Dormancy Article


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Huntington, WV
I remember reading an article earlier this year that detailed minimum temps required for dormancy for a number of species as well as the number of hours required. Does anyone have the link to this article?
I ask because I have a location under the house that is not heated but due to being under a heated room seldom drops below 35F. I want to use this area for my D Trees but want to make sure their dormancy requirements are met. Any help is appreciated.
thanks for the help but that's not it. That article contains alot of good info but the article I'm trying to find goes into more detail
The short answer for storage under your deck is no. The freeze thaw cycle will do your trees more harm then good and possibly damage the roots.
My philosophy in overwintering hardy trees in cold climates was very simple; 1) Protect the root zone from extreme temp swings by applying mulch (wood chips) over the pot and up to the trunk, and 2) place the trees out of the sun and wind in a location where they will freeze solid and stay that way as late into the spring as possible. I suspect your trees would recieve adequate chilling hours under the porch if the temps there were mostly below 40F for the coldest months of the winter. The main problem I see with the location you mention is less of a freeze-thaw issue and more that I think your trees will likely awake from dormancy too soon, as in March or early April, and you will need to protect them from frost while providing them with adequate light. Good luck,

Rick and Dave, thanks for the help! I was afraid that it would be too warm under there. I have a shed that I kept my trees inmlast winter but I recently put a min max thermo in there and the temps at the coldest parts of the day are actually colder than the ambient temp. Not to mention that it heats considerably on sunny days. I suppose I will just heel and mulch them in. I don't want to keep them in the shed this year as I lost a couple that I kept in there last winter. Thanks for the advice fellas
It is really unnecessary to know the exact number of dormancy hours required for any tree. It is only half the equation for dormancy anyway.

Chilling hours are the number of hours required for a tree to be able to begin growth again--Fulfilling that requirement doesn't mean the tree should actually begin growing. If a tree fulfills its chilling requirement at the end of January, that means it is ready to begin growing again if the ground (soil) temperature allows it. Unlike entering dormancy, exiting dormancy is driven by soil temperatures (once the chilling requirement is met). That means, if you get a warm spell above 35 or 40 degrees for a few days, your tree will begin to grow, which means it will lose ALL of its resistance to winter cold. That's a very very bad thing.

The thing to do is to keep your trees as cold as they can stand it for as long as possible (hopefully past February). Mulching them into a shaded spot in the garden is a start. Eight inches of mulch on top of the pot "lags" air temperatures--allowing as much as 10 or15 degrees difference in warmth or cold.

The issue with putting the trees under your deck would be heat retention--it would provide to warm an amibent temperature to sustain dormancy...
Sorry. New guy jumping in with a question.

If you put mulch over the pot and keep it in a shady spot out of the wind, would you water it. Or, would you let the rain naturally water it?
If it was well watered before heeling it in or appling mulch, you should be ok, but I would still check from time to time.

I have always let the containers freeze a little before heeling in to buffer the plants against temp fluctuations.
If you make sure to keep snow on top of the trees, it will act as a insulator and on the warmer days it will melt some, supplying water.

In Michigan here where we get some serious freeze/thaw cycles, I protect my trees from wind but do not mulch them in. However, I am able to keep them covered with snow most of the winter. I also pack them pretty tightly together on a piece of ground that is higher than the surrounding area, assuring that they are not sitting in water at anytime, even after a thaw. Over the years I have lost just a couple young trees and one of these was a trident which requires more protection here.

One of the most important things to remember in overwintering trees under mulch is to make sure the pot is placed on a solid support on the ground (like bricks, or brick pavers) and there is an air space underneath the pot before piling on the mulch.

That space will insure the pot drains during the winter and doesn't sit in standing water. If you just place the pot on the ground (or worse, in a hole in the ground),the drainage holes will be blocked, or will become blocked as the pot settles in over the coming months. That is a very bad situation, especially in areas that don't get snow, but alot of rain in the winter months.

When I put things into storage (and I store everything in beds outside under mulch)--I make sure the pot is well watered and make sure the mulch is also wet through to the pot. Dry-densely packed mulch on a pot can draw moisture out of the pot, as well as shed rainfall that will keep the plant moist all winter. After that initial watering, I don't water at all during the winter, relying on rainfall and the pots' drainage to take care of things. I've done this for 15 years or so. Have had some issues with some species--chinese elms in particular--but those were mostly temperature-related.
Here in the Southeast we have strange Winter weather. For instance tomorrow the high is 60F, but the low is 25F. I have a shed that I move my trees in and out of (lots of moving) during the winter. even with these flunctuations the trees stay dormant until about mid March. My teacher Warren Hill moves his most valuable and finished bonsai into a shed where they stay the whole winter. It's climate controled to stay around 40F. His big Ponderosas and Pines stay outside on the benches all year.
Thanks for all the help guys.

We're having a crazy cold spell here in Washington this week so I'm kinda nervous. It's getting down into the mid-teens at night. I don't want to put it in the garage. I discovered last year it was too warm in there and the tree started leafing in Feb. So, hopefully with the tips I'm getting here will help.

@bougie nights - What is heeling in?

Thanks again all,


What is heeling in?

Dig a hole deep enough to set your potted tree in to cover the pot, as much as up to the first branch.

Cover the soil with cloth, I like to use old t shirts etc., this will keep most of the "mulch" out of the soil.

Set the pot in the hole, with something under it to keep it off the bottom of the hole ( keeps it from drowning if for some reason you get a lot of water in the pot - there are as many ways as bonsai artists) then cover the pot with mulch, up to grade.

I like to add in, put a wind break around the tree, this can be one of the most effective protection methods there is.

This method works very well, unless you want the tree out early for work, the type of mulch will make it easier or not to lift the tree early. The chunkier the mulch the easier it will be to get it out when the ground is frozen.
Bill can you post some pictures of your system of putting trees to bed for the winter? I want to develop a bed next year. My trees are growing and the greenhouse is getting more crowded than is healthy. We get snow so a good set up would be valuable.

What do you think about a raised bed filled with wood chips?
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"What do you think about a raised bed filled with wood chips?"

Might be OK, depending on species in it and its size--since raised beds are exposed on three sides, they can freeze through in the later months of winter.

A cold pit with mulch is more effective than a raised bed. The ground offers vastly more temperature buffering capabilities than a raised bed. A pit even six inches deep can be effective. A foot deep is better. Backfill with mulch and cover it to prevent excess rain. A drainage gravel layer along with a central drain pipe make things alot easier too.
Thanks Rockm, that makes sense. I have access to large commercial metal door frames (construction rejects). I have built raised beds with them but there is no reason I couldn't dig one in to frame a pit. It would be less conspicuous when not in use in the warmer months too.
Yamadori, what rockm said, mine is made of old storm windows, surrounding a pit approx. 12" deep.
with the bottom made of about 4" of gravel for the "floor". I put the trees in the pit ( pots covered with cloth) then put mulch in, around, and on top of the pots to burry them usually up to the first branch. On top of the window frame box I put a sheet of old 1/2' plywood, with an opaque plastic cover that drapes down over the windows, so sunlight doesn't warm it much, but give some light for those that might need a lumen or three through the warmer days.

The cover is relatively easy to take off, so I can put some snow in every so often to keep them cold, and to provide some water.

Light is probably not needed, but mine allows it, I have some club members that have underground boxes with a lid, thiers works fine as well. Honestly the cold frames are great for hardy, and plants that need a little protection, if you have nothing but plant material hardy to your area, just burry them as above next to your house (flower bed maybe) and that works as well especially if you can set a wind break.
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