Question of lighting based on temp.

Neild

I have read about all of the overwintering threads and have not seen this question answered. Most people it seems either winter conifers outside with mulch & windbreak or in a cold frame with some filtered light.

If I overwinter my evergreens (boxwood, chameacyparis, black pine, mugo, juniper) in an unheated garage with no windows, zone 5, Indianapolis area, does it seem logical or even directionally correct to turn on a flourescent full spectrum grow light when temps hit 40 degrees or above? This my 1st winter with bonsai trees.

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midwestbonsai

Good question.
All I know is that once a tree goes into dormancy it does not need light.
But I do not know if they suddenly break dormancy because of temps, I think it has to do more with the length of the light/darkness.
Hope this helps.
-Paul

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soonami

I think that with evergreens, they do need a certain amount of light and scheduled amounts light would not be a bad idea. As I understand, lower levels of light is what pushes a tree into dormancy but temperature is the biggest factor in bring a tree back into active growth.

Neild

I have read that it is primarily tempreture, but light plays a role also. To provide enough light to break dormancy I would imagine I would have to provide a more significant level of light than this 1 flourescent grow light can provide in a life time. Does anyone have any thoughts as to what tempreture to use as an indicator to turn the light on?

bwaynef

I'd assert that all of those varieties are tolerant of the cold, and that putting them outside won't hurt them. Thats not really an answer to your question, so what would it hurt to put light on the trees? If they DO in fact need light during dormancy then they have it, otherwise it won't hurt them.

(Notice I'm staying away from whether they need light or not.)

WF

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rockm

Trees with no leaves do not need light. They are incapable of using it since their photoreceptors (leaves) are gone.

Since conifers (and broadleafed evergreens like boxwood) are evergreen and are capable of photosynthesizing year round, they will probably do better outdoors in the light than inside in the dark. They can take some low light conditions, but why push it?

You also assume that dormant trees will become active again just because the temperature reaches above 40. That's not really true. The length of dormancy is determined genetically. Each species has its own unique "chilling" requirements" that is must fulfill before beginning active growth again. This varies greatly, but in general, it's not a short amount of time. This prevents too early bud break in trees in the wild when a warm spell hits at the beginning of January. Trees are dependent on soil warmth as a signal to begin growing again once the chilling requirements are fulfilled, though. It takes some time, however, for the soil under mulch to warm up.

dtree

The weather can be pretty harsh here in Minnesota and I winter all my trees in an unheated garage. Evergreens go under a north-facing window for indirect light. I have not had good luck with several different methods of wintering trees outdoors here including mulching, digging a big pit and mulching, and wintering near the side of the house and mulching. I always would lose a few trees, including pines and juniper, when wintering outside. Inside, no losses and evergreens seem fine and healthy. Am I slowly weakening them by using this method ? If there is a better method for zone 4, can you help me ? Thanks.

dtree

The weather can be pretty harsh here in Minnesota and I winter all my trees in an unheated garage. Temp. is 25 -35 degrees. Evergreens go under a north-facing window for indirect light. I have not had good luck with several different methods of wintering trees outdoors here including mulching, digging a big pit and mulching, and wintering near the side of the house and mulching. I always would lose a few trees, including pines and juniper, when wintering outside. There seems to be a lot of extreme freeze/thaw stuff going on here in the local climate. Could that be the reason ? Inside, no losses and evergreens seem fine and healthy for 5 years now. Am I slowly weakening them by using this method ? If there is a better method for zone 4, can you help me ? Thanks.
dtree