I am glad you found the information beneficial and helpful. I will continue to provide information as my ability allows. A few more things to consider about pruning Japanese maples. -Keep your pruners clean, sharp, and sanitary. As a side note: My favorite pruners are Okatsune 103 or 104 8.25-inch Bypass Pruners. The Okatsune are extremely sharp and stay that way because they use the same high quality Japanese steel and the heat treating processes that is used in making samurai swords. They cut great and have a great feel and balance too. -Get a pair of needle nose pruners for pruning back delicate new growth. I like Okatsune Professional Snips, No.207 or Okatsune Bonsai Scissors, No.206 for a longer reach. Why not just use regular bypass pruners for tender new growth? I find bypass pruners can destroy the vascular system of new growth as it tends to compress while cutting this tender growth. Just ask anyone who has successfully rooted cuttings on a consistent basis. They may use bypass pruners to collect their material, but great care is used not to damage the vascular system when cuting and preparing the cuttings for rooting. Most who understand use a razor blade held at an angle and roll the twig to slowly and evenly cut into the twig. To use the razor blade and pushing straight thru the soft tissue would crush and destroy the vascular system much like a bypass pruner, resulting in a failure and no roots. What does this have to do with pruning? If you crush the stem while cutting tender new growth, then you increase the risk of disease and tip failure (or branch failure) back to the main branch. A pruning scissor will get into hard to reach areas, cut cleaner, and cause less damage when cuting tender new growth, whereas bypass prunerso are meant for older hardened branches. When using a bypass pruners make sure the blade is on the inside of the cut. The metal guide should only contact the part being removed. The blade should be the only thing that touches the remaining part of the tree. Why pay attention to this detail? The metal guide crushes, pulls, and damages the bark or branch collar. The cut then takes much longer to heal. When the guide damages the part being removed, it's no problem, and the blade makes a clean cut on the remaining tissue allowing it to heal faster, thus reducing moisture loss and the risk for infection. It's all about using the right tools and the right techniques. -I use 92% alcohol to clean and sanitize. I choose to skip the bleach as it ruins the finish and dulls the blade. -Sanitize between cuts on known sick trees to limit the risk of spreading the outbreak to other areas of the tree. Otherwise sanitize before moving on to a new tree to prevent the spread of disease. As for the regretted decision to prune in winter, my advice is to not wory. Really it comes down to risk management. We need to consider if our decisions are helping or hurting our trees and learning why. By pruning in Winter we need to consider the risks. One risk is of bacterial outbreaks. Japanese maples are one of many woody ornamental that are highly susceptible to Pseudomonas. The cold dry air dried out the cambium layer, slowing healing, and carries a higher risk of damaging the branch collar which opens the tree up to wood rot fungi. Sounds bad but keep reading... Now some things work in your favor when we consider that your tree is Acer shirasawanum which tends to be more cold hardy. They tend to heal quicker and their bark is thicker and stands up to moisture loss better than palmatum. They also tend to be less susceptible to bacterial outbreaks. Although I would not promote pruning them in winter, the good news is that you have factors that lower the risk of having a problem when we take all things into consideration.
Thought I would do an update, almost ten months after this fascinating and informative thread was started. After a rocky start in the spring, when hungry winter moth larva threatened to defoliate this tree (but I managed to keep on top of them and removed hundreds - ewww!), this Acer Shirasawanum managed to put on some really great growth. Here is a close up of the area I cut off without leaving a stub to dry out. Fortunately it seems to have been okay. I need to rub off the sprouts that are near the pruning cut. Here's another view I will take out these little leaves and the in-growing tiny branch now to make sure there isn't a giant wound that disfigures the bark. You can see the rotted stub above the junction point with all the little sprouts wanting to grow. It's definitely deadwood but I am afraid to cut into it since it goes almost to the join and close to when the new branch growing at 11:45 is. I'm afraid if I cut away the bad wood it might damage the young branch. Thoughts? Hope you all enjoy the fall colo(u)r display which is around the corner! Cheers.
