After watching Ryan’s recent video on doing major structural cuts on a Japanese maple im planning on doing the same in few days. My JM is approx 10 yrs old acquired from Ed Clark. It needs major structural work. Luckily im not in an area that gets bad freezes. (I’m in central California)Usually it gets just below freezing here but not much more. Now i know normally in my area my JM don’t need cold protection, but considering major structural work should it be protected in a green house or mulching over? Please help, thank you.
If you have the capacity to protect it after structural work, why not do it this season? Any post leaf pruning will reduce some of the winter hardiness capacity…how much…nobody could really say so I wouldn’t roll the dice
I do have the ability with a greenhouse. Ive also heard not to protect it in my area. Thank you.
“not protecting a Japanese maple” is too broad of statement to have any utility. At best it’s context dependent… but why not protect it? If thie statement is root d from the fear is not letting it go into full dormancy and eventually dying from carbohydrate depletion and the alternative is "to not protect it. At best, that’s partially true but the timeline for a JM is multiple years of reoccurring non winter dormancy.
Typically yes it’s best to let any tree handle what ever winter hardening temperatures as possible but it will depend on the strength of the tree.
I would aim to keep it above 28°F but below 40° F under a shade cloth for the winter if I did structural work in that fall.
After structural work I would probably keep it in the greenhouse at 32 - 40F (0 - 4.4C). I keep all but my seedlings under those conditions, however, I have lost seedlings at temperatures below 10F (-12C).
Thank you for the information. Regarding seedlings they can take colder the 32*? I have 2 month old Japanese black pine seedlings outside and was worried about them getting too cold so ive kept them in greenhouse at night and brought out during day in sun. Can they stay out? Its getting down to about 30* f here.
Hagadorn lists the root zone kill temperature for A. palmatum as 15F (-9C) and the top kill as -20F (-29C). Seedlings and most of the cultivars are more prone to cold damage. I think your seedlings will be fine down to 28-30F, particularly if there is something between then and the night sky. Radiant cooling to the night sky at 3K (-270C, -454F) can result significant cooling below the air temperature. On the other hand, placing thing in good contact with the ground can result in warmer than the air temperature. Under the bench, on the ground is a good choice and tossing a sheet over the bench to the ground will provide even more protection on the colder (low 20s F, particularly if it warms during the day) and avoid the bonsai shuffle.