I have a few collected trees and after watching the streams, listening to some podcasts, and looking into it further, I feel would benefit from being on a heat mat this winter.
My question is when to put the trees onto the heat?
I have a collected Ponderosa, Virginia pine, Live oak and Virginia juniper. I have an air layered (this season) Swamp oak and Japanese maple that I was planning to put in the heat bed. It’s been unseasonably warm around here, most deciduous are still in green leaf.
What I think I’ve learned so far is that all these trees need the cold for dormancy and that temperatures from 70-80° are optimal for root growth. I’m unsure whether I should wait until we get a few cold spells / frosts to get them going into dormancy before putting them on the heat or to put them on the heat now before the soil temperature drops below 42° and root grow stalls. I did find several threads about heatbeds, heat bed maintenance, transitioning off of heatbeds, and similar and gained a lot from reading them. Clearly this is just me struggling with horticultural concepts and it’s probably obvious…but I figured I’d ask those with experience instead of just going with my gut and messing up. Any help would be much appreciated, thanks in advance.
Ive just set up a mini heatbed for a JBP that i had to emergency repot a week ago in the UK.
The trick is to keep the container soil and root mass at around 80F (26C) for optimum root growth. However it is the difference between ambient temperature and root temperature that will optimise root growth. When the ambient temperature is low (<45F) and the root temperature is at that 80F mark it encourages the tree to put its energy into root growth rather than the foliage. If the ambient temperatures are too hi a heatbed will be less effective as the tree will be allocating energy to both.
That being said a heatbed shouldn’t do any harm (as long as its not too hot!!!) if its not cold enough outside, just won’t have as bigger benefit until ambient temp drops below 45F and the temperature gradient between roots and outside increases.
Hope you have success with it! Its my first go at using a heatbed so i will see if its worked come spring and if the JBP has recovered and grows well!
Hi Josh, I assume you collected them in the spring / early part of the year? Have they grown well or at all since then? You do need to let them go into dormancy before doing anything or risk energy depletion. What does the average winter look like in your area? You could probably get away with simply bringing them into an unheated greenhouse during the winter. While you won’t get a much root growth as a heat bed, you will get some especially if the have contact with the floor.
Sorry to hear about the emergency repot scenario but thanks for clarifying some of those concepts. I was struggling with the idea of the tree going dormant but still dedicating energy to root growth. Your description about ambient temps vs root temps and correspondingly foliar growth vs root growth is helping me connect the dots.
Just a heads up, here in Virginia we had a temperature spike of about 30° Yesterday. While the control was set to 85° F (29°C) which means it’s approximately 75°F (24° C) at the bottom of the bed when the ambient temperature is about 40°F (4°C). The spike in air temperature raised the bottom of the bed temperature drastically. I’ve been checking temps at different levels in the bed with an infrared thermometer so fortunately I was able to back off the temperature before there was a major problem.
So what I’ve learned so far about my set up is on days with drastic temperature swings even though the controller turns off the heat element, the fast rising ambient temps coupled with the heat storage capacity (of my bed material) can raise the temperature at the roots into the danger zone.
Thanks for the advice on temp spikes mate! Sadly (or thankfully in this case) I’m based in the UK so we’re lucky if we get a temperature spike in the middle of summer!
You’re right to be concerned regarding dormancy and active root growth. It’s ok as a one off to help a struggling tree or to help post repot, but you wouldn’t want to overwinter on a heatbed regularly on the same tree as that repeated use of stored resources to build the roots would gradually weaken the tree and could lead to a general decline.
I only built a tiny bed with room for max 2 trees so I’ve actually set the thermostat thermometer in the centre of the soil mass of the tree which may be an idea you could employ if you’ve only got one or two trees in the bed
It might be worth waiting Josh until January in the hope of avoiding too many spikes. The collected trees will be brim full of energy anyway after growing in the ground.
Hey Keith, thanks for commenting and sorry for the delayed response. Two of them were collected this fall. The average winter here is 25-35°F. It may get to 15° at night a few times a year but that’s uncommon and the average midday temp is 35-40°. I agree with you though, for the most part I don’t think I need to do too much for winter protection. Most of the trees are on the ground, grouped up, along a fence wind break.
The part that’s counter intuitive is getting a tree into dormancy all the while promoting root growth. On a conceptual level I grasp the difference between the two types of dormancy but understanding what’s really going on horticulturally is beyond me at this point, but I’ll get there. Also in your subsequent post that’s a great point, about the trees being full of energy from the field. The trees collected most recently had all fall to store energy to aid in winter hardiness. The air layers and the costal oak (poor root mass) are probably the only trees that need or would significantly benefit from the heatmat. Thanks for the guidance.
With your climate a mulched heat bed in the open with the ability to throw a blanket over it on the coldest nights might work well. The roots would be warm, but the tops would see a typical winter.
That describes my set up well. I have some inexpensive tent frame like supports with clear plastic sheet covers that can zip closed if need be.