The "brand-new potting mix" is gritty mix.

Neither approach will help it tolerate repotting better. In fact, the information provided to cut it back by 1/2 to 2/3's is erroneous. While canopy pruning to reduce transplant shock has been a recommended treatment in the past, it has been proven scientifically to be a detriment to successful re-establishment and is no longer advised.

The foliage canopy of any plant, and most especially evergreens, is an energy producing factory and the plant needs every bit of this 'factory' in place to recharge and power the root system. And a healthy and active root system is what is going to see the plant through any repotting or transplant shock.

You can get away with some canopy removal in fully deciduous plant material while these plants are fully dormant - no photosynthesis is going on at that time - but I would avoid any trimming, shearing or branch removal on anything evergreen. If the plant is unwieldy and difficult to handle as-is, you can wrap or otherwise carefully gather the branches together to repot but don't cut them off.

Hi gardengirl48,

About a month ago, I posted questions about the method, timing and preventing "repot shock" when planting Eugenia Myrtifolia (brush cherry) in "gritty mix".

On September 22nd, Al Tapla responded by saying "If you had removed about 2/3 - 3/4 of the canopy at repot time, it's very likely the plant would have recovered instead of collapsing".

Far be it from me to question any of Al's recommendations - he is my
container gardening guru as well and I have known him for years - but
this is a pretty widely accepted horticultural concept with dealing with
any plants growing or to be planted or transplanted in the ground. For the life of me,
I can't think why it would be any different when dealing with a
container planting. Unless you dug this plant from the ground to put in a
container and subsequently damaged or severely truncated the root system. THEN, cutting back might make sense. Otherwise, it is the foliage that fuels root development, not the other way around, and removal of a significant portion of the foliage will only delay root development and re-establishment.

Just to clear things up. I fully agree that plants going into the landscape need the foliage to make the food that allows the plant to increase root mass. It makes perfect sense as a general rule/practice. It SEEMS like it should make sense for containerized plants as well, but in reality, you always have to be able to make a judgment call.

I think the easiest way to provide some perspective is to call to attention the fact that trees are genetically programmed to keep a rough balance in the root:shoot ratio. Root growth always precedes shoot growth. If you defoliate a tree, a lot of roots die. If you root prune under certain circumstances, the canopy dies back to whatever volume of branches and leaves the root system can support. So nature already does this balancing automatically.

I've lifted from the landscape or collected from the wild a fair number of established deciduous trees while in summer leaf as potential bonsai. That doesn't mean the root ball I collected was small or they went into a small pot. I'd collect them with the largest root mass I could handle & often built special wooden containers for them to accommodate the root mass. Until I started significantly reducing these tree's canopies, they almost all collapsed. This occurred even if I put the tree in shade out of wind, so we can be sure it would be harder on the tree if it was lifted and was going to go immediately back in the landscape in a full sun position. So we have to allow some wiggle room in what everyone wants to see as clad in stone.

Bonsai practitioners do a LOT of collecting from the wild, and from landscapes, so there is a LOT of info out there about collecting. Basically, it says if you're going to be reducing the roots significantly while trees are in active growth, you'll want to reduce the canopy for 2 reasons. The first is to prevent total collapse of the organism. The second is less serious, but it also prevents the tree from indiscriminately shedding branches that might be important to the composition.

In trees that have been repotted already (say 2 years previous) it's usually not necessary to reduce the canopy in a regular root pruning session, but if you're maybe moving a tree from a large training pot into a bonsai pot and have to remove a very large fraction of the roots, reducing the canopy might be necessary to prevent either of the two things I mentioned from occurring.

You'll note I mentioned 'collecting' above, but there's not much difference between collecting and repotting, if during the repot you're removing half or more of the root volume. Repotting dormant temperate trees gives you a little bit of a break when you remove a notable volume of roots w/o reducing the top mass because the tree only brings back on line the number buds the existing root mass can supply water to. As the root mass increases in volume and ability, more and more buds will be activated. Very often though, a fair number of the most distal buds die, which is the tree acting to balance roots with shoots.

Your tree (ok shrub - everything's a tree to me) would prefer to be repotted around the vernal equinox where you live. Repotting it now will probably be ok if you can keep it outdoors. It back-buds like crazzy, so there is little reason not to cut the top back hard if its healthy. If it's not, make it healthy & repot then. The tree doesn't care if you shear or prune, but you will in subsequent pruning sessions because shearing will provide you with a nice knot of up to a dozen branches all coming from from one spot. If you reduce by pruning, you can go through the tree and remove all the trifurcations, which is it's natural growth habit. Then you can cut the remaining long branches back to smaller branches, or just to a leaf or bud that's erupting on a bare branch. It's a pretty forgiving plant - especially where you live. I have one I've been tending for 5-7 years that was about ready to go into a pot, but either a deer or squirrel ate the top right off of it - chewed through the trunk at a point where it was thicker than my thumb and either ate it or carried it away. ;-(

Al

My Eugenia Myrtifolia brush cherry is about 2-feet tall growing in a 2-gallon plastic container bought from a nursery.

I intend to wash all of the original potting mix from the shrub's roots before re-potting the shrub in gritty mix (to eliminate the PWT resulting from different compositions of growing media).

Since I don't intend to reduce the volume of the roots, should I reduce the canopy? If "Yes", how much of the canopy should I remove?

I would reduce it. I regularly reduce the canopy of tropicals significantly at repot time, mostly to prevent the tree from shedding the branches I've already painstakingly developed and consider vital to the composition. Even though you're not going to reduce the root mass, you ARE going to put a lot of stress on the root system, so I'd reduce the canopy by 1/4-1/3 by eliminating trifurcations; this achieved by cutting the lower order branch back to a pair of higher order branches. Branches attached to the trunk are first order branches. Branches attached to first order branches are second order branches, and so on. If you have a branch that trifurcates, the center of the trifurcation is 1 order lower than the 2 flanking branches.

My trees are always healthy or they don't get worked on. Almost all healthy trees other than conifers have enough energy reserves to push a new flush of growth, even if completely defoliated. After you've gained some additional repotting experience, you'll begin to develop a sense of what needs to be done in certain sets of circumstances to ensure the plant doesn't just collapse. If a tree is healthy, I find it's often much better to reduce the canopy well beyond the point that ensures the plant won't collapse and wait the weeks for the plant to catch up than it is to risk being just a wee bit short of that 'total collapse is ensured point' and end up with something to be added to the compost pile. We don't want to unnecessarily go too far when we reduce the canopy, but until you develop a feel for what 'too far' might be, better safe than sorry is probably the operational tack best taken. IMCO.

Al