What is more important when potting up, width or depth?

Randers, Denmark

I am to potting many of plants up in larger pots. I've got some a few pots which are twice as deep as the ones I need to pot up, but maybe only an inch wider?

So, what is more important, depth or width?

Bay City, MI(Zone 6a)

Both are important because they have a direct relationship to volume, but deep pots are easier to grow in and more forgiving than shallow pots. Given 2 pots that each hold 5 L of soil, one deep the other shallow, the deeper pot offers a wider margin for grower error when it comes to watering habits, and greater potential for plants to grow nearer to their potential.

You're aware that there is a considerable difference between potting up and repotting, with potting up contrasting sharply with repotting because the former ensures limitations?

Al

Randers, Denmark

Nah, I have a hard time really understanding the difference. With many of my plants, I can see the root system coming out of the bottom. I just want to give those plants bigger pots and hopefully some better soil...a mix of normal soil in a bag, blend with perlite and bark.

Bay City, MI(Zone 6a)

Copy/pasted from the sticky thread at the top of this forum:

As noted above, most growers draw no distinction between ‘repotting’ and ‘potting up’. I have spent literally thousands of hours digging around in the root-balls of containerized plants. Old plants from nurseries of greenhouses are probably the closest examples to what most houseplants are like below the soil line, so I'll offer my thoughts for you to consider or discard as you find fitting.

I have helped salvage many plants that had been containerized for long periods and were ‘circling the drain’. Not long ago, our bonsai club 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 the roots constrict other roots and impair the flow of water and nutrients through them, much the same as in the case of girdling or encircling roots on perennials grown in-ground. The ratio of fine, feeder roots to more lignified (woody) and perennial roots becomes skewed to favor the larger, and practically speaking, useless roots.

The initial symptoms of poor root conditions are progressive diminishing of branch extension on plants that branch, loss/shedding of foliage on the parts of branches nearest to the ‘trunk’, often giving the plant a ‘poodle look’, and reduced vitality. As rootage becomes continually compressed and restricted, branch extension stops and individual branches might die as water/nutrient movement 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 plants 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/disease while the underlying cause goes unnoticed.

I will mention again 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:
I will rate growth/vitality potential on a scale of 1-10, with 10 being the best. We're going to say that plants 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 plant goes w/o repotting or potting up, its measure of growth/vitality slips by 1 number, That is to say you pot a plant and the first year it grows at a level of 9, the next year, an 8, the next year a 7. Also imagine please, we're going to go 3 years between repotting or potting up.

Here's what happens to the plant you repot/root prune:
year 1: 9
year 2: 8
year 3: 7
repot
year 1: 9
year 2: 8
year 3: 7
repot
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 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, or the difference between less than 4 years versus more than 400 years, lying primarily in how the roots are treated.

Al


Randers, Denmark

Oh, ok. Thanks...But I'm quite hesitant to cut off roots of my plants, I'm so afraid I will kill. Many of my plants are plants I like very much.

I'm actually quite nervous to just add bark and perlite to the soil, I've never done that either.

But as I can see, pruning of the roots seems quite important for the plants grow potential, but as I said, I have never done it before and I would hate it if I do something wrong.

Should I just go ahead and do it anyway?

This message was edited Apr 21, 2012 2:20 AM

Bay City, MI(Zone 6a)

It's always your call. I maintain hundreds of plants in containers, the largest fraction being bonsai, but there are a significant number of succulents and houseplants in that number too. Root work and full repots are a part of maintaining every plant I own; this, because I recognize and see the limiting effects of potting up on plants. There are even some plants that exhibit an indelible story that offers witness to each time they were potted up. I have a Madagascar palm that is interesting. The trunk of the plant is covered in long thorns. By the vertical distance between the thorns, you can see exactly when the plant was repotted because the plant stretches out and grows very well after a repot. The thorns then get progressively closer together each growing season until the next repot when it stretches out again. If I had been only potting up, I would have the scenario of increasing limitations on growth as illustrated in the example in my post above. I can 'read' the same information in/on trees by observing the increased/decreasing distances between leaf bundle scars, and can tell you how long it's been since your tree was last repotted or potted up, just by looking at it.

This was written to be included in a thread about containerized trees, but 99% of the information can be applied to houseplants. Just imagine 'houseplant(s) wherever you see the word tree(s).

Now that I have made the case for why it is important to regularly perform full repots (not to be confused with potting-up) and prune the roots of your containerized trees regularly, I will offer some direction. Root-pruning is the systematic removal of the largest roots in the container with emphasis on removal of rootage growing directly under the trunk and at the perimeter of the root mass.

Root pruning can start immediately with year-old seedlings by removing the taproot just below the basal flare of dormant material, repotting, and treating the plant as a cutting. This will produce a plant with flat rootage that radiates outward from the base and that will be easy to care for in the future.

Young trees (under 10 yrs old) are nearly all dynamic mass and will tolerate root-pruning well. Most deciduous trees are extremely tolerant of root work. Acer buergerianum (trident maple) is routinely reduced to a main trunk with roots pruned all the way back to the basal flare and responds to the treatment with a fresh growth of fine, fibrous roots and a fresh flush of foliage each spring. The point here is, you don't need to be concerned about the pruning if you follow a few simple guidelines.

First, some generalities: undertake repotting of most deciduous material while the plant is quiescent (this is the period after the tree has met its chill requirement and has been released from dormancy, but has not begun to grow yet because of low soil temps). Most conifers are best repotted soon after the onset of spring growth. Most tropical and subtropical trees are best repotted in the month prior to their most robust growth period (summer). Citrus are probably best repotted in spring, but they can also be repotted successfully immediately after a push of top growth.

For most plants that have not been root-pruned before: With a pruning saw, saw off the bottom 1/3 of the root ball. With a hand-rake (like you use for scratching in the garden soil) and/or a wooden chopstick and/or the aid of water under high pressure from a garden hose, remove all the loose soil. Using a jet of water from the hose and the chopstick, remove the remaining soil - ALL of it. The exception here would be those plants that form dense mats of fine roots (citrus, bougainvillea, rhododendron ...). This should be done out of sun and wind to prevent the fine roots from drying. 5 minutes in the sun or wind can kill fine roots & set the tree back a week or more, so keep roots moist by misting very frequently or dipping the roots in a tub of water as you work. After the soil is removed, remove up to another 1/3 of the remaining mass of roots with a sharp pruning tool, taking the largest roots, and those roots growing directly under the trunk. Stop your pruning cuts just beyond where a smaller root branches toward the outside of the root you are pruning. Be sure to remove any J-hooked roots, encircling/girdling roots or others exhibiting abnormal growth.

Before you begin the pruning operation, be sure you have the soil & new container ready to go (drain screens in place, etc). The tree should fit loosely inside the walls of the container. Fill the container with soil to the desired ht, mounded in the center, & place tree on the mound. Add soil to cover roots & with a chopstick/skewer, or sharpened wood dowel, work soil into all voids in the roots, eliminating the air pockets and adding soil to the bottom of the basal root-flare. Temporarily securing the tree to the container with twine or small rope, even staking, against movement from wind or being jostled will fractionalize recovery time by helping to prevent breakage of newly-formed fine rootage. Place the tree in shade & out of wind until it leafs out and re-establishes in the container.

The first time you root-prune a tree will be the most difficult & will likely take up to an hour from start to finish, unless the tree is in larger than a 5 gallon container. When you're satisfied with the work, repot into a soil that you are certain will retain its structure until the next root-pruning/repot. Tree (genetic) vigor will dictate the length of time between repots. The slow growing, less vigorous species, and older trees will likely go 5 years between repots. For these slow growing trees, it is extremely important that soils retain aeration. For these trees, a soil of 2/3 inorganic parts and 1/3 organic (I prefer pine or fir bark) is a good choice. The more vigorous plants that will only go 2 years between repots can be planted in a soil with a higher organic component if you wish, but would still benefit from the 2/3 inorganic mix.

Most trees treated this way will fully recover within about 4 weeks after the repot By the end of 8 weeks, they will normally have caught & passed, in both development and in vitality, a similar root-bound plant that was only potted up

When root-pruning a quiescent plant, you needn't worry much about "balancing" top growth with rootage removed. The plant will tend to only "activate" the buds it can supply with water. It is, however, the optimum time to undertake any pruning you may wish to attend to.

This is how I treat most of my trees. Though I have many growing in bonsai pots, more of my plants are in nursery containers or terra-cotta and look very much like your trees, as they await the beginning of intensive training. With a little effort at developing a soil from what's available to you and some knowledge and application of root-pruning and repotting techniques, I'm absolutely sure that a good % of those nurturing trees in containers could look forward to results they can be very pleased with. This is the repotting technique described that allows bonsai trees to live for hundreds of years & be passed from generation to generation while other containerized trees that have not had their roots tended to, and have only been potted-up, are likely to be in severe decline, or compost, well before they're old enough to vote. ;o)

I hope you're bold enough to make it a part of your containerized tree maintenance, and I hope what I've written so far makes sense. Thank you so much for your interest.


Al



Palm Bay, FL(Zone 9b)

I got a couple of cents to toss in regarding depth and width...

Generally, if I have a plant that doesn't get too big very quickly, and is fairly drought tolerant, I feel safe planting it in a shallower depth pot. Cacti and succulents don't seem to need deep soil (more than 6" or 15cm) unless they've gotten over a foot (30cm) tall.

As far as width is concerned, unless you're making multiple plantings in one pot, the width of the pot shouldn't be more than half the width of the plant's foliage spread. If the width is too much, it won't really help the plant - and you have more soil surface that can collect weeds.

Biggest thing to consider when re-potting is making sure the soil is deep enough to accommodate the plant's needs, but you can still leave at least an inch between the top of the soil and the top of the pot so you can give it a good drink when it needs it.

Bay City, MI(Zone 6a)

Cacti and succulents are much more difficult in shallow pots unless the soil is comprised entirely of large particles, and soil volume is much more important than pot dimensions. Still, deeper pots are easier to grow in and more forgiving of watering errors. The larger the container, the faster the growth, all other considerations being equal. Unfortunately, many of you are using soils that limit your ability to take advantage of the increased growth larger soil volumes offer because your soil would remain wet for so long it would affect root health/function. Best is to use a soil that allows you to ignore pot size - one that carries with it no danger of 'over-potting' - even in shallow containers where the risk is increased. Along with that choice comes not only the opportunity for better growth and vitality, but a much wider margin for grower error as well.

Al

Thumbnail by tapla
Randers, Denmark

Well, about the soil, I have kinda given up on following your recipes because it's hard to translate some of the stuff to danish products.

What I have done is added A LOT of bark and perlite to the normal soil you can buy in a bag. Maybe half soil half bark and 25% perlite.

I hope it won't kill my plants.

Bay City, MI(Zone 6a)

You might forget the recipes & still be able to embrace the concept, which it seems you're trying to do. The recipes are simply the best ways I've found to implement the concept, and aren't offered as the ONLY way. I'm guessing you might have a lot of spruce bark available where you live. If so, keep on the lookout for spruce or pine bark with particles mostly under 8mm. From that, it's easy to get to a 5:1:1 ratio of bark:perlite:your potting soil. The only other thing you would need to add would be a little dolomitic lime (garden lime that contains Ca and Mg).

Al

Quote from tapla :
Copy/pasted from the sticky thread at the top of this forum:

As noted above, most growers draw no distinction between ‘repotting’ and ‘potting up’. I have spent literally thousands of hours digging around in the root-balls of containerized plants. Old plants from nurseries of greenhouses are probably the closest examples to what most houseplants are like below the soil line, so I'll offer my thoughts for you to consider or discard as you find fitting.

I have helped salvage many plants that had been containerized for long periods and were ‘circling the drain’. Not long ago, our bonsai club 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 the roots constrict other roots and impair the flow of water and nutrients through them, much the same as in the case of girdling or encircling roots on perennials grown in-ground. The ratio of fine, feeder roots to more lignified (woody) and perennial roots becomes skewed to favor the larger, and practically speaking, useless roots.

The initial symptoms of poor root conditions are progressive diminishing of branch extension on plants that branch, loss/shedding of foliage on the parts of branches nearest to the ‘trunk’, often giving the plant a ‘poodle look’, and reduced vitality. As rootage becomes continually compressed and restricted, branch extension stops and individual branches might die as water/nutrient movement 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 plants 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/disease while the underlying cause goes unnoticed.

I will mention again 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:
I will rate growth/vitality potential on a scale of 1-10, with 10 being the best. We're going to say that plants 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 plant goes w/o repotting or potting up, its measure of growth/vitality slips by 1 number, That is to say you pot a plant and the first year it grows at a level of 9, the next year, an 8, the next year a 7. Also imagine please, we're going to go 3 years between repotting or potting up.

Here's what happens to the plant you repot/root prune:
year 1: 9
year 2: 8
year 3: 7
repot
year 1: 9
year 2: 8
year 3: 7
repot
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 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, or the difference between less than 4 years versus more than 400 years, lying primarily in how the roots are treated.

Al




Hi, Al. This is the most helpful post I've ever seen on this subject. Thank you so much for taking the time to bring this information to us. I actually had read this post years ago (stumbled upon it through a Google search), and have been utilising the information with my own container plants. But I never bookmarked it after I first read it, so i was happy to see it here again (now bookmarked and printed!).

I was wondering your opinion of those air-pruning pots. They seem to have the same end effect as your instructions above have on a plant's root system. I am wanting to grow some big trees in pots, but I'm not so young and strong now as I was when a little younger (and perhaps I'm also a little lazier!), so l was thinking the air-pruning pots for the very large trees would require a little less work less often. What are your thoughts?

Thanks again for that (as far as I'm concerned) historic and epic post!

Michaela

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