Just purchased Japanese maples, when to repot?

13 years ago

I recently bought several Acer Palmatum: Sango Kaku, Waterfall, and Shishigashira. They came in 1 gallon pots averaging about 2-3 feet.

I would like to repot them with Al's 5-1-1 mixture because of the positive responses.

After researching the forum, I am still not clear if it's okay to repot them or not. I'm concerned because Spring is ending and the temperature has been rising. Will they be okay if I repot them now or should I wait for a better time?

Thank you for your help.

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tapla (mid-Michigan, USDA z5b-6a)

13 years ago

last modified: 8 years ago

I successfully tend to some 200 containerized trees that are in various stages of development for bonsai, many are Acers. I lecture regularly by invitation on container culture in general, and many other tree-related subjects. My next presentation is Wed, May 6, to the Gladwin County, MI Master Gardeners.

The above-ground portion of trees are able to tolerate much colder temperatures than roots. 14* is considered the industry standard for killing low for mature rootage on A palmatum, so it's inaccurate to say that roots are fine above 15* soil temps and in jeopardy at temperatures below 15*. Succulent rootage and hair roots are often unable to tolerate temperatures only slightly below freezing. As temperatures fall, larger and more lignified roots succumb to the cold. As stated above - all roots on a plant are not created equal when it comes to cold tolerance.

12-24 inch (deep) soil temperatures rarely see temperatures drop much below 25*, but the top 6" of soil, where the bulk of our containerized tree's roots are - does get extremely cold - certainly well below killing lows for fine rootage (though perhaps not for larger roots).

I could site Dr. Whitcomb for support, but I'll let you look at his text at your leisure, since it appears you have it. Note Chapter 13, pages 308 -338 to see that what I'm saying is not only logical, but it's supported abundantly in his work as well as a plethora of other literature.

Something I wrote previously: "Commonly, each species of plant has a general range of cold-hardiness. Within species and cultivar, cold-hardiness is genetically determined. That is to say that a plant that is propagated from cuttings or tissue culture will have the same ability to resist cold as the parent plant. Plants cannot "develop" a greater degree of cold-hardiness by repeated or prolonged exposure to cold, even after 100 years (trees).

If we pick any plant at random, it may or may not be able to withstand freezing temperatures. The determining factor is the plants ability to prevent freezing of bound water. Bound water is the water inside of cells.

There are actually three kinds of water to consider when we discuss "freezing". The water held in soil - When this water freezes, and it can freeze the soil mass solid, it doesn't necessarily kill the plant or tissues. Then there is free or unbound water, also called inter-cellular water. This is water that is found in plant tissues, but is outside of living cells cells. This water can also freeze solid and not kill the plant. The final type of water is bound water or intra-cellular water. If temperatures drop low enough to freeze this water, the cell/tissue/plant dies. This is the freeze damage that kills plants.

Fortunately, nature has an antifreeze. Even though temperatures drop well below freezing, all plants don't die. In hardy plants, physiological changes occur as temperatures drop. The plant moves solutes (sugars, salts, starches) into cells and moves water out of cells to inter-cellular spaces in tissues. These solutes act as antifreeze, allowing water in cells to remain liquid to sometimes extremely low temperatures. The above is a description of super-cooling in plants. Some plants even take advantage of another process to withstand very low temps called intra-cellular dehydration.

The roots of your trees can stay frozen for extended periods or go through multiple freeze/thaw cycles w/o damage, so long as the temperature does not fall below that required to freeze intra-cellular water. If roots remain frozen, but temperatures remain above killing lows, dessication is the primary concern. If the tree is able to take up water, but temperatures are too low for the tree to grow and make food, stored energy becomes the critical issue. Dormant and quiescent trees are still using energy from their reserves (like a drain on a battery). If those reserves are depleted before the tree can produce photosynthesizing mass, the organism dies.

There are a number of factors that have some affect on the cold-hardiness of individual plants, some of which are length of exposure to seasonal cold, water availability (drought stressed plants are more cold tolerant), how recently planted/repotted, etc

No one can give a definitive answer that even comes close to accurately assessing the temperature at which bound water will freeze that covers an entire genus, or even species. Unbound water is of little concern & will usually freeze somewhere around 28*.

Some material will be able to withstand little cold & roots could freeze/die at (actual) root temperatures as warm as 25-27*. Other plants may tolerate much colder actual root temperatures - as low as 10*. There's just no way of knowing unless you have a feeling for how cold-tolerant the genetic material the plant was derived from might be, and finding out is expensive (from the plant's perspective). ;o)

It's wise to remember that root death isn't instantaneous at one particular temperature. Roots succumb to cold over a range of chill with cultural conditions affecting the process. The finest roots will die first, and the slightly thicker and more lignified roots will follow, with the last of the roots to succumb being the more perennial and thickest roots.

Since any root death is a setback from an energy allocation perspective, and root regeneration takes valuable time, it's probably best to keep actual root temperatures in the 25-40* range as long as we can when the tree is resting, even though the organism as a whole might be able to tolerate lower temperatures. Even well established trees become very much like cuttings if all but the roots essential to keep the tree viable are lost to cold. Regeneration of roots is an expensive energy outlay and causes the trees to leaf out later than they normally would and shortens the natural growth period and reduces the potential increase in biomass for the next growth cycle and beyond."

Summary of what I originally put forth: If you repot in fall, you should protect roots against freezing temperatures or you will lose a portion of the roots. It is an expensive outlay from an energy allotment perspective for the tree to have to regrow these lost roots. The energy that goes into regeneration of roots lost to cold could/would have been used by the tree for foliage production and branch extension. Winter-killed roots represent a loss in potential biomass increases and it makes no sense to adhere to a practice that doesn't take cold-damage into consideration - unless you wish to use it as a tool to slow trees down.

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Comments (16)

botann
13 years ago
last modified: 8 years ago
I would pot them up now. I always repot or plant anything I buy from a nursery as soon as possible....even in July.
tapla (mid-Michigan, USDA z5b-6a)
13 years ago
last modified: 8 years ago
Avoid repotting deciduous tees when they are in leaf unless it's an extreme emergency. The best time in your zone is in spring immediately before buds move. Pot-up now, into a similar (to what it's in now) soil and do your repot in spring of 2010. That will also give you time to reconsider using the 1:1:1 Bark: Turface: Grit mix, even though the 5:1:1 mix is still a much better choice than most bagged soils. ;o)

Al
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If you potted-up this spring, you can pull the plant out of the poor soil and stick it back in a better mix. Even though it's never a good idea to have dissimilar soils in the same container, it's better than trying to do a full repot on a deciduous tree in leaf. That exercise usually involves a very hard pruning of the canopy and a loonng recovery period, if it doesn't do the tree in. If you didn't pot-up this spring, let us know & we can explore some other alternatives. Al
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Holly, no problem on the thread hijack... we're all working toward the same goal here :) Now that I've gone back and read every message in Al's "Trees in Containers" threads, I realize I probably should have posted there in the first place. Blake, thanks for all your help. I appreciate the advice, and what you've suggested seems to be consistent with everything else I've read. That being said, I'm in a better position than Holly to experiment, give that I have 6 (soon to be 9) trees to nurture (or torture). Like Holly, I received these recently via mail order. I purchased the young trees recently because I have a 7' Sango Kaku that I believe is infected with Pseudomonas. I decided that, in the event I end up watching my tree suffer a slow death, I'll comfort myself by taking care of some younger Acers that may one day earn the job of replacing my Sango Kaku. Since I've ordered the trees, I have come to realize that there is a lot more to caring for them than I originally anticipated. There is an amazing amount of helpful information in this forum alone. I appreciate all the time everyone here has spent building such a large wealth of information, and hope to someday contribute some useful experiences of my own. As my brain is always in sponge mode, I've been trying to understand more and more about tree growth, container gardening, soils, etc. In the interest of furthering that understanding, I decided to select a candidate (victim) to move into the gritty mix. I'll likely be moving the rest into the 5-1-1 mix or something similar as was suggested. I am, however, a visual learner, so I decided the best way to learn my lesson was to subject one of these poor young trees to what I'll describe as a partial "repot". About 24 hours ago I moved the Trompenburg into a larger pot with gritty mix and a wick. I took it out of its current pot, and carefully removed around 75% of the soil from the root ball by repeatedly dunking it in a bucket of water and poking it away with a small screwdriver. The roots had done a pretty good job of filling up the original container. I didn't prune them, nor did I mess with them much other than to untangle them a bit. My hope was that by minimizing any damage to them, I might make this "repot" a bit more successful. I watered thoroughly then poured on another gallon of water that had some Mycorrhizae and superthrive mixed in. My plan is to root prune and do a full repot next year if the tree survives this ordeal. I plan on observing it and hopefully learning from this experience. I consider it a training exercise to prepare for the disaster scenario where I may some day be forced to repot a tree that is in leaf. Please let me know if you think there is something I should have done differently (given my fabricated disaster scenario). I've included some pictures below of the 6 trees: Trompenburg, Sister Ghost, Seiru, Olsen's Frosted Strawberry, Kogane Sakae, Japanese Sunrise. These were taken just a few minutes ago. Most of the trees are still stretching out after their exciting adventure with the fine men and women of the US postal service. Thanks again for all your help. -Chris
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If one drain hole didn't work for you, 10 more won't make a difference. Good drainage and ample aeration are a couple worth inviting to your party, so you probably need to give some consideration to your choice of soil first, and watering habits second. If you can't water your tree to the point of soil saturation and a good amount of water exiting the drain hole when you water without having to worry about root rot and the back-sliding you described, you're sacrificing a lot of potential and your soil is inappropriate. You'll want a soil that's at least 75-85% larger particles - like pine bark, e.g. It will make a significant difference in your plants' health and in your margin for error ..... it just makes life easier. What I use: The soil in the middle is also excellent: Al
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StaceyBeth, I think re-potting now is fine. I just re-potted about 30 JMs, and they're all doing great, and not a leaf lost. Here's what I do: 1.) Use good potting soil. My custom mix is 2/3 Pro-mix Organic potting soil, and 1/3 Miracle-Gro African Violet potting soil. It has a little fertilizer in it, and a lot of finely ground bark. 2.) I use thick-walled plastic pots. I think this helps with temperature issues in the hot summer. (I'm in TN, and the average temp now is 90 degrees!) 3.) I re-pot, spreading roots out into the new soil a bit; then and give the plants a huge soaking. Leaves, soil, everything. Then I put moss in all the pots. Looks great and helps in other ways. 4.) I put the re-potted trees in my air-conditioned garden house for 3 days and let them rest. 5.) After 3 days I move the trees to my 'holding area' under some big dogwoods, where they get a few hours of early morning sun. Automatic sprinklers water them every other day. After 2-3 weeks in the holding area they are ready to be moved to other locations or planted out. I haven't lost a single tree using this approach, and I re-pot any time during the growing season. Here's a little slide show that might give you an idea. Maple order Regards, K4
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herman_neutics
13 years ago
last modified: 8 years ago
Take,

In zone 7 repotting in Fall is a good idea.

I agree that it's not ideal to repot a fully leafed out plant. If your plants are badly rootbound it's probably worth it to pot them up and do a bit of freeing up of the roots. If they are not so bad I'd wait until fall and repot when the leaves start falling. In my part of Z7 there is 8-10 weeks or so of soil temps where roots will grow after they have been pruned. Also Fall pruning gives a bit more insulation to the roots when If you're anywhere near a Northeast US WholeFoods Market the 'Organic Mechanics' mix they sell is a pretty good media as is and does not use peat at all.

Here is a link that might be useful: repot fall or spring?
takeaphoto
Original Author
13 years ago
last modified: 8 years ago
Everyone, thank you for your suggestions!

Herman, thanks for the link - very interesting. I think I will wait and repot them in the Fall. It looks like some people are having really good results with this method.
tapla (mid-Michigan, USDA z5b-6a)
13 years ago
last modified: 8 years ago
From an energy management perspective:
Whether or not it is advisable to prune roots in fall depends on whether or not the plant will be over-wintered at below freezing temperatures. If the tree is kept under cover and from freezing, it is fine to repot in fall. If it is to be kept in the ground, or will be subject to freezing temperatures, it's best to wait until spring.

Roots are not all equally hardy. Fine rootage is less cold tolerant than partially lignified roots and MUCH less cold tolerant than fully lignified roots. Repotting in spring before budswell guarantees that the fine rootage will not be killed as a result of freezing, whereas trees potted in fall run the risk of having to lay out energy to grow roots, only to have them freeze and die, in which case the tree has to lay out double the energy to regrow the roots in spring.

I'm not sure I understood this: "Also Fall pruning gives a bit more insulation to the roots when Why would fall pruning insulate roots at less than 15*?

Al
herman_neutics
13 years ago
last modified: 8 years ago
Al,

"If it is to be kept in the ground, or will be subject to freezing temperatures, it's best to wait until spring". Did that come out of your text book? LOL you make plenty of pronouncements. Don't you agree its good practice to provide some credible citation when dispensing 'facts'?

re 15F. Above 15F the roots will be ok on their own with or w/o insulation provided the cold period is not extended. Below 15F the roots will benefit from the added insulation.
Those details are based on my experience in Z7 and agree pretty much with what Whitcomb says in his container culture text.

In zone7 Fall there is plenty of time for roots to get a start on re-establishing if the pruning occurs on time. The discussion would have more credibility if replies were tempered with relevant experience.
dawgie
13 years ago
last modified: 8 years ago
I would go ahead and repot your maples now, as long as the new growth has hardened off. If the new growth is still tender, wait until it hardens off. I have successfully repotted containerized Japanese maples throughout the year and have never lost a tree. Although fall, winter and early spring may be ideal, containerized plants are much better able to withstand the shock of transplanting than B&B trees.

A few tips. Try to repot on a cloudy cool day if possible. Avoid disturbing the root ball as much as possible unless the tree is root bound, in which case you should gently separate the roots on the outside. Use good quality potting soil that drains well and a container large enough to give the tree room to grown, but not too much bigger. Water immediately after repotting but do not fertilize. Keep your trees in a shady location for at least a week and water as needed. Mulching around the tree will help it retain moisture better.
herman_neutics
13 years ago
last modified: 8 years ago
"I lecture regularly by invitation" LOL ..the lack of an invitation isn't going to stop you!

My point is that relevant experience is crucial. If you had experience growing Acers in Z7, using a few different approaches, I would feel your points had traction.

We learn best not from dogma but rather from sharing relevant experience and insights.
tapla (mid-Michigan, USDA z5b-6a)
13 years ago
last modified: 8 years ago
I usually find that those resorting to personal attacks have little to contribute that is positive. There is nothing dogmatic about me - I'm always most interested in learning new things and adopting them into my methods. I'm also unsure how you can discount long and substantial experience rearing a wide variety of deciduous and coniferous trees in containers only one zone removed from yours and TaP's, saying it is irrelevant, but ..... whatever.

Interesting that the text you quoted so thoroughly refutes your offerings. I can't understand why someone would intentionally jeopardize the well-being of their trees and advise others to do the same. It's better to be safe than sorry - trees only die once. Experience means nothing if we gain that experience doing something dogmatically, clinging to 'facts' that are erroneous. I think the forum is capable of deciding whose offerings ring true, so we'll leave it at that.

Dawgie - there is a distinct difference between repotting and potting-up. TaP was asking about a procedure during which the plant would be bare-rooted and the soil changed. It would be inappropriate to undertake this type of extensive work while the tree is in leaf. Repotting (again - not to be confused with potting-up) out of season is a good way to lose a tree.

Al
takeaphoto
Original Author
13 years ago
last modified: 8 years ago
I really appreciate everyone's suggestions on this topic. I think you guys (Al and Herman) both have very valid points.

Herman has had good results repotting in the Fall for z7, so although it may be unconventional, it works.

But for someone with not much experience like me, I think I will go with Al's suggestion to be safe and pot-up now. I moved to Memphis recently so I'm not sure how cold it can get here.

I have two Sango Kakus and I may try both method and see how they turn out.

Again, I appreciate that everyone took the time to offer their advice and knowledge. I've been learning a lot from reading this forum.
botann
13 years ago
last modified: 8 years ago
Al, thanks or clearing up the terminology. Re-potting is not a good idea to do now for most people and most plants.
Potting up can be done almost anytime here.
I built an automatic misting system under lath on the northeast side of my house. Part of it has bottom heat for cuttings. I can get away with a lot using it.

Here is a link that might be useful: Pictures of my garden
deep___roots
13 years ago
last modified: 8 years ago
I just repotted a 1 gallon Boskoop Glory into a 2 gallon. The leaves were not looking quite right and upon inspection of the root ball I found lots of places where the soil had washed out leaving small pockets where pillbugs had taken up residence.
So that was a problem. I screened me some oak leaf mold and added a little potting soil and bark to make my new soil mix. The repotting was successful and the plant looks better. Beautiful cultivar is Boskoop Glory.
kaitain4
13 years ago
last modified: 8 years ago
takeaphoto,

I live an hour and a half from you and have several hundred JMs. I repot them whenever I feel like it and never have a problem. I use a good organic mix with Myco fungi and keep them in a cool, shady spot for a week or two after potting up. My grandmother used to say you can re-pot anything at any time if you give it enough water and shade, and I've found this to be true. I've repotted in winter, spring, fall and even in the scorching dog-days of August with excellent results - but my preferred time to re-pot is spring. This gives the tree all season to stretch the roots out into the new soil and have them mature before winter. Then they're all settled in for a long winter's nap! Just don't fertilize JMs when you re-pot. You don't want any new growth in late summer, as it won't harden off properly before freezing weather hits (had to learn this the hard way). Wait a year and then use slow release organic ferts (to prevent nitrogen burn) in early spring.

Regards,

K4
tapla (mid-Michigan, USDA z5b-6a)
13 years ago
last modified: 8 years ago
Perhaps you're treating the roots gingerly and "potting-up" w/o problems while the trees are in leaf, but if you're truly doing a repot, including proper root-pruning, I sincerely doubt there are no difficulties.

Al
kaitain4
13 years ago
last modified: 8 years ago
For the most part I'm potting up, as you describe it, but I've gotten in plenty of stock during the summer that had been bare-rooted for shipment that was in full leaf when I got it. They did just fine being "repotted". Again, good soil, water and shade seems to work for me. In fact I just repotted one today in full leaf that I had to carry on the plane with me 1/2 way across the country. I'm not worried about it surviving.

In my garden, potted maples are a temporary evil as I prepare the raised beds for my collection. I have every intention to put them all in the ground. About 1/2 way there.

K4

K4

Just purchased Japanese maples, when to repot?

tapla (mid-Michigan, USDA z5b-6a)

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