Winter Hardening?

[james]

All,

I live in zone 4b.

I keep my bonsai in a heated poly tunnel during the winter, and the trees have done quite well, min temps kept in the 40s. About this time, I put the trees down for the winter in the poly tunnel, yet I find that the deciduous trees have not all dropped their leaves.

I would like to consider leaving them out longer, so they drop their leaves (cuts down on the mess), and I could give them a dormant spray. At this time of year, night time lows are bouncing around, but may go below 30, with a hard freeze.

I think the evergreens will be fine. But am I taking a risk with the deciduous trees? I have japanese maple, tridents, chinese elm (I worry about these the most), hornbeam, beech, crabs, plum, hawthorne. Is it silly to try to harden these trees, just to cut down on greenhouse mess and dormant spray?

Thanks, Josh

 

[davetree]

You can leave your trees out longer. I am in a similar climate and I don't put my trees away until Thanksgiving. It's good to let them freeze a few times before winter, just avoid really cold temps like the teens with a wind. You can winter your trees at 25-35 degrees, 40's is too warm and can give you some trouble with early budding. I don't think some trees go fully dormant with temps in the 40's.

 

[james]

Thanks for the reassurance. Do you concern yourself with letting your trees freeze thaw repeatedly as you suggest with min temps of 25-35? I do get early spring budding, I just run with it and get started earlier in the year.

Thanks

 

[davetree]

I think the bigger issue with your temps in the 40's is not the early budding but the fact that some trees may not go fully dormant. This is stressful for the tree and weakens it over time, and can apparently kill it.

No I am not concerned with freeze thaw. I havent lost a tree to it yet. My trees thaw or freeze very slowly in my storage area. I also insulate them with snow to keep temps more constant if I anticipate temperature swings.

 

[small trees]

I don't think some trees go fully dormant with temps in the 40's.

You must not have ever visited georgia!

 

[james]

DaveTree,

Your experience is valuable to me. I would agree that the trees may not go fully dormant, as my chinese elm can hold its leaves for months after I put away for winter. You reinforce my thought that a couple freezes and a bit cooler poly tunnel may be a reasonable.

Thanks

PS I haven't been to Georgia, but might like to some day

 

[Vance Wood]

If you live in an environment that tends to have really cold snaps, approaching single didgets and even in the early part of the year it is vital that the trees achieve full dormancy and be placed into an area where a freak warm spell is not likely to wake the tree up. If the tree is not fully dormant and February comes along with a few days of warm weather followed by March with near Zero plunges your trees are likely to wake up and the subsequent hard cold can be the end of them. If you have allowed them to become fully dormant and sheltered them from the sun's exposure early in the year, which stimulates them to warm up, and the sap to rise too early you should be OK. A lot of people make the mistake of thinking that you have to prevent a bonsai's roots from freezing and you have to keep the tree warm. The dirty little secret is that you have to keep the trees dormant till at least the last of April, and then that may not be long enough in some climates.

 

[rockm]

"Do you concern yourself with letting your trees freeze thaw repeatedly as you suggest with min temps of 25-35?"

This is not a concern but is DESIREABLE in setting your trees up for dormany when the worst of winter comes. Shallow freezes and thawing in late fall and early winter in which temps don't get much below 20 or so can aide in pushing the tree into dormancy. With no frost or freeze exposure and placement in a heated poly tunnel, I'm surprised you haven't lost any trees yet to early bud break.

I typically leave ALL my trees out, including marginal southern species lke bald cypress and live oak exposed on the benches with no protection until the end of November and even into December depending on the number of hard freezes we get here in No. Va. I want my trees to get hit four or even five times by temps that flirt with the low to mid twenties. Typically trees don't need any protection until temps fall below 15 F or so (depending on species). Allowing them to be exposed to temps as low as 20 F before storage kicks in their cold hardiness mechanisms. Not allowing them to experience those temps won't adequately "harden" them to the coming winter and will require you to go to sometimes ridiculous lengths to avoid prolonged cold.

If you haven't read it yet, here's one of the best articles on overwintering temperate zone bonsai--
http://www.evergreengardenworks.com/overwint.htm
.

 

[james]

Thank you all for the winter hardening advice.

A related question for those of you who allow freezing, what effect do you see on akadama? This is my first year using akadama, and it may break down more quickly with freezing?

 

[Vance Wood]

Thank you all for the winter hardening advice.

A related question for those of you who allow freezing, what effect do you see on akadama? This is my first year using akadama, and it may break down more quickly with freezing?

I don't know, I have heard that it breaks down under those conditions, but I have never been so unsatisfied with my soil mix to shell out the expense, associated with the stuff, to try it.

 

[JudyB]

James, I have had trees that came to me in akadama, and after 1 or 2 seasons in our freeze thaw cycle, it had broken down into a mucky state, and compromised drainage and health. I repotted asap into different substrate that works for my area.

 

[Vance Wood]

This whole deal about Akadama kind of blows my mind. I know that many who use it swear by it, and others swear at it; but everyone will agree it is more expensive than almost anhything you can use as a soil additive. I think (JMHO) that some people believe because it's imported from Japan it has to be good.

 

[davetree]

Depends on what kind of akadama you have. Some is harder and won't break down as easily. I use the harder stuff and have no problems. By the time anything in my soil breaks down it is time to repot anyway.

 

[crust]

I also think you need to expose your trees to more cold. Like were I live, North Central MN, Sioux falls SD can be a wicked place--especially as far as crazy swinging temps and tough springs. Exposing them to 20 degree weather is a good rule and I believe help lock into solid dormancy. My best scenario is to have leaf drop on everything---larch needles, leaves etc. all come off and a are cleaned off if they don't drop, but then I don't have many non-natives.
Of your species list I personally would not worry about the elms. I have found that they are very adaptable, sleep well and handle low temps well. Tridents, on the other hand, have always resented my MN winters. I would put them away earlier. My trees will remain on the benches until leaf drop which will probably be Halloween. Then they are off to their "cold house", a highly insulated but unheated, solely dedicated building, for a winter of temps hovering from 15-30F. You may have better luck in the spring restraining them if you cover your tunnel with Aluminet shade cloth.