Plants usually need an adjustment period after repots if root work was extensive. When potting up, usually there is little noticeable difference, just a temporary increase in vitality. Repot/root-pruning will cause the tree to sulk for awhile & the time period varies. (BTW, Acers tolerate total bare-rooting very well, so don't be reluctant to remove all the old soil from the root mass). Also, timing of the repot impacts recovery. Visible signs are temporary slowed or nonexistent growth, temporary loss of vitality, possible loss of some buds. I would tend to consider leaf burn a result of a root system that is yet unable to keep up with water demand put on the tree by other cultural conditions (wind, sun, high temps), or fertilizer salt issues. Also, cellular pH has the ultimate affect on color, but soil pH affects cellular pH to a certain degree. Couldn't guess at soil pH unless we know soil make-up. Do you know? I can tell you how to test container media pH if you wish to know & don't, but it will vary widely over time.

If I remember, we had some off forum discussions about soils for your Acers? Are you the one that linked me to another forum site discussion about Acer nutrient preferences? If so, I was impressed by the knowledge of the posters. I have always found that the fast soils I grow in require more N than I would at first think. However, I also know that generous applications of N in containerized Acers can bring about some unwanted problems. If you still have access to the folks you were talking to previously, I would seek nutritional advice from them. That works for me doesn't mean it will work for you.

Are you the one who spoke of adding some extremely large pine bark to the mix? Is it possible the soil is simply becoming to dry between irrigating? What else is in the soil aside from the bark?

Pam comes here often - also grows lots of Acers in containers. Perhaps she will read & offer her advice, which is always sterling. I'm at work now, but I'll link her to this tonight.

Al

Hello, Al-
yes, that was me. I repotted after a year only, but no rootpruning seemed necessary since the containers are pretty large (25+gallons). The roots had entered all parts of the pots but there was still plenty of room to grow, so I eliminated as much as possible (most of) the old soil and planted in a mix that has about 40% bark (1/3 - 1 inch size, plus some larger size mixed in) as well as another 20% similar sized clay pellets, as well as a mostly peatless mix that uses cocomaterial (fiber, some cocopeat), wood chaff, and some composted bark. I added very little fertilizer (none for some 2 year old maples) after the recommendations you are referring to.

As regards any more fertilization (if at all necessary) I intend to wait another 2-3 weeks until the leaves are all out.

Does the soil become too dry? I can't be sure as this is a totally new mix, but don't think so, since rainfall was decent and I watered. But I still am not familiar with the particularities of the mix.
The weather - possible. There was good sunshine as they were leafing out, and a sudden drop in temperature to around freezing for a few nights, and then again a rise to near summer temps.
The PH should be below 7, since besides the bark and the clay, the mix has a PH around 6.
Yes, if you could tell me about how to measure PH, that would be great.

Finally, as regards the pretty large pine bark pieces: I spoke to two of the bigger acer growers in Europe: they both spoke of using pretty big bark pieces (1 and 1/2 inches+), half mixed in with my initial soil. I stayed conservative as regards that: in general I stuck to the size your photo with the 25 cent coin shows.

So in other words; you say rootpruning can have a visible effect for a while, whereas just repotting doesn't have much effect except increased vitality.

And that the fact that I repot in a totally new mix shouldn't affect response, if the mix itself is good?

Thanks; Al, for replying even from work. Have a good day.

On the root-pruning. The key word was a "temporary" increase in vitality. A properly root-pruned tree will catch and pass a potted-up tree, usually by the middle of summer. In most instances, biomass produced above ground will be noticeably greater in the root-pruned tree.

It is important to longevity that old soil is eventually removed from your roots. It hardens, restricts water/nutrient transport, and causes death of individual branches, especially in trees that don't move water laterally (circumferentially) through the xylem well (Acer, Prunus, Buxus, Thuja, others).

Can't really say how your trees should respond to the mix you are using. It sounds reasonable, and like it should hold moisture well. We've probably discussed this, but FWIW, I use a 2/3 inorganic mix for Acers. Wonder what the salt content of the coco-products in the soil was? It has been a problem for some.

To test container media pH: Saturate soil thoroughly with distilled water. Water a second time so some water escapes from drain hole. Wait 1 hour. Water soil surface again and collect about 1 oz of water that first escapes from drain hole. The pH of this water is your media pH.

Al

Hi, Al-

thanks for the info on soil PH.

Yes on removing all the old soil: I think I got rid of most, especially since I used an all-new soil. I should be able to remove the rest, if there is some next time.

The salt content (and the initial fertilization) of the mix containing coco products was really low - one reason why I got the mix. It is specially prepared by the company, usually reserved for growers who want to control how they grow their plants, and contains little peat. I had also discussed the mix with a German maple grower who uses it.

I know your mix: I want to try it on some of my plants, - right now, getting the ingredients (the equivalent of turface, chicken grit) is difficult. (The chicken grit is here calcium carbonate, and the pieces are too small. Smaller chicken?) Plus: during the week my father needs to water the many trees, as I work elsewhere, which means I need a safety net as regards moisture...

So, if the mix is good, radically changing the soil should not affect the trees.

Thanks for your response.

So, if the mix is good, radically changing the soil should not affect the trees?

I would say true. I have root-pruned & repotted many hundreds of plants from the nursery soil they arrived in, or from in situ situations (collected from wild) and never had issues come up with soil choice. It's difficult to get a plant to grow more robustly in a container than where it occurs naturally, so I won't lay claim to better growth in these trees, but in all cases, I saw improvement in container grown material as soon as the plant adjusted after the work.

Al