We have a beautiful and healthy Bay Laurel tree about 7 feet tall. It's been in the same 22" diameter concrete container for well over six years. Surely it is root bound by now?

So why does it look so healthy? Yes, I keep it well hydrated, feed it often with vermicompost tea and give it a shot of Miracle Grow once a year.

I am afraid to repot it. It is way too heavy for me to handle. Large pots are hard to find, not to mention pricey. And the tree looks so healthy!

Is it possible the species tolerates being root bound?

What do you know?
PotterK

You are giving it all the nutrients it needs in the tea, so it doesn't matter particularly how the roots are growing. The problem with rootbound trees is when they get planted in the ground and can't straighten those twisted roots so they eventually choke the tree. In containers that isn't a problem for years and years. There will come a time way down the road when there are so many roots that there isn't enough soil to hold moisture and nutrients.
What you would have to do is remove the plant from the pot and remove a bunch of soil and roots like a giant bonsai. If it's a Grecian Bay, the kind that you use for seasoning, it will handle it fine. A true California Bay Laurel, Umbellularia californica, is more sensitive and will need more careful treatment. This is their growing season so now is a decent time to try.

Thanks.
I don't think of this as a problem. Trees come and go.

And if it ain't broke, don't fix it. If it is broke, try something different.

My question is mostly theoretical: about the physiology of root boundedness. Why some plants can tolerate it while others can not.
You say the soil disappears and the root volume will fill the pot. New roots keep growing but have nowhere to go. But they can still function (take up nutrients and water)?
We have a jade plant that was in the same pot for over 30 years. I took it out to repot, only to find it was not root bound at all. Its roots weren't even cramped! Do they self-thin, or what?
PotterK

Jade plants have a very fine fibrous root system that doesn't squeeze itself out. The roots of woody plants continue to get thicker and thicker and can literally cut the trunk at the base and kill the plant. Grasses and other monocots have roots that never increase in diameter so they don't get rootbound.
Yes, the roots can still function as long as they can continue to create root hairs at the tip of the root which is where all the absorbing occurs.

Ah!
Thanks CPgardener.

One other question, CPgardener, if I may:
You say a tree's roots in a container will grow to the point where "... there will be too many roots and not enough soil ..." I have heard that from other sources, too; that over time the soil in a container will disappear.

What actually, physically, happens to the soil matter? Does the tree incorporate it into its own tissue? Do soil organisms metabolize it away? How can soil disappear like that?

PotterK

The organic matter decomposes and the inorganic gets washed out the bottom or off the top. There will still be some within the mass of roots but most will disappear.

@greenriverfs What actually, physically, happens to the soil matter? OM in substrates is composed of hydrocarbon chains which contain hydrogen, carbon, oxygen, and an assortment of other elements, many of which are nutrients. As the hydrocarbon chains of OM are cleaved by soil organisms, the nutrients become available in an ionic form plants can assimilate and use as a) the building blocks for new growth, and b) to keep the plant's systems and cycles balanced and operating as designed by Mother Nature. The carbon and oxygen from cleaved hydrocarbon chains gasses off as CO2 efflux.

Shorter version: container substrate shrinkage unrelated to water absorption and loss is almost entirely due to the carbon and oxygen in hydrocarbon chains gassing off as CO2.

Surely it is root bound by now? So why does it look so healthy? Appearances can be very deceiving when it comes to gauging a plant's health, and equally or more important, how much of it's genetic potential is being realized and what % of that potential is left lying on the table as a result of root congestion. A plant can be realizing only 1/3 or so of it's genetic potential in terms of growth rate, vitality level (health), its ability to defend itself against insect herbivory as well as disease pathogens, and eye appeal. Here is something I wrote about the fallacy that some plants like or prefer to be grown under rootbound conditions. Tight roots creates stress and stress is always a negative when looking at things from the plant's perspective.

Myth: This Plant Likes/Prefers to be Root-Bound
tapla (mid-Michigan, USDA z5b-6a)14 years ago

I would like to talk a little about, and hopefully dispel the myth that certain plants 'like' or 'prefer' to be grown tight (under root-bound conditions). Maybe we can also understand that no plant will 'do well' when it's pot-bound if you are using a plant with plenty of room for its roots as your standard of judgment. If plants did better growing under root-bound conditions, it would seem that Mother Nature would have arranged for in situ (where they naturally occur) plants to grow with their roots in tight little cones or cubes, yet we never see that occur. While it's true that we may be able to use the STRESS of our plants being root-bound to bend plants to our will and achieve OUR goals, the fact is that this serves US well, and not the plant.

Lets examine what 'growth' is. Growth is simply a measure of the increase in a plant's biomass, how much bigger it has become (the weight of the sum of it's parts), and is the actual measure of how 'well' a plant is doing. We know that tight roots restrict growth, reduce the amount of extension, and reduce the potential for an increase in mass, so even if we THINK plants are doing well because we use the stress of tight roots to get them to bloom or grow in a particular habit that we like, the truth is tight roots are stressful and plants would rather have plenty of room for their roots to grow so they could grow as mother nature intended. No one is more aware of the negative influence tight roots has on growth than the bonsai practitioner who uses that tool extensively to bind down the plant's growth habits so the will of the grower, not the plant, prevails. Using tight roots as a tool to achieve an end is all about the grower's wants, and not the plant's.

If we chase this a little further, we can see the reasons that it is suggested that particular plants might like root-bound conditions. Tight roots alters the plant's growth habits and the stress of tight roots can cause other physiological responses like bloom induction. Again, this is happening because of stress, and is the plants unhappy response. Bright flowers make the grower happy, but the plant's perspective may be entirely different.

Where I was really heading when I started to write this is: There is a relationship between plant mass (size), the physical characteristics of the soil, and the size of the container. In many cases, when we are advised that 'X' plant prefers to be grown tight, we are being told that this plant won't tolerate wet feet for extended periods. Someone somewhere assumed that we would be growing this plant in an out-of-the-bag, water retentive soil, and "a big pot o' that soil stays wet for a long time, so we better tell these people to grow this plant in a tiny pot so the plant can use the water in the soil quicker; then, air will return to the soil faster and roots won't rot.

If you place a plant in a gallon of water-retentive soil, it might use the water fairly quickly, at least quickly enough to prevent root rot; but if you put the same plant in 5 gallons of water-retentive soil, the plant will take 5 times as long to use the water and for air to return to the soil, making it much more probable that root rot issues will arise. So lets tell 'em to grow these plants tight to save them (the growers) from themselves ......... because we KNOW they're all going to be using a soggy soil.

Key here, is the soil. If you choose a very porous soil that drains well and supports no (or very little) perched water (that water in the saturated layer of soil at the bottom of the pot), you can grow a very small plant in a very large pot and make the plant MUCH happier than if you were growing it tight. You still have the option of choosing those plants you prefer to stress intentionally (with tight roots) to get them to grow as YOU please, but for the others, which comprise the highest %, it makes much better sense to change to a soil that allows you to give the plant what it wants than to stress the plant so it won't die. That's a little like keeping your dog in a sleeping bag 24-7 to ensure he doesn't get cold.

***********************************************************

Tight roots and a decreasing volume of soil due to gassing off act in conjunction to limit the volume of soil which limits the availability of essential resources, water, air, nutrients. A growing plant with it's growing root mass + a shrinking soil mass is never a good idea when viewed from the plant's perspective.

I also sent you a link to the entire thread, which includes commentary by a friend, the late Steve Lucas, formerly of Exotic Rain Forest.

Al

That is an enlightening explanation, Al. I thank you.

One question: CalPolygardener stated (above, in this thread) that the roots of grasses and other monocots don't increase in diameter, so they don't get root bound. If that is true, does it mean the old roots of a monocot die off over time and get replaced by younger roots of similar diameter? I imagine the dead roots decomposing and providing organic matter to the site. A sort of self fertilization scheme. Self-canabilism? If so, then conceivably grasses and monocots could be said to tolerate root boundedness (not implying they actually LIKE it) better than plants of other physiology. What's your take on that?

PotterK

Yes, at least in containers that's what happens. They tolerate it much better than dicots like oaks, ficus, bay trees and other dicots.
The root cores are made of lots of lignin which decomposes very slowly. The softer parts on the outside of the roots decompose fairly fast, while the hard center takes years to. The pot does end up with a lot of those dead roots eventually and that does leave less room for new ones. All those roots taking their time to decompose makes grasslands a great carbon sink; lawns too.
And yes, the new roots are pretty much the same diameter as the old roots. If you dig down in a well-established lawn and a fairly new one you will see that the roots in both all look the same size. It's even easier to see in container-grown palms, monsteras, aloes and other large monocots.

Any plant growing under rootbound conditions suffers a degree of lost potential roughly commensurate to how serious the congestion is. As the congestion increases, so do the congestion's limiting effects.

I've grown a LOT of grasses and various other monocots long term as companion plants to bonsai on display, and can say with absolute certainty that grasses and other monocots grown under conventional container culture are not exempt from the effects of tight roots. They are as affected by root congestion as both woody and herbaceous dicots.

Even if we were to allow that roots of monocots don't increase in diameter (I question that idea), we know with absolute certainty that they do multiply and fill containers the the degree access to resources is limited both by the increasing volume of roots and by the decrease in available oxygen. When I repot plantings of grasses or other monocots to relieve root congestion, It's typically because growth has nearly stopped or stopped altogether. After removing most of the roots from the bottom of the root/soil mass so the remaining root mass is about 1/2" thick, and repotting into fresh soil, the increase in growth rate, vitality, and the increase in stems is very conspicuous. The increase in growth rate, vitality, the plant's ability to defend itself, and typically - eye appeal, should not be seen as a growth spurt. In fact, it is a clear indication of how serious the limitations associated with the root congestion actually were. The plant could have and would have been enjoying the "new and improved" increase in growth and function all along had the plant been repotted at appropriate intervals rather than being left to suffer the effects of root congestion.

Al

Thank you both.

I am reminded of the statement by my silviculturist friend: "Sure, sub-alpine firs grow in the most inhospitable of places - heavy snow bearing down, extreme cold, short seasons - but that doesn't mean they won't thrive at lower (more benign) elevations."

As a container gardener interested in the aesthetics (and not so much in the comfort of the plant) it's useful knowing which kinds can best tolerate my abuse!

PotterK

Monocots, mostly, don't have a cambium layer like dicots do. Once a stem hardens it stops growing in diameter. Look at palms and you will see that 60' ones have the same trunk diameters as 20' ones. Same with bamboos and the culms don't get any thicker once they harden. The roots grow the same way. There are vascular bundles that move water and nutrients around the plant surrounded by ground tissue wrapped in epidermal tissue. They get longer but don't get thicker.
If you up-pot a pot bound grass without doing the root trimming, it will respond the same as one that is trimmed and repotted only faster since there is no root damage.

So the elements that make up the dead and rotting root become available to the plant again via the new roots? A recycling of the N, etc., like a tree recycles the N in its leaves before dropping them?

Understandably, as any plant increases in mass it develops a more massive root systems. But monocots shed old roots as part of the process?

In both cases, then, root boundedness stresses the plant (Al's point), but in subtly different ways (CP's point).

Fascinating, no?

"Sure, sub-alpine firs grow in the most inhospitable of places - heavy snow bearing down, extreme cold, short seasons - but that doesn't mean they won't thrive at lower (more benign) elevations." Many people err in the belief that since a plant lives in a riparian setting it should tolerate living in a container and be able to deal with the transition from boggy to more favorable air/moisture levels and back again. It won't. In order for a terrestrial plant to survive long term, the root pith tissue must undergo a transition from the normal parenchymous tissue to another type of tissue (aerenchymous), which has longitudinal air spaces that allow diffusion of air through stem tissue into roots, which provides the oxygen needed to drive root metabolic functions.

Too, it is extremely common for plants to be found more often in settings considered marginal insofar as the plant's ability to tolerate the site. This is because vigor is a genetic trait and a more vigorous plant can and often does out-compete less vigorous plants for the choice real estate.

As a container gardener interested in the aesthetics (and not so much in the comfort of the plant) it's useful knowing which kinds can best tolerate my abuse! My focus is primarily on bonsai, but experienced bonsai practitioners often grow plants for several years in the ground before moving them to a large container to begin basic training. It's not uncommon for a tree to live 5 years or more in the ground, another 5 years or more in a large container, then an indefinite period in a bonsai pot where it undergoes continuous refinement. One learns quickly how to deal with the stress of regular refinement and living in a container. The number one contributor to retarded development is root congestion, which is why, if you want a highly refined tree within the span of 1-2 decades, root congestion needs to be relieved through repotting regularly. Most young trees get repotted annually or every other year. Trees older than 25-30 years are generally repotted less often, but that depends on how aggressive their root systems are.

Most young potted trees, regardless of how large the pot is, will begin suffering from root congestion by the end of their first year in the pot. By the end of the second year, the limitations become conspicuous if you look for them, even though the tree might look perfectly healthy. Root congestion can/does rob plants of a very large fraction of growth, vitality, ability to defend itself, and often eye appeal. There are 2 problems with lost potential other than it's effect on the plant. 1) It isn't always detectable until it is robbing your plant of 75% or more of it's growth/health potential, and 2) lost potential can never be regained.

Al