Cold soil inhibit breaking dormancy in spring?

Discussion in 'Maples' started by Arktrees, Feb 19, 2012.

  1. Arktrees

    Arktrees Member

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    Hello all,
    I have a question that I hope someone can help me answer. Basically, if a Japanese Maple is planted in a spot where it's root zone will be shaded in the winter, therefore the soil will have less chance to warm on a daily basis, will this result in a slower start in spring?

    I live in a river valley of Northwest Arkansas, with hills surrounding. This results in a micro-climate that is typically colder on the "cold" nights than the surrounding area. As such we get last hard freezes that can do allot of damage. The effect is severe enough as to deter us from planting most Japanese Maples. I have taken to acquiring small specimens and keeping them in containers for 1+ years to determine when they will leaf out locally. One of these I currently have is a Bihou, and would really love to be able to plant out. We have a location in mind that has a privacy fence that blocks the winter sun from reaching the ground, creating a area of relatively cold soil temps in winter. So that begs the question, will this cold soil slow the break of dormancy in the spring? I have looked online for hints of the effect of soil temps on dormancy, but didn't come up with much. So I though it possible that someone on here might have a comparison where an individual JM was planted in a sunnier spot, compared to individual of the same cultivar planted in a much shadier local close by.

    Any insight any of you could give me would be most appreciated. Thank you for your time.

    Arktrees
     
  2. Gomero

    Gomero Well-Known Member Maple Society 10 Years

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    Hi Arktrees,

    Did you read the thread http://www.botanicalgarden.ubc.ca/forums/showthread.php?t=71965&page=2 where the effect of soil temperature on root growth was discussed.

    My understanding (I am not a botanist) is that the main triggers for breaking dormancy are air temperature and day-length. The relative importance of one another, and the actual values needed, are species dependent. I believe that when a tree breaks dormancy, it uses the reserves existing in the branches, trunk and roots, made before going dormant; it does not depend on root activity for early supplies. Anyway, according to the article I quoted in the thread above, as long as the root-zone temp > 6-7°C, then roots are ready to start growing again.

    Gomero
     
  3. JT1

    JT1 Contributor

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    I think we may be talking about two different things. The roots usually don't go into a true dormant state. The roots may temporarily stop growing when the soil temperature drops below a certain level. But what's interesting is how when only a portion of the soil is warmed, only the roots in the warmed area will grow while the roots in the other (cold) areas do not (all on the same plant).

    When a tree is in the final stage of dormancy (post-dormancy) the bud is capable of growing but it's suppressed by the low soil temperature. (Day length plays a role too, but I feel temperature is the driving force in my area. Moisture can play a role also, as water stress will deepen dormancy. The variety plays a role as some break dormancy later than others)

    When the soil warms, growth promoters such as cytokinins and gibberellin build up and signal the buds to resume growth. It's a cumulative effect of time spent at the warm temperature, that's why a warm stretch in late winter does not cause the buds to break. It's my understanding that the accumulation can be anywhere between 500 and 2000 hours of soil temps above freezing.

    So I think your proposal has some merit, but to what degree. It’s my opinion that it may help the tree get a slower start to spring to a certain degree. But it may not be slow enough to eliminate the problem you’re faced with being in an area where you are the last to experience frost or hard freeze.
     
  4. Arktrees

    Arktrees Member

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    Thank you Gomero, I had not read that thread, but will do so. I appreciate that day length, temperature, etc are very important in breaking dormancy. We have allot of plants doing so now 4-6 weeks earlier than last year.

    JT1, thank you for your input. I had considered that any possible effect might be reduced as the tree got larger, but I also believe it would be most sensitive while smaller. I do not expect any effect to be overwhelming by any means. After all the difference in temperature is not likely to be large, a few degrees at most. However it if it were enough to buy 7-14 days, with a cultivar that is 7-14 days later, then it may be enough. I am typically 3-7 degrees colder than surrounding areas. It just seemed logical that there would be some amount of inhibition, as roots being in cold soil would seem likely to be less able to support top growth. Therefore it would seem beneficial to plant survival for there to be some effect.

    I currently have the tree in a fabric root pruning pot. I may plant pot and all (this is common) now, and see when the tree leafs out, though I would have preferred thinking of this last fall, so that it would have been in this environment the entire winter.

    Thanks again for you time,

    Arktrees
     

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