Sigh! - I had the whole answer all typed out & something in my 'puter ate it!

. . . should I include the soil the trees came in, in to the new containers, or would that largely defeat the whole purpose of your mix?

You'll need to remove it to care for the roots appropriately if your aim is long term vitality in your containerized woody plants. In the case of material that has been progressively potted-up, large perennial roots can occupy nearly the entire volume of the container, causing plant decline. Soil in the original root-ball can actually become so hard that in some cases that a chisel may required to remove it. I've witnessed this many times in trees that have been potted-up for periods as short as 6 or 7 years.

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 lessened vitality. As rootage becomes continually compressed and restricted, branch extension stops and individual branches die as water/nutrient translocation is further compromised. Foliage quality may not 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.

Potting-up temporarily offers room for fine rootage to do the necessary work of water/nutrient uptake, but these roots also soon lignify while rootage in the old root mass continues to grow and become increasingly restricted. The larger and larger containers required for potting-up & the difficulty in handling them also makes us increasingly reluctant to undertake even potting-up.

I haven't yet mentioned that the dissimilar characteristics of the old soil as compared to the new soil when potting-up are also a recipe for trouble. With a compacted soil in the old roots and a fresh batch of soil surrounding the roots of a freshly potted-up tree, it's impossible to establish a watering regimen that doesn't keep the differing soils either too wet or too dry, both conditions occurring concurrently being the rule rather than the exception.

. . . do you have any theories as to why the nurseries don't use a variation of your mix for their containers, and instead use rich organic matter for their containers. . . . what is it that leads you to the conclusion that your mix is better suited for containers than the rich organic matter that the nurseries use?

First, I primarily make the conclusion based on years of experience and comparison, but also on the application of simple soil science. Most of the plants I own were once in nursery soil. The increase in vitality and ease of maintaining them after repotting into my choice of soil is readily apparent time after time in all the woody material.

The focus of nursery operations is on profit, and a salable tree is how they realize a profit. After the tree leaves the nursery, they care not a whit about what happens to it. Your/my focus isn't on profit, but on healthy trees.

Bark and peat are much less expensive than Turface and granite, so the nurseries opt for the least expensive ingredients that will get a plant to market in salable condition - economics. Additionally, it takes time to water plants, so they choose to grow in as water retentive mix as they can that will still maintain adequate aeration until the plant is sold.

These are a large part of the picture, but I'm certain there are other points, both major and fine that I omitted. I hope I've explained my reasoning adequately.

Al

also Al, do you have any theories as to why the nurseries dont use a variation of your mix for their containers,

I waited for Al to give his response before posting this as I didn't want to be a distraction.

Where I live there is a very large, family owned nursery that in many respects is excellent. When I went to find a source of bark fines I went there right off the bat. When I didn't find what I was looking for I spoke to an employee who said she didn't think they had what I was looking for, but would get the ordering manager to talk with me to see if they could get it.

I spoke with the manager trying to explain what pine bark fines were and she just wasn't understanding. I walked over to where some containerized plants were on display, grabbed a small handful of the mix and said 'This is what i want.' pointing to the bark pieces.

She then went on to explain they didn't have any of that. 100% of their plants came in the mix the supplier provided. They just happen to have a decent supplier who uses a good mix.

I mention this both because I think it is a kind of cute story, but also to underscore Al's point that nurseries are all about getting you a product you will buy and there is no reason for them to spend more money on growing media than they have to in order to get you to buy the plant.

This isn't to say there are no nurseries out there that would like us to have good success with plants, just that they don't put plants into a mix they expect it to be in longer than it takes to sell us the plant.

many thanks for your responses. very helpful.

Al, I assume you welcome and encourage polite scientific inquiry into your theories.

Lolol - sure, any time. Why do you call them 'theories'? ;o)

Al

I'd like to chime in on the nursery potting media issue if I may. Since I've worked both for retail nurseries and wholesale growers, I think I've got a reasonable understanding of their methodology and why they do what they do. Obviously I can't speak for all of them, but I have to think that most larger, well-established and reputable operations will have the same philosophy.

There is a great deal of study by nurserymen and wholesale growers as to what constitutes the best soil (or soil-less) mix for their containerized plants. And their requirements do not necessarily match ours as home container gardeners. Drainage is always a key component as watering and fertigation is frequent, maybe even more so than it is for home gardeners. But the mix is not intended for long term purposes. It is intended to provide support - physical, and to a lesser extent, nutritional - for the anticipated short time it takes to grow on the plant for sale and market it to either the retailer or directly to the consumer. And depending on the crop, this may involve several potting ups to larger sized containers in the course of a single season. So the amount of organic matter contained in the mix is not necessarily at issue, as the plant is not intended to live in the soil any longer than the few weeks to a few months it takes to repot OR deliver it to the purchaser. Yes, it does offer perhaps greater moisture retention than is ideal in a home container situation, but that's also part of the intent as containerized plants in a retail nursery setting dry out extremely quickly. Situations which require a longer holding period generally have a soil mix that supports that longer term, with bark products a much higher percentage of the mix, much like Al's.

So it's a matter of both efficiency in production and maintenance and bringing on a plant quickly in terms of both growth and appearance for a fast sell. Of course profits are a motive - no nursery could stay in business if this was not a high priority concern - but unhealthy and wimpy looking plants will impact the bottom line just as rapidly.