I recently acquired a collection of trees that the owner was unable to maintain. The worst suffering had not been repotted for some time, to the extent that the drainage holes are occupied with roots almost as thick as the hole itself, and drainage is non-existent. In the canopy, branches have been lost and growth has been extremely limited for at least one year. The trees were inadequately watered and though I can’t be sure, I’d say haven’t been fertilised for a long time.
Common advice is to slip pot into a larger container without doing any root pruning. But I’ve been bitten by that in the past with conifers.
Does there come a point where a tree is so badly in need of repotting that it is too weak to be repotted?
Should one perform a very conservative repot - simply aim to free up the drainage holes and remove any dead matted roots from the bottom, so that water/oxygen can drain/enter the system (respectively)?
Should one avoid repotting completely for a season and instead use the various techniques for improving percolation and water removal in the hope the trees can regain enough strength to survive a repot?
The species I’m concerned about are western hemlock and japanese larch. Broadleaf species that were in the collection I am more confident to handle.
I took over a few trees from the daughter of the artist that owned the trees and sadly passed away. I had to wait until the upcoming spring to think of repotting anything. I was only able to repot one of them. The others were too weak, so I left them alone for a year. This year the rest will be repotted as they’ve responded well to the year of care.
If the percolation is that bad it may be worth doing the repot this spring. Better yet, pull them out of the pots, do some root work, and then put them into development boxes to allow them to regain strength.
If you feel like they’re just too weak you can use duct tape to build a wall around the rim of the container to allow the water to pool and eventually seep into the pot.
I, too, am not a fan of slip potting. The water ends up just flowing around the root ball instead of watering the tree.
You should be able to do a fairly conservative repot of the Japanese Larch (Larix kaempferi) as the buds just start to swell (if you can see more than just a bit of green at the bud tip it is getting late - proper time to too late is often a few days). I would remove the obviously dead/totally matted roots, loosen the rest of the rootball a bit, and pot into a similar or slightly larger pot depending upon how much you take off. I think you will find they do fine this coming year and explode the following year to set up for a full repot in 2023.
No advice on the western hemlock (Tsuga heterophylla) since i have managed to kill the ones I had.
With the western hemlock remove it from its pot. Assess the damage (if any) and remove any dead roots, tease out the roots around the edge and loosen some from the bottom. Then repot into a slightly larger pot. Allow it to regrow freely for the next 12 - 24 months then you can treat as normal.
I agree with Marty, the time for repotting larch is critical. Just as green is peeping through the bud is the correct time. There is an idea you should do it before this but (and I have experimented with this) if you do it too early the tree will be very slow to recover and growth will be weak for the whole year. In the UK this time can be anytime from the start of February.
Michael Hagedorn in “Bonsai Heresy” recommends saving distressed trees by putting into pumice in a box or anderson flat. I have done this to both a Ponderosa pine that was very much too wet, and a Douglas fir that had few roots. The pine is getting healthy and growing well, The Douglas fir died. So my personal experience is mixed. I believe that a tree must be vigorous and healthy before considering a repot or transplant. I have an ICU where very stressed plants are treated, and a recovery area where plants are allowed to grow freely to regain strength. My ongoing goal is to avoid bad practices and reduce the number of stressed and damaged trees! I am grateful to this forum teaching me what has worked well for others.
But be very careful to not disturb the roots any more than necessary. I try to remove blackened dead roots and keep the very fine roots encased in good soil.
Just getting the trees out of their pots will cause some roots to need pruning as a result of using the Kama - which will be absolutely necessary.
It’s a choice between moving them into wooden box and pumice with as little root disturbance as possible, or, build a wall to aid percolation and tilt the pot to help water out of the pot, and hope I can improve water/o2 balance.
I’ll tentatively investigate the soil to see if the akadama is completely broken down (I’m almost certain it is) and make a choice from there.
Any other pointers between now and spring welcomed!
You could, if you have spare pots simply place the existing pots into large ones and let the roots grow through the drainage holes which will invigorate them, You could even place the pot in a position on the ground to allow roots to grow down into the ground. You still retain the close roots to the trunk and the tree will return to health. Water and feed the pot not the ground. This is virtually guaranteed to rejuvenate your trees without disturbing them and repotting in twelve months will be a breeze.
I believe that a tree must be vigorous and healthy before considering a repot or transplant. I have an ICU where very stressed plants are treated, and a recovery area where plants are allowed to grow freely to regain strength. My ongoing goal is to avoid bad practices and reduce the number of stressed and damaged trees! I am grateful to this forum teaching me what has worked well for others.