Root pruning a potted Japanese Maple

Discussion in 'Maples' started by benzmum, Feb 9, 2024.

  1. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    I've had a Japanese Maple in a container for about 20 years. I believe it's an Acer palmatum dissectum, and the foliage is red. It's done really well up until last year, when it developed a lot of lichen growth and didn't produce its usual profusion of foliage (I'll post an image from its glory days). I'm pretty sure it's pot-bound and needs root pruning. I've never root-pruned a container plant before, and I need to know when I can safely do it. Do I have to wait until there's no longer expected frost?
    [I'm not sure my image is going to show, but I'll post this now and go from there!]

    - Linda
     

    Attached Files:

  2. Backcountry Dan

    Backcountry Dan Member Maple Society

    Messages:
    43
    Likes Received:
    54
    Location:
    Wyoming 4b
    Here's a great video from one of the members here. I think it should answer your questions.
     
    Otto Bjornson, AlainK and Acerholic like this.
  3. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    Thanks, Dan. That was very helpful. I think I'll try my hand at the pruning in a week or so, while the tree's still "dormant," as he said in the video. And it was helpful to hear that he saves the fertilizing till spring's actually here.
     
  4. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    Considering the weather this year in Vancouver is on and off regarding winter & spring, can a tree in a container still be considered “dormant?!”
     
  5. 0soyoung

    0soyoung Rising Contributor

    Messages:
    290
    Likes Received:
    377
    Location:
    Anacortes, WA
    Yes, up to the point that leaves are just emerging from tip buds.

    Generally speaking 'dormancy' = no extending growth is happening, not just wintertime. Most Japanese maples produce three spurts of new extension/leaf growth each season with pauses or 'dormant' states between. Indeed one can root prune at those times as well, but care must be taken to prevent desiccation because maple leaves loose significant amounts of water through the leaf surfaces (because they lack a waxy coating).

    Extension occurs because water is loaded into the vacuoles of new cells, The coils of cellulose in the cell walls prevents lateral expansion so that the cell just lengthens. Obviously this process requires lots of water, so root pruning is not advisable at these times (when the tree is not dormant).
     
    Last edited: Feb 28, 2024
    irshmerc, Otto Bjornson, maf and 2 others like this.
  6. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    Hhm…. Not clear on this post, Osoyoung - forgive my ignorance. On Wed. I saw prunus blossoms on 7th west of Clark drive! There’s a low pocket north of VCC where it may be warmer than higher up on Clark. But I wonder if there are signs on my poor Maple that I can look for to tell me that it’s coming out of dormancy, and therefore I’ve missed the root-pruning window? What signs would I look for, and will the poor plants who think it’s now Springsuffer for blooming early
     
  7. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    Oops! Think I posted before I intended to. Apologies, but did you get the gist?
     
  8. 0soyoung

    0soyoung Rising Contributor

    Messages:
    290
    Likes Received:
    377
    Location:
    Anacortes, WA
    The only thing that matters is the state of the tree you intend to repot/root prune. If the buds have cracked on your maple AND leaves are emerging from them, it is too late.
     
    irshmerc, Otto Bjornson and emery like this.
  9. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    Ok, understood - thanks
     
    0soyoung likes this.
  10. Otto Bjornson

    Otto Bjornson Contributor

    Messages:
    303
    Likes Received:
    666
    Location:
    chilliwack BC, Canada (8B)
    @benzmum
    We are located just 100 km east of you in Chilliwack. If you are going to root prune your container grown weeping maple you will still be fine for another week or so. After that I would be hesitant.
    We are planning to root prune a couple of larger container grown trees next weekend as the weather is now seasonally cooler then normal.

    Also, looking at the photo you supplied, it looks like a cedar / wood box?
    My guess after 20 years? it will likely completely fall apart so best to have a new container on hand before you start.
     
    Last edited: Mar 2, 2024
  11. AlainK

    AlainK Renowned Contributor Forums Moderator Maple Society 10 Years

    Messages:
    3,704
    Likes Received:
    5,427
    Location:
    nr Orléans, France (E.U.)
    20 years ?...
    To me it's OK, I don't think my counter will go that far. ;°)

    Best contribution in this thread so far - in my opinion :



    To me, repotting means trimming, pruninge the roots to 1/3rd, or even 2/3rds on young trees in late automn, late winter.

    I also repot trees in a small pot (bonsai, or not-a-bonsai) between mid-June and late July, reducing less of the rootball, at most 1/3rd, prefferably when the weather is not too hot and very rainy, like in Japan.

    It happens (happened) sometimes here.

    Not sure at all it will happen again due to climate change... :-(
     
    maf and Otto Bjornson like this.
  12. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    Good call re the container, Otto! I do have another one that’s currently empty so we’re ready to go. Thanks for the encouragement. I have two young men coming to help me with the project in an hour.
     
    Otto Bjornson likes this.
  13. AlainK

    AlainK Renowned Contributor Forums Moderator Maple Society 10 Years

    Messages:
    3,704
    Likes Received:
    5,427
    Location:
    nr Orléans, France (E.U.)
    I repotted my 'Beni hagoromo' this afternoon.

    I cut 5 cm at the bottom. Before putting it in a new pot, I also made 4 vertical cuts about 2 cm deep around the rootball.
    And I used clay pebbles instead of the 2-3 cm of pozzolane at the bottom of the pot : not as heavy !

    The mix is about the same as usual:
    Compost from a garden centre, composted pine bark and pozzolane (3-5 mm) (about 2-2-1)

    acerp-benihag01_240304a.jpg
     
    Otto Bjornson likes this.
  14. emery

    emery Renowned Contributor Maple Society 10 Years

    Messages:
    3,513
    Likes Received:
    3,714
    Location:
    Normandie, France
    You have employed the professional's approach to root pruning when potting up or planting: remove the braid at the bottom, use a cutter to make 4 slices. I do it with really root bound pots when I've got a lot of the same thing to pot upwards. Most of the time I do the whole teasing thing, but I can't honestly say the maples prefer it.

    I planted 3 birches today, (ermanii, costata, alleghaniensis) which I grew from tiny seedlings to 5l pots. I mention it only because, I don't generally use clay pebbles (too large I think), but the B. costata I apparently had some lying around and had put into the mix. This one had the best top, and is leafing out, which prompted me to get them into the ground. But the root was the smallest of the 3. Whether this is down to the species or the mix, I have no idea.

    Birches hate having their roots disturbed, so it's a bad idea to let them get root bound, and even better to plant quite small. Root pruning a birch the way we do maples would possibly set it back a year or two! I had to tease a few out to avoid encirclement on the ermanii anyway.
     
    AlainK likes this.
  15. AlainK

    AlainK Renowned Contributor Forums Moderator Maple Society 10 Years

    Messages:
    3,704
    Likes Received:
    5,427
    Location:
    nr Orléans, France (E.U.)
    I went on with this 'Atropurpureum'. It was one of 5 seedlings that were in a 12 cm wide pot.
    I took this one to try to make it a bonsai, on the photo you can still spot the spiraling scar that the wire made.

    But the others died, and I thought there are more suitable cultivars for bonsai, so I put it in a rather shallow big pot. It stayed there for years. LMast year, I noticed it couldn't stand the heat and drought, and it was high time to repot it, which I did today :

    acerpatro01_240304a.jpg acerpatro01_240304b.jpg acerpatro01_240304c.jpg acerpatro01_240304d.jpg

    Oh my, yes it was high time ! And look at all those weeds, tsk...

    I have "varnished" pots that I wanted not to use for maples : when in the sun, they are like an oven, and keep the heat during the night. And it gets harder and harder each year to move them !
    But I think the colour matches that of the leaves, it's got a lot of new substrate, and I can find a place where it only gets the morning sun for a few hours, so I think it will be OK.
     
    dicky5ash and Otto Bjornson like this.
  16. dicky5ash

    dicky5ash Generous Contributor

    Messages:
    1,411
    Likes Received:
    2,589
    Location:
    Northampton Uk
    IMG_5649.jpeg IMG_5648.jpeg IMG_5650.jpeg Smallest one first, I could have gone at it harder but it will do for this year
     
  17. dicky5ash

    dicky5ash Generous Contributor

    Messages:
    1,411
    Likes Received:
    2,589
    Location:
    Northampton Uk
    Repotted a 7 foot Ukigumo today, I was so surprised at the poor quality of the root ball..I’ve had it 8 years or so and it’s a healthy tree, not by the look of the roots though! I think I’d used a bad batch of compost originally..I remember getting a few bags of this very black looking compost, mixed it up as usual with the other ingredients but the 2 or 3 trees I used it on have not grown good roots.

    I’ve repotted with a new mix and plenty of mycorrhizal fungus additive.
    IMG_5663.jpeg IMG_5666.jpeg
     
  18. dicky5ash

    dicky5ash Generous Contributor

    Messages:
    1,411
    Likes Received:
    2,589
    Location:
    Northampton Uk
    IMG_5656.jpeg IMG_5654.jpeg IMG_5660.jpeg IMG_5658.jpeg IMG_5659.jpeg IMG_5662.jpeg

    Ive done 4 lots of root pruning in large pots today, am ruined!!!
     
    Otto Bjornson, maf and emery like this.
  19. AlainK

    AlainK Renowned Contributor Forums Moderator Maple Society 10 Years

    Messages:
    3,704
    Likes Received:
    5,427
    Location:
    nr Orléans, France (E.U.)
    Well done mate !

    I also repotted a few this afternoon, but in pots not as big as yours, the largest about 2/3rds of the last you posted.

    I know the feeling, my back aches...
    But we had sunny patches this afternoon, it was about 20°C, that's what we call "une fatigue saine" (healthy fatigue - or would you say tiredness ?...)
     
    dicky5ash likes this.
  20. dicky5ash

    dicky5ash Generous Contributor

    Messages:
    1,411
    Likes Received:
    2,589
    Location:
    Northampton Uk
    Thanks for the encouragement Alain. You did well too..it does does make you feel good when you get a few done. Normally I’d say “healthy fatigue” but it didn’t feel so healthy pulling that Reticulatum out of the pot and manhandling it for pruning lol

    It was the same here sunny spells but a little cooler, about 15c.

    I have just 2 large ones left to do - the Peaches and cream, that been in the same 85ltr plastic pot for probably 10years…really needs a refresh. The Osakazuki is in a 130ltr clay pot, I did that one about 5 years ago..I remember it was really hard getting it out because the inside of the pot is rough texture - I need a sword to loosen it around the edge lol
     
    emery and AlainK like this.
  21. benzmum

    benzmum Active Member 10 Years

    Messages:
    57
    Likes Received:
    8
    Location:
    Vancouver
    It is truly exhausting work! I had two young men alternately saw the roots of my red maple while the other held it steady on its side. It took a full hour. I watched and supervised, wringing my hands. I was worn out just watching how hard they worked! Now I hope to see a very happy maple in a month.
     
    emery, Otto Bjornson and AlainK like this.
  22. Otto Bjornson

    Otto Bjornson Contributor

    Messages:
    303
    Likes Received:
    666
    Location:
    chilliwack BC, Canada (8B)
    @dicky5ash
    Nice work! no need for a gym membership!
     
    AlainK likes this.
  23. Otto Bjornson

    Otto Bjornson Contributor

    Messages:
    303
    Likes Received:
    666
    Location:
    chilliwack BC, Canada (8B)
    Got the last re pot done today. Our pixie has been sitting in a temporary pot for a couple of years now. Decided to drop it into a hybrid cement pot. This pot we picked up a few years back, a combo of cement and fiberglass. About half the weight of cement but supposed to be even stronger. We have never found them again as we would have bought a couple more. Came with 3 nice pre drilled holes in the base, so great for drainage.
    IMG_5398.jpeg
     
    opusoculi likes this.
  24. mobiledynamics

    mobiledynamics Member

    Messages:
    49
    Likes Received:
    9
    Location:
    Zone 7A - Long Island
    This may be a subjective question. Root pruning due to exhausted pot media or that due to pot bound.
    If pot bound, whether you root prune and upsize pot or root prune and put back in same pot.....do you guys go the *extra* mile* of inoculating the roots with Myco. Inoculating the roots does tell it to make more roots...so if one has pruned due to pot bound, do you let the roots -naturally and slowly- do their thing or give it a boost by inoculating them. I'm tend to errr on the latter and anytime some is removed from a pot and put back, regardless of prune or not, I will inoculate it
     
  25. AlainK

    AlainK Renowned Contributor Forums Moderator Maple Society 10 Years

    Messages:
    3,704
    Likes Received:
    5,427
    Location:
    nr Orléans, France (E.U.)
    Personally, I don't.
    Maybe it could help, but if the tree is in the right soil, I don't think it's necessary.

    Maybe I'm wrong, but I tried it with bonsai and seedlings (maples and pines) and didn't see any difference...
     
    Margot and Otto Bjornson like this.

Share This Page