Very good information.

Ah, so I guess all maples can tolerate root-pruning. That's good to know.

What other trees have you grown in such a fashion? I am rather curious about all this!

Thanks for the info!

Hello, Al-
thanks for this elaboration. i was looking for info like this, since it also helps with the initial planting of containerized trees, and the type of analysis one should do of a rootball.
I have a few questions: the first concerns the larger roots which you write are practically speaking useless in container culture. In larger container - I have 40 gallon types, with an 80 cm (31 inches) - wouldn't they help steadying the tree against the wind, for instance? I understand you prune mostly underneath the trunk - and hence not upper roots: would these then hold the tree?
I also have two questions not directly related to pruning, but the frequency of repotting: you say slow growing trees can be repotted every 5 years, vigorous ones every 2. You then talk about the different requirements for the media with slow growing trees needing more inorganic matter to help keep the structure. Does this mean you advocate more inorganic matter, and lesser repotting for older trees versus younger (less than 10 years?) trees, or is this strictly an species/cultivar related issue? You do say that older trees tolerate rootpruning less than younger trees - why is that? How about specifically maples in this respect?
Finally, if it's not too much to ask in one posting, and keeping in mind this has to do with pruning: you underline the need for the fine roots for water and air purposes, and suggest with rootpruning the right type of soil. What about nutrients besides water: if the media drains too well, does this not deplede the soil too quickly of nutrients?
Thanks again. I realize not all my questions pertain to rootpruning.

Rad - The list of genera is long & I treat almost everything except conifers this way (some pines, junipers, etc., don't tolerate being bare-rooted as well as deciduous & tropical trees with leaves). After the initial pruning, my root-balls are a mass of roots all thinner than cooked spaghetti. When I'm done pruning, most root-balls end up being disc-shaped and about 2-3 inches thick (deep). I grow Malus (apple), Ulmus (elm), Betula (birch), Tilia (linden), Pyracantha, Prunus (plum), Morus (Mulberry), Euonymous (burning bush), Fagus (beech), Buxus (boxwood), Berberis (barberry), Carpinus (hornbeam), Salix (willow), and many more. I also treat All the tropicals I grow in similar fashion.

Schusch - The root mass of trees growing in 40 gallon containers are going to be unwieldy & will probably require assistance. When you're finished, the root mass would likely be near 75 cm in diam & 20 - 40 cm thick and offer some stability, but all depends on how much tree is above ground. I mentioned the value of stabilizing trees after pruning roots to hasten re-establishment When you root-prune & remove old soil, you do affect the stability of the tree and it needs to be protected temporarily against toppling from the container.

You ask a good question about the "top" roots. The roots that originate at the basal flare are pretty much the framework of your root system & the buttress of the tree. These roots are always allowed to remain. They may be shortened to reduce the o/a diameter of rootage, and secondary roots growing straight down would be removed from them, but the buttress roots are not removed unless they are encircling, girdling, or abnormal in shape or growth.

Repotting intervals are determined by the volume of roots or the state of the soil. Roots growing out of the drain hole or crawling over the surface of the soil indicate the need to repot at the next opportunity. Decline in vitality and any number of accompanying symptoms resultant of root damage from collapsing soil and impaired root metabolism is the other indication that a repot should be undertaken asap. Air is just as important to roots as water and when roots are starved for air, the entire organism suffers.

For a soil choice, I would encourage you to find a mix that serves you well when an extended interval between repots is expected & stick with it. You cannot go wrong & unless you have hundreds of trees, expense won't be a major issue. For trees that you will repot yearly, you could use a pine bark/peat/perlite mix, heavy on bark & light on peat, with good results, but it is soo much easier to establish a single, good mix that's primarily inorganic & learn its characteristics. If you branch out into other species, you can modify the soil as req'd. E.g. for junipers, I take 2 parts of my std mix and add one part each of Turface & crushed granite. This gives me a soil that is 4 parts inorganic and 1 part pine or fir bark. Some trees are grown in 100% Turface or akadama - that is no organic component.

Old trees (30-40-50+ years) see a decreasing % of dynamic mass as they age, so they are less resilient. In bonsai, we can treat young material almost carelessly if we choose & expect the tree to be vital enough to cope. Older trees are not as vigorous & cannot be treated this way. Observe the growth rate & (reduced) recuperative powers of old trees in nature for confirmation of this. It's not likely you have any old maples. I'm not making fun, but even a 20 year old maple is a rather young tree.

Another good question about the soil. Yes, the soils I advocate have a price in the form of a need for more frequent watering and fertilizing. However, you will have great flexibility in how/what you feed. For trees that I wish to develop quickly, I am able to fertilize weekly or bi-weekly. My normal supplement program is: A) Water the trees well. B) Apply a full strength solution of 20-20-20 or other balanced soluble mix. C) One week later, water well & alternate with a full strength application of 5-1-1 fish emulsion. D) Return to the 20-20-20 at next 1 wk interval. If you have a tree that is the size you want, you would be able to increase the intervals between fertilizer applications to every two weeks & still keep the tree healthy and happy.

When I mix my soils, I add Micromax granular micro-nutrient blend. I buy it in 50 lb bags & it's expensive (about $75), but 50 lbs will last me 10 years. If any of you are interested in obtaining this product in smaller quantities, let me know. I have a friend that has a bonsai business & sells it for $5 for a half pound. You can also use seaweed extract/emulsion as a source of the minors with good results (Earthjuice, too). You do need to give consideration to your plant's need for the minors - nearly all container soils are deficient. Please do not use compost in hopes it will provide the minors.

I think I got all your questions?

Al

Many thanks, Al- this type of crucial info is not that easy to come by - unfortunately nurseries and other commercial outlets often do not provide any but the most basic directions, often imprecise, cautious or wrong, which, I suspect, leads to the eventual death of many plants.
I planted a couple of red maples - Red Sunset and October Glory, to get more of these fine North American trees into the European landscape - and found that many roots had accumulated at the bottom of the container, creating a dense and hard mass. I realize I was still too cautious when trying to disentangle that mass (impossible, as it turned out), when I should have simply cut an inch off the bottom. What different approach, if any, do you take with roots when you initially plant in the ground?

Thanks again for this.

I usually unpot & use a razor nife to cut 4-8 vertical slits in the rootball, depending on the container size. The hole I dig is about twice the diameter of the roots. I plant with the basal flare above surrounding grade & backfill with soil from the hole only & mulch.

Al

Thank you very much for this information - info like this is very difficult to find and many folks will end up planting trees or growing them in ways that will lead to the demise of the tree since they don't know any better.

That's interesting that you grow beech trees - I always thought they were one of the picky ones that didn't like to have their roots disturbed.

One thing about automatically cutting/slicing roots is that tips of intact roots elongate in fall. I try to wash roots and pull them open when I can. Ideally, of course, you wouldn't be planting rootbound stock in the first place. If there is bad deformity hidden inside the rootball (from when the plant was left too long in a liner or other small container, as is so often the case) you won't catch that without barerooting the whole plant, either.