I have spoken many times about how pruning Japanese maples over Winter is a bad idea despite many books encouraging such activity. I have found they heal or form wound wood faster when pruned in May. Below is a study finding Japanese maples do not heal from winter damage. When cuts are made when temperature is at 15C or 59F trees start to heal within a three week period. This information in combination of high risk of bacterial disease in late Winter thru early Spring (Feb-mid April in my area) should be evidence to restrict Winter pruning of live wood in Japanese maples. "During winter dormancy, temperate trees are capable of only a restricted response to wounding. In an experiment, we investigated the effect of wounding on Acer palmatum trees during winter-bud dormancy and found that in the cold (4 °C) temperature treatment, wound reactions were virtually absent. In the warm (15 °C) treatment, however, trees reacted actively to wounding within a three-week period by e.g. forming callus and local wound xylem. We conclude that temperature is an important factor in wound reactions during winter dormancy and may even induce the formation of callus and wound xylem within a three-week period." Why don't Japanese maples heal during cold dormant periods, it's though cold temperatures inhibit biological wound signals that triggers important hormones: "This suggests that in our experiment the local formation of wound xylem in A. palmatum was triggered by a wound signal that is active only at a higher temperature. The wound signal might comprise hormones such as jasmonates and ethylene, which are important in wound closure" Pruning during the dormant season increases the risk of bacterial diseases because the trees ability to compartmentalize and stop the spread of infection is inhibited by cold temperatures. The risk is highest in areas of cold and wet climates in Spring before the tree breaks dormancy. This may explain why in these areas Japanese maples are prone to black tips after Winter pruning. When I stopped Winter pruning I no longer get black tips in Coral bark maples and other prone cultivars. "compartmentalization by inhibitory compounds is a temperature-dependent physiological process similar to the formation of ligno-suberized layers, callus and wound xylem, which are all delayed at low temperatures during winter dormancy. Given that compartmentalization of tree wounds restricts moisture loss and damage from pathogens (Shigo 1984; Mireku and Wilkes 1989; Pearce 1996; Fink 1999), it thus seems likely that trees in areas with mild winters might cope better with the effects of wounding than trees in areas with cold winters." Early wound reactions of Japanese maple during winter dormancy: the effect of two contrasting temperature regimes - PubAg Full text: Early wound reactions of Japanese maple during winter dormancy: the effect of two contrasting temperature regimes Reconsider Fall pruning as it can be too cold to heal in some climates: "In a garden experiment, Copini et al. (2014) found that A. palmatum trees that had been wounded in October when most leaves had abscised had formed no local wound xylem or callus 14 or 28 days later: in the 14-day period the average temperature was 7.3 °C (±2.7) and in the 28-day period it was 8.2 °C (±3.3)."
Hi JT1, Very interested in your posting, we have always pruned in Autumn after last leaves have dropped. This is due to nearly all books saying to avoid pruning in Spring due to rising sap. Have you had any problems with your maples with your method? We are about to move our whole collection (150 maples) in the Autumn and was going to prune then for house move, would you suggest leaving it to the Spring? Thanks for a really good post.
The sap starts to flow usually in late January to early February, but it's weather dependent. Once the trees leaf out and put on their Spring push of growth you don't need to worry about the sap bleeding from pruning cuts. Pruning too early in Spring (after the flow of sap but still dormant) before the tree breaks dormancy carries the risk of bacterial infection. In my area the risk is highest for disease from February thru mid April when the ground is still very saturated from the Winter thaw. We remove grey dead twigs over Winter but we do not make the cut into live tissue. We cut the dead grey twigs back to live bark but do not cut the live bark, the pruning cut is made into grey dead tissue flush. If you are moving then I would go forward with your plans. It's better to prune and prevent accidentally breaking branches during the move. Since you have done Fall pruning in the past with no problems you shouldn't worry. Areas with a milder Fall may have adequate time for the tree to start the healing process and compartmentalize the wound from freeze damage and disease. Our area is very unpredictable as we can have snow for Halloween and prolonged periods below freezing in November. I am in a high risk area where your area carries less risk. The following season you may consider Spring pruning during the growing season, you may find the wounds heal quickly and your trees may be healthier as a result with less Winter damage.
Hi JT1, many thanks for the great info, our Autumns are very mild indeed, so we will continue this season with pruning in October. It will be quite a hard prune this time to enable wrapping of branches to move safely. In 2020 we will try your method as it's always interesting to look at different ways to care for maples. My wife and I have been growing maples for 40+ years (hence the quantity), but one never stops learning. Thanks again.
I agree, we are always learning too. I find our trees are great teachers when we devote our time but most importantly pay attention to what they are trying to tell us. Then the internet opens up a world of research / experience that I never would have access to otherwise. The effort we put into our collection repays us ten fold in ways I never thought possible. They would definitely be coming with us in a move to a new home. It's great to hear both you and your wife grow maples! Both my wife and I enjoy, but we are only about half the number and time growing. We always talk about what we might do if we ever move. Good luck on your move! I assume it's both nervousness and excitement. Nervous about moving all the trees and getting them to their new home, but at the same time exciting to get a new place to do things right. It's like starting over with having everything figured out. This should take things to the next level having experience as a solid foundation in finding the best spot for each tree / cultivar. Please keep us posted, take some pictures. I'm sure many people can benefit from the experience gained in moving such a large collection. Thanks for sharing and your feedback on the study.
Hi, JT1, I just bought my first Japanese maple (Acer palmatum Osakazuky), and I'm planning to keep it potted on my terrace (I don't have garden). It's still a very young tree, but it already has one really long, quite thick, side branch (or maybe main branch?). I was actually thinking about cutting it a little bit, but after reading for hours I still don't know if it's smart thing to do (just for prettier looks and future shape of the tree). Also, it's springtime, but still chilly at night. Should I wait a little bit before pruning? Thank you in advance for your advice!
It’s tricky to tell from the photos but the longer branch appears to be grafted on the green root stock, and so you would expect that branch to be your named cultivar..the other branch looks like it’s growing from below the main graft..this could be the rootstock cultivar growing out..or it could be the grafter has attached two grafts on the single roof stock.. do the leaves look identical on both branches or are they different? They appear the same..which indicates two grafts maybe..if they are the same I’d let them grow out maybe put a bamboo cane to hold it a little more upright..you could end up with a very nice shaped tree
Dicky5ash - this was also my dilemma - which one is grafted? Leaves are very similar, but I'm not sure they are identical (that's why I need experienced eye). Lower branch leaves are nicer, but maybe they were just less exposed to wind than other ones? So, you don't think I should cut it short? Do you think it would be damaged? I was hoping to achieve little tree or bush-like composition, especially since it can be windy out on the terrace (and shorter tree would be more protected). Here are some daylight photos, maybe they'll be better. Hopefully I'm not spammimg! Thank you for your opinion
Hi Aleksandra, I agree with dicky5ash, the only thing I would add is to not do any pruning now when the sap is rising. Also the tree is under a certain amount of stress already from moving its location, you don't want to add to that stress. I would leave it alone until July and then consider shaping, although it could be a very interesting shape as it is and look great for years to come on your balcony. Hope that's a little bit of help.
Ever since i started with maples over twenty years ago now, the only thing i do every year with out fail is lift and root prune all my ground maples which are to be containerised or moved for the following year, and of course all major limb/branch pruning is also done in the winter months as well. Could post literally dozens and dozens of pictures of all the work i have done over the years with no adverse effects on the trees what so ever !! Have never worked on anything during the spring time and never will (the sap is rising) why are you wanting to start cutting things back?? Now i now their are numerous people out there who will totally disagree with what i do , that's ok with me but i know my trees but more importantly i know the weather conditions in the UK and over a period of many years there is definitely a marked warming every year during the winter time which helps greatly with the work required during the dormant season, now if i lived in an area which suffered brutally cold winters then of course it would be a different scenario/regime to follow, but at the end of the day i have personally found a period of time during the year where i prefer to do all my maintenance work and this works for me (and my trees) and that's all i can say ??
What causes die back? I'm trying to get my bloodgood to grow large as it can get, but it seems to be self pruning. It looks good until the end of winter, that's when I noticed the tips of a few wood dying back. Around 4-8" of die back. So I prune them. I think I put some fertilizer at the same time. Maybe that caused it.
Everyone gets a bit of die back here and there, not a lot, the odd unexpected branch or several shoots that didn’t make it through the winter..it’s just nature..however the 4-8” should be an exception and not be across all branches..that would indicate an underlying problem..
@ROEBUK, what do you mean by "the sap is rising"? In addition to maples in my landscape, I grow maples as bonsai. I routinely do root work in the course of repotting in spring, before leaves are emerging. Does "leaves emerging" = "sap rising"?
