Is it too late to repot my…..?

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This question is regularly asked by beginners in bonsai. The answer given is usually along the lines of ‘repotting deciduous species must be done as the buds swell and before the leaves open.’

For many years I have stuck with this repotting rule but recently have started to question its validity. Sure it works but is it entirely accurate? Some new information has indicated that this rule may be far more prescriptive than necessary. I have seen staff at commercial bonsai production nurseries potting up trees during summer. They have to, to keep up with demand – does this only apply to young ‘mallsai’ or could it mean that other bonsai might survive out of season repotting?

We are now aware that most Australian Native plants actually prefer to be root pruned and repotted during the warmer months. Why are Aussie natives so different from their exotic cousins? They all have leaves, bark, roots, sap, cambium, etc. Recently some experienced growers pointed out that growers in Melbourne have been repotting cedars (Cedrus sp) during summer with great success. One grower advocated repotting on ‘the hottest day of the year’.

All these facts have led me to question the strict rule on late winter repotting so I have started a trial to find out one way or the other.

These 2 trident maples were selected as test subjects. Note that they are relatively young, expendable plants (which may have some bearing on the results). They were both repotted on 16 Nov 2012. Note that the smaller one is growing strongly and has lots of fresh shoots. The larger tree has been a bit drier and has little active growth.

Trident maple in 15 cm pot

 

the smaller one in a 10 cm pot

 

 

 

 

 

 

 
After pruning the roots

 

 

 

 

 

 

 

 

back into the same pot

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After watering in to the pots both trees were returned to the growing benches in full sun (although surrounded by other trees which gives some protection)

 

 

Several weeks later the smaller one has burnt margins on the remaining leaves but both appear otherwise healthy. 

 

 

 

 

 

The leaves on this smaller one had been sheltered from direct sun by the growth above and other plants around it so the leaves were not sun hardy. The leaves on the larger one are still ok.

 

By Dec 4 both trees have produced healty new shoots with no apparent ill effects from out of season repotting.

 

after 18 days both trees have healthy new shoots

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
A further update on this experiment: Both trees have survived and thrived. By January 28 2013 both had strong new growth and are ready for trimming.

Jan 28 - recovered perfectly

11 thoughts on “Is it too late to repot my…..?”

    • Hi Scott,
      At this stage I am only offering the possibility of out of season repotting and continuing my trials. I will continue to repot my good trees when they are dormant until I have more fully explored the possibilities of repotting out of season in my area. Climate may also be a factor. This worked here but may not necessarily apply in other regions. Other growers are welcome to undertake trials and pass on the results.
      I have successfully repotted (young) black pines when they are in active growth and can’t see any reason why Acer palmatum should be any different to tridents. More still to explore. Anyone who has tried out of season repotting is welcome to contact me to pass on any details.
      Neil

  2. Interesting read Neil…..

    I too have re-potted out of season. I found that root pruning of Acer Palmatum is a bit much for summer for them and have lost a few as a result even though they were kept in the shade and given good after care.

    I have just potted up and root pruned a heap of Trident seedlings with good success overall. I have lost approx 5% of these but I think that is acceptable considering I cut off the tap root and all but a few lateral roots. (these were all kept in full sun)

    I also recently (early December) re-potted some Acer Palmatum & Acer Ginalla & Japanese Black Pines which I bare rooted then soaked in rhyzotonic (a hydroponic root tonic) and potted up from normal potting mix to an inorganic mix spreading roots radially. This I found great success with 100% survival however I did lose the apex of one of these maples so I think it should only be done on expendable trees and not your favourite trees. The Japanese black pines which were root pruned have survived so far whereas I have only about 5% success with the JBP seedlings which I cut off all the roots and treated as cuttings (mind you a day of 43 degrees may well be the culprit here)

    I really think boundaries can be pushed, we just have to be willing to experiment and share our experiences. Thanks for sharing Neil, and keep up the great work

    • Thanks for the feedback Luke,
      I agree that this sort of experimental work should be done on expendable trees until we can be sure of the parameters for success. I am quite surprised about your jbp seedling cuttings but this may reflect conditions. I don’t bother with seedling cuttings any more. I get very similar results cutting the JBP seedling roots like you do with trident seedlings – cut tap root right back to the first few lateral roots at potting up. After a few years you cannot tell the difference. I am interested in your experience with Acer palmatum. I intend to try these sometime soon. I wonder whether putting yours in the shade influenced the results?

      Neil

  3. Hi All,
    I have also just potted up around 100 Trident Maple seedlings, having pruned the tap root and some lateral roots, and also piched out the top of the seedlings (to encourage branching) in recent warm weather, with 98% success. The seedlings are being forcefed with Powerfeed, and are putting on good growth. To introduce a variable, I potted up half the seedlings in a premium brand name type potting mix, and the other half in an inorganic diatomite mix. The seedlings in the brand name potting mix seem to have more growth at this stage.
    I would be keen to repeat this experiment again next year; any hints on the best place to purchase some seed?

    • Thanks for that feedback Luke. It will be interesting to see how your potting mix trial goes in the longer term.
      I have trident maples in my garden that produce abundant seed and a range of Acer palmatums that also yield good seed. Email me – neil@shibuibonsai.com.au – around March and we can discuss seed supply.

  4. Hi Neil, Thought I would update you on my experiences since my out of season repotting experiment.
    Majority of my trees repotted in December are going strong. I think I lost a couple of moosewood maple seedlings (Acer pensylvanicum) and I lost 1 of my Acer Palmatums but I think this was from a rogue slug ringbarking the trunk.
    I also repotted and pruned the tap root off of a heap of trident seedlings around late January (Some from seed I got from you, and some from the same seed batch as Luke P.) Ive lost 3 out of approx 70 seedlings but they had weak roots to begin with, and perhaps shouldnt have had the tap root pruned.

    I will coninue to experiment with how far we can push the boundaries, but only on expendable stock. Keep up the great work.

  5. Hi Neil,
    I am in Zambia…Our climate is the same as yours, except that our winter might be milder…up to 10C average lowest temperature.
    I have had a nursery for many years…normal plants, not bonsai.
    Started bonsai last year October…Being eager and never considering before replanting time, I have dug out of my garden many varieties of shrubs and trees, some bought in packets also and bare rooted. I started barerooting in November aand I am still at in till today which is April.
    The weather is still good, and warm, but we are in autumn now…Never lost a plant to date.
    I plant all my cuttings and barerooted trees, in pure river sand, in Shallow containers…no organics till I see them grow. Then I apply on top a layer of caw manure and do that twice a month. I also water them with caw manure liquid solution which I keep in drums.
    Have not lost any tree yet…All the best. Neli.

    • That is great feedback Neli. Great to hear from Africa. Have you bare rooted any deciduous trees over summer or have they been tropical varieties or evergreens? Other growers from more tropical climates are also confirming that repotting while the trees are actively growing works well for them and I believe it will work just as well with deciduous trees.

  6. I have been digging all year round trees from the bush. They are deciduous here. I lost a occasional one from a batch of trees but dont think it has much to do with the time of repot. My friends in SA kept telling me every month. You can not dig trees this month. They will die. But I kept on digging and they kept surviving. I keep them in the shade for a month at list. Still planting them in the usual river sand well sieved. I have not missed a month digging trees. Some come from very arid areas, with almost no roots. Some are just large truncheon cuttings from branches high up on the trees, with diameter up to 30cm. They are also growing…I actually had no fail with them, though I have not done too many of them. Today I posted on the SA forum. I dont think I will ever know which month not to bare root trees, since I have had good results all year round. I shall post what new things I experiment with.

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