c. I lost a lot of repotted plants last year. I was probably too eager, but we had some severe cold snaps late on.

After Winter, I was I pleased with how the buds had increased in size, and in fact was just before bud break.

20210512_143418.jpg
 

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