Root Pruning

Joe1980(5)March 25, 2011

Ok, I have a grasp on the root pruning, doing NOT what the books say. Most books I read say to "trim off an inch or so around the outside of the rootball", which I figure are the productive roots. I trim the old roots, that are more or less just anchoring roots. Anywho, I also have read that when you prune roots, you should also prune the top growth as well, at about the same ratio that you prune the roots. Is this true, or can I just root prune, and we're good to go? Thanks.


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I prune both at the same time. I know there are opinions against doing both at the same time, however, I have found it less stressful for the plant to remove some of the green growth.

I think it depends how severe the root pruning. I typically remove a third of the root-ball. On some plants, I will remove more than half. If I don't remove some green growth, the plant sheds the green growth anyway. I prefer to shape my plants my way, rather than have the plant do it.

I never ran into a problem doing it this way. I have seen plants stressed by only removing the roots and not cutting back the green growth.

Another way is to green prune first, do the roots the following year. If I don't have the luxury of waiting a year, I'll do both at the same time.


    Bookmark   March 25, 2011 at 8:33PM
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rhizo_1 (North AL) zone 7

This is a complex issue when it comes to containerized plants. If we were discussing in-ground plantings, I could tell you with great certainty that you should NEVER top prune a plant to compensate for root loss (usually when transplanting).

Think of root pruning as a way to generate lots of NEW roots...just as top pruning will often result in a flush of new growth just behind the cut. Root pruning is one of the most beneficial things you can do for most containerized plants. And not just removing the old roots, either.

The leaves are what is simplistically called the 'food factories' for plants. Leaves are THE source of energy in the form of carbon resources. When they are removed by pruning, a plant will devote its stored energy reserves to growing more leaves. Period. After all, without those factories, the plant can't defend itself against pests and diseases, can't grow new roots, can't mend wounds, etc.

SO, it is inherently a physiological snafu for the plant...its roots have been chopped, but so have the leaves which produce the energy to make new roots. What to do, what to do? Make new leaves is what to do, at the sacrifice of other functions.

There is also a hormonal pathway that is disrupted when we remove the growing tips of plants, disabling the energy systems of storage and growth of the roots.

SO! What we 'think' makes sense about pruning to compensate for root loss actually has a decidedly negative impact on the plants. We didn't always know this, but science has a way of changing all the time, usually because we have better technology to study the hows, whys, whens, and whatchamacallits of plant growth and development.

All that being said, when I had a good sized collection of bonsai, some pretty mature, I took upon the tasks of root and top pruning with determination. At the same time, I mean. I'm sure that I've done it with other containerized plants, too. But it's not something that can be accomplished without stress to the plant, and that's worth considering. It's better to simply root prune and let the top go with as little pruning as possible.

A bit of shaping, as in Jane's example, is not a problem. I'm referring to pruning the top in the same ratio as the roots....not so good.

Make sense? If not, be sure to email me.

    Bookmark   March 26, 2011 at 6:16AM
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tapla (mid-MI z5b-6a)

Hi, Joe. Just so you can get a feel for how familiar I am with root pruning, I'm a long-time bonsai practitioner (20 years plus), and I often am called on to demonstrate root-pruning/repotting techniques for a variety of clubs and organizations. I also have somewhere between 250-300 woody plants in containers that require regular root pruning.

I can tell you that there are some general rules, but those always need to be tempered by type of plant and your assessment of the plant's condition. For example - you might take the roots of a very popular bonsai subject with a very heavy trunk, trident maple, all the way back to 1" root stubs with no problems. Essentially, you can almost take a healthy 4" thick trident and reduce the roots to the degree that it's almost a cutting. If you do this when it's dormant, you needn't reduce the branch structure any more than you would normally cut your trees back in the spring to increase ramification and keep them compact. OTOH, you could never do something like that to an azalea or a say, a bougie.

There are considerations to be made for the state of the plants vitality, too. You need to be much more careful about how you work on a plant that went into the fall in a weakened state. If you're talking about tropical trees as houseplants, you wouldn't want to get into the roots in the spring and do a major overhaul in the spring, when the plant is winter-stressed and at its weakest. Waiting until the month before its most robust growth, after the tree has gained some needed energy will allow a much faster recovery and less chance of complications.

Reducing the canopy commensurately with the root mass is another 'it depends' thing. If you reduce a plant that is in leaf, unless the roots are able to support the canopy with water, the tree will do a self-balancing act and shed the foliage and branching it cannot support. This can be devastating if the tree 'decides' to shed a weak branch that is an important part of your composition. The decision about whether or not to reduce the canopy must be made by the grower, based on the condition and number of fine roots you leave on the tree. There is no hard fast rule for trees in containers in this regard.

Illustration: A tree that was leftover from a workshop I put on for a bonsai club. If you could have seen it when I brought it home, you'd know why it was left over. I pruned the canopy back hard after I brought it home to try to make something of it. Here it is a year or two after the initial pruning, growing 'wild':

When I got into the roots, it looked like this:

You can see there were some severe deformities that needed correcting:

In order to do that, I had to go dangerously close to removing nearly ALL of the roots. I left only enough rootage to keep the plant alive. I made this decision based on the excellent o/a vitality and the tree's health - both were excellent:

The container was already prepared:

and the tree repotted:

Knowing that the volume of roots left on the tree would NEVER support the foliage, and left to its own devices, the tree would randomly shed large branches important to the future (composition) of the tree, I also reduced the canopy by cutting back hard:

It still needs some minor root correction (amputation, actually) but the next repot will allow me to do that easily. Also, at the next repot, I won't have to remove many fine roots at all, so after I do the root pruning, I'll probably leave the entire canopy intact until the roots have recovered and normal growth resumed. That usually takes 2-4 weeks, at which time I'll prune the canopy back as hard as necessary to ensure my visionary goals for the tree are on track.

It's good to remember that plants don't keep unnecessary parts or parts that are superfluous, they shed them. Pruning roots causes an organism-wide reaction, as does pruning the canopy. Pruning the canopy hard causes the plant to shed roots - you just can't see it happen. Pruning roots causes stress that may or may not cause shedding - that's where your judgement comes to play.

There are many different considerations pertaining to whether the plant is tropical, deciduous, a conifer ...... and the same rules and reactions that govern trees apply to houseplants that need (full) repotting regularly to maintain best vitality.

If you have specific questions about a particular plant, I can probably offer more specific detail, if you're interested.


    Bookmark   March 26, 2011 at 10:05AM
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Makes sense to me. The reason I asked was because that's what I always did, but a lot of my readings were saying that if you prune 1/3 of the roots, that 1/3 of the foliage will die off because there's not enough roots to supply water.

I guess what my goal is, is to grow plants larger, without having a huge pot. I always seem to feel the need to pot up to grow them bigger, but then I go to a greenhouse, and see one twice the size of mine, in half the pot size. Every time I go to repot, it seemed like the entire pot was filled with roots, so I'd pot up. I am however figuring out that it really isn't ALL roots, but that the roots are on the outside of the pot, and the middle is a solid, hard ball of peat. That's why I've chosen to do the 5-1-1 mix.



    Bookmark   March 26, 2011 at 10:05AM
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tapla (mid-MI z5b-6a)

With regard to your last post, Joe - repotting ensures that your plants at least have the opportunity to grow to their genetic potential within the limits of other cultural factors. Potting up, ensures that they can't. There is no noticeable difference in growth until about the time where the roots and soil mass reach a state where they can be lifted together from the pot intact. If plants are not potted up at or before that time, it is known that growth will be permanently affected. This is even true of trees eventually planted out, in the landscape. Root congestion never cures itself. Once plants have become rootbound, it takes corrective action by the grower or the plants will always be limited.

Here is a portion of a tread I posted called Trees in Containers II. You can read the whole thing, if interested, buy following the embedded link.

The timing of certain procedures is closely related to energy management, which gets too little consideration by most growers tending trees in containers. Because repotting and root pruning seem to be most misunderstood on the list of what it takes to maintain trees that will continually grow at close to their genetic potential, I will include some observations about those procedures to open the discussion.

I have spent literally thousands of hours digging around in root-balls of trees (let's allow that trees means any woody plant material with tree-like roots) - tropical/subtropical trees, temperate trees collected from the wild and temperate nursery stock. The wild collected trees are a challenge, usually for their lack of roots close to the trunk, and have stories of their own. The nursery stock is probably the closest examples to what most of your trees are like below the soil line, so I'll offer my thoughts for you to consider or discard as you find fitting.

I've purchased many trees from nurseries that have been containerized for long periods. Our bonsai club, just this summer, invited a visiting artist to conduct a workshop on mugo pines. The nursery (a huge operation) where we have our meetings happened to have purchased several thousand of the mugos somewhere around 10 - 12 years ago and they had been potted-up into continually larger containers ever since. Why relate these uninteresting snippets? In the cases of material that has been progressively potted-up only, large perennial roots occupied nearly the entire volume of the container, plant vitality was in severe decline, and soil in the original root-ball had become so hard that in some cases a chisel was required to remove it.

In plants that are potted-up, rootage becomes entangled. As root diameters increase, portions of roots constrict flow of water and nutrients through other roots, much the same as in the case of girdling or encircling roots on trees grown in-ground. The ratio of fine, feeder roots to more lignified and perennial roots becomes skewed to favor the larger, and practically speaking, useless roots.

Initial symptoms of poor root conditions are progressive diminishing of branch extension and reduced vitality. As rootage becomes continually compressed and restricted, branch extension stops and individual branches might die as water/nutrient translocation is further compromised. Foliage quality may not (important to understand) indicate the tree is struggling until the condition is severe, but if you observe your trees carefully, you will find them increasingly unable to cope with stressful conditions - too much/little water, heat, sun, etc. Trees that are operating under conditions of stress that has progressed to strain, will usually be diagnosed in the end as suffering from attack by insects or other bio-agents while the underlying cause goes unnoticed.

I want to mention that I draw distinct delineation between simply potting up and repotting. Potting up temporarily offers room for fine rootage to grow and do the necessary work of water/nutrient uptake, but these new roots soon lignify, while rootage in the old root mass continues to grow and become increasingly restrictive. The larger and larger containers required for potting-up & the difficulty in handling them also makes us increasingly reluctant to undertake even potting-up, let alone undertake the task of repotting/root-pruning which grows increasingly difficult with each up-potting.

So we are clear on terminology, potting up simply involves moving the plant with its root mass and soil intact, or nearly so, to a larger container and filling in around the root/soil mass with additional soil. Repotting, on the other hand, includes the removal of all or part of the soil and the pruning of roots, with an eye to removing the largest roots, as well as those that would be considered defective. Examples are roots that are dead, those growing back toward the center of the root mass, encircling, girdling or j-hooked roots, and otherwise damaged roots.

I often explain the effects of repotting vs potting up like this:

Let's rate growth/vitality potential on a scale of 1-10, with 10 being the best. We're going to say that trees in containers can only achieve a growth/vitality rating of 9, due to the somewhat limiting effects of container culture. Lets also imagine that for every year a tree goes w/o repotting or potting up, its measure of growth/vitality slips by 1 number, That is to say you pot a tree and the first year it grows at a level of 9, the next year, an 8, the next year a 7. Lets also imagine we're going to go 3 years between repotting or potting up.

Here's what happens to the tree you repot/root prune:
year 1: 9
year 2: 8
year 3: 7
year 1: 9
year 2: 8
year 3: 7
year 1: 9
year 2: 8
year 3: 7
You can see that a full repotting and root pruning returns the plant to its full potential within the limits of other cultural influences for as long as you care to repot/root prune.

Looking now at how woody plants respond to only potting up:
year 1: 9
year 2: 8
year 3: 7
pot up
year 1: 8
year 2: 7
year 3: 6
pot up
year 1: 7
year 2: 6
year 3: 5
pot up
year 1: 6
year 2: 5
year 3: 4
pot up
year 1: 5
year 2: 4
year 3: 3
pot up
year 1: 4
year 2: 3
year 3: 2
pot up
year 1: 3
year 2: 2
year 3: 1

This is a fairly accurate illustration of the influence tight roots have on a woody plant's growth/vitality. You might think of it for a moment in the context of the longevity of bonsai trees vs the life expectancy of most trees grown as houseplants, the difference between 4 years and 400 years, lying primarily in how the roots are treated.color>


    Bookmark   March 26, 2011 at 10:24AM
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My prized "tree" type plants are my favorite 3:

Money tree (pachira)
Dwarf variegated schefflera

My others are foliage plants, including lemon-lime dracaena, variegated snake plant (which is in need of repotting), and 2 types of algomenas, which I understand are easy to deal with.

I'll probably be repotting all of them into 5-1-1 mix, but the ones that are seeming in need of pruning are the schefflera, jade, and snake plant. The jade has some serious symptoms of hardened soil that I'll have to deal with. Thanks again.


    Bookmark   March 26, 2011 at 10:46AM
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tapla (mid-MI z5b-6a)

Actually, they will ALL respond favorably to rootwork - none are particularly sensitive. Let me know if you need 'step by step', Joe

Good luck!


    Bookmark   March 26, 2011 at 10:59AM
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greenman28 NorCal 7b/8a

Hey, Joe! You've got Al, the maestro, working with you! He's a wealth of help and information ;-)

Jades and Pachira happen to be two of my favorite plants, as well, and I've done extensive work with both.
I'll link to some past Threads for you. I would recommend a less water-retentive soil for the Jade, but the
choice is ultimately up to you.

Pachira (Money Tree) - Spring re-potting pics

And here's a Thread on a Jade that was frozen and had to be completely defoliated and root-pruned.
I put the recovering plant into a mix of Perlite, Pumice, Quartz, and Bark, and it came back strong.

Frozen Jade - back from the dead...


    Bookmark   March 26, 2011 at 1:24PM
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greenman28 NorCal 7b/8a

I almost forgot to link this Thread, Joe...
It's a great view of how drastically one can cut back Jade plants (in this case, Crassula ovata obliqua).
This plant is owned by Caudex1 (Keith), a highly respected cacti and succulent enthusiast and potter.
Notice how he removed foliage, then roots, then foliage, staggered as Al describes.

Jade-root pruning


    Bookmark   March 26, 2011 at 1:34PM
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I must say I am very grateful for this thread!

Thank you Al, Rhizzo, Josh for what you do. I keep taking in this knowledge as I prepare to root prune a tree myself for the first time.

I will be doing it on an olive tree I spared from death and to be honest, I am a bit scared. This is the kind of thread I need to keep reading to give me the courage to jump in.

Thank you so much again.

Al: What is that piece of white thing in your container? Is that a piece of yarn? Or is that a piece of rope? Where do you get that? I think I am automatically going to put wicks in many containers come my re-pots this spring.:-0)


    Bookmark   March 26, 2011 at 10:30PM
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tapla (mid-MI z5b-6a)

That is a strand from a 100% rayon mop head - what I use as a wick for new repots, even in the gritty mix. It ensures that no perched water remains in the soil. It's an extra step and a little more effort, but I don't mind going the extra mile to ensure that where the roots reside is as healthy an environment as I can make it. I think I mentioned on the container forum yesterday that a green thumb doesn't come from luck or even from experience. It comes as a result of knowing how plants work, then working hard to ensure they get what makes them work best. Paying attention to all the details, and knowing how to reduce the degree of negative influence of all potential limiting factors is what makes a green thumb.


    Bookmark   March 26, 2011 at 10:48PM
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Actually, I cut my pachira back every christmas, down to stubs off the main leader. By the end of fall, it is 6 to 7 feet tall. It gets full sun, so it does grow fast, although the reason I started cutting it back is because it drops so many leaves in the dry winters. Right now, I think it is over potted, and intend to reduce the pot size this spring, with some 5-1-1 mix. The base is about 3" thick, and I have it in a 14" pot, so as you can see, WAY overkill.

As for my jade, the one I have is a cutting of my original jade that I got 12 years ago. The original got left outside on cold night, and froze. The only part not damaged was an inside branch, so I lopped it off, rooted it, and alas, she's still with me. I know too about how drastic you can prune jades, because I once lopped the whole plant down to a 3" stub, so I could start fresh and reshape it. I didn't root prune though. The problem I've had in the past, well, bagged soil past, when using a cactus mix, is that it dried up too fast. It seems jades need a lot of water in summer when growing. Lovely plant though, because who doesn't know what a jade is?


    Bookmark   March 26, 2011 at 11:09PM
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Thanks all; I was just thinking about asking the same question, for some further clarification, but now I don't have to!

    Bookmark   March 27, 2011 at 5:20PM
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