It's really not a matter of leaves hardening off - more a matter of leaves having time to turn the corner from being an energy sink (net user of energy) to a net producer of energy. When a plant loses its leaves in late summer, it is particularly taxing to the plant. In plants, energy must come out before it can go back in. Your tree will have used substantial reserves (likely nearly all) to produce the new flush of foliage, leaving it very low on reserves at a time when energy reserves are normally peak. Leaves on deciduous trees are net users of energy until they are about 75% mature. At that time, they begin to "pay back" what they borrowed from the tree's reserves. What happens next spring will depend on how much energy the plant is able to store before upcoming leaf abscission. I would not prune anything or disturb roots this fall and would not consider a spring repot. If the plant happens to be root-bound now, pot up in spring instead of repotting. More than cambial tissues, the roots hold stored energy and your tree will need all it can possibly get to keep its systems orderly over winter & put on a new flush in spring.

Al

I suppose protecting the tree from the first several frosts and allowing it to gain a little strength before entering its winter dormancy might help a bit. Tridents are very strong trees and can be defoliated multiple times during a growing season if properly maintained. Good luck,

Dave

I agree that Acer b. is very vigorous by nature, but even the most vigorous of trees can easily be killed by late season defoliation. It is well known that deciduous material is usually at its weakest after the spring growth push. Reason: Woody plants typically use up nearly all their stored energy to put on a flush of leaves. Normally, a tree is at its peak in stored energy in autumn, when leaves fall. It uses some energy in the dormant and post dormant period before buds move in spring, to keep its systems orderly. Building leaves is extremely taxing, as you can see by the observation the tree goes from near maximum stored energy before leaves form to nearly no energy after.

If the leaves have not grown to maturity, they will be using all (or nearly all) the photosynthate they produce & storing none (or nearly none). In my view, this is a serious compromising of the trees survival ability.

So, I suppose my point is that even a properly maintained tree that might have the genetic vigor to allow repeated defoliations in a single growing cycle should not be defoliated late in the summer. Even though John's predicament was unintentional, the effect is the same as if he had mechanically defoliated the tree, or worse, depending on what the cause of defoliation was to begin with.

Leaf abscission is largely a function of decreasing photo-period. The flow of auxin across the abscission layer slows as light intensity & day length both diminish. This causes a corky layer to form at the base of leaf petioles. Water, nutrient, and metabolite flow to & from leaves stops. It's possible, even probable that moving the plant indoors to protect from chill (I noted that you said frosts, so this isn't a contradiction of your statement. I agree that frost protection is a good thing for this tree) could hasten leaf loss due to the reduction in light available.

Al

Al, I agree with everything you said. Still, I think John was interested in more then just info on plant physiology and prognosis for his tree. As you mentioned, he can't change the fact that his tree is pushing new leaves in October. So...protecting the tree from killing frosts and allowing it to gain any strength at all in the best lighting available (The bonsai 2-step), and then letting it enter dormancy later in the year may be more helpful then just leaving the plant as is. His options are limited, so we give him the best one.

Dave

ps. I was a botany major a long time ago...nice review of leaf abscission. I hadn't read or heard the description of this process in 18 or 19 years, but your tutorial sure brought back memories. Luckily, no exam this week!

How much of a dormancy and at what temp range (for dormancy) does the Trident Maple require? We have very mild winters here in zone 8. I am concerned about it budding too early after leaf drop (new maple owner) and what the cons are concerning defoiliation next summer etc. Thanks

SA