Chinese Elm temperature

[WeeTree58]

Hi there all
I live in Melbourne Australia and have not long started the last month of spring so although we're having some very warm days temperatures are still changeable.
I have a problem with out of the ordinary leaf drop and having eliminated most things like over/under watering, enough sunlight (the tree lives outside), fertilizer etc I was wondering if it maybe heat stress.
It gets pretty hot on the balcony where it is but I thought I controlled temperature pretty well.
Anyway can anyone out there give me their opinion on maximum temperature limits that they stick by. I have read varying articles, one that says up to 32c and another that says 25c so big difference.
I have read also that optimal temperature for bonsai is 20-30c but of course that may vary between tree species.
If anyone has any info or has experienced and fixed a similar problem I'd love to hear from you
Cheers
Glenn

 

[Shibui]

Hi Glenn. Some pictures might give additional clues to what could be happening. Often experienced growers can pick up something you have not even thought about just from the pictures of the tree and surrounds. Take a couple up close, some from mid range and another to show surrounds.

I don't think temperature is the problem. My Chinese elms don't seem to have any issues up to 42C up here. I provide some light shade through the hottest months but that would not reduce temp by very much from ambient given that temps are measured in shade anyway.
I suspect you still have some problem with roots - probably related to watering. Watering bonsai in small containers is not as easy to master as many beginners believe.

 

[WeeTree58]

Thankyou very much for your reply Shibui I will take some photos tomorrow and post them.
I've had issues with Trident Maples in the past as well but not this spring as the Maple is bolting away.
I took both the Maple and Elm out of their bonsai pots and put them back into large nursery pots to thicken the trunks etc and increase general health of the tree. It has worked a treat for the Maple and I thought initially for the Elm but it's gone backwards just a bit, still healthy but something isn't right as it seems stressed to be shedding green leaves in spring.
I appreciate any help you can provide after viewing the photos.
Cheers
Glenn

 

[TimIAm]

In Sydney and no problem with having elms in full sun here. Same as Shibui, I don't move my elms unless temps go above 40.

How long between the repot and the leaf drop? Is it possible you did the repot and then put the tree out in full sun immediately? Did you do any root work, or bare root etc. when you did the repot? Did you change the soil type when you switched between the bonsai pot and into the nursery pot?

Is it shedding this seasons leaves? In Sydney, my elms don't drop leaves during winter, they typically do it when the new leaves push through at the beginning of spring.

 

[WeeTree58]

Thanks for replying TimlAm
The only thing that's changed from normal is the soil, since the slip pot it's gone from bonsai soil to a good quality organic potting mix with blood and bone and perlite.
No root prune, was inside for 2 weeks after the slip pot, it's dropping a combination of leaves including the first flush leaves and it's really hard but being careful re over/under watering so I don't know but really frustrating.
I had a similar issue with a Trident Maple and did the same system and boy it's taken off.
Do you think it's not getting enough sun, it gets sun pretty much from early morning till 1.30-2.00
so it certainly gets sun.
Hopefully with help I can find the problem.
Cheers
Glenn

 

[TimIAm]

It was inside for 2 weeks, has it been outside since the repot? When it's getting sun, that is direct sun and not balcony / indoors through a window etc.?

Many years ago I left about 10 trees with a neighbour while I went overseas for 4 weeks. They over watered every day and had my trees in almost no direct sun. Some of the trees dropped all their leaves (but eventually recovered) and others absolutely thrived putting out a mass of new growth. Different species can react completely different in the same conditions.

That being said, elms can usually take a beating. Most often, even if they drop their leaves they bounce back. I'd be more concerned if you started seeing die-back on branches.

 

[WeeTree58]

It was inside for 2 weeks, has it been outside since the repot? When it's getting sun, that is direct sun and not balcony / indoors through a window etc.?

Many years ago I left about 10 trees with a neighbour while I went overseas for 4 weeks. They over watered every day and had my trees in almost no direct sun. Some of the trees dropped all their leaves (but eventually recovered) and others absolutely thrived putting out a mass of new growth. Different species can react completely different in the same conditions.

That being said, elms can usually take a beating. Most often, even if they drop their leaves they bounce back. I'd be more concerned if you started seeing die-back on branches.

Inside for 2 weeks and then back outside on the bench in the open / sun.
I do things properly and very thoroughly, don't want to get things wrong and try my utmost to maintain healthy trees so this is bugging me

 

[WeeTree58]

Here are some photos of my bonsai area and the Elm.
This is the 2nd flush of new growth this growing season after pruning back from 8-10 internodes in most areas of lignified branching.

 

[Shibui]

The pot is big so I guess it should not be drying out too much. There is the possibility that it stays wet down deep in that pot but you sound pretty confident that watering is adequate.
The only other possibility I can suggest is too dark way back there in shade.

Did this one lose leaves over winter? Chinese elms sometimes don't go fully deciduous. That can affect leaves in spring.

 

[WeeTree58]

Yes I doubt it's drying out and I check it regularly with a moisture meter trying to keep it in the moist range.
I only pull the cover up if it's going to get above my perceived temperature maximum and usually at night to prevent prying eyes doing something as a wee while ago had some stolen.
Yes it lost most it's leaves over winter but the weather here in Melbourne is variable at the moment but I wouldn't have thought cold enough to plunge the tree back towards dormancy.
So I don't know it's a weird one especially how the tree sprouted it's first flush at start of spring.

 

[TimIAm]

Just asking again; since you did the repot, it was inside 2 weeks, but how long since then before it started dropping leaves?

The new growth looks healthy. My only guess is that the partial shade its getting has caused it to drop leaves that it doesn't think is necessary maybe with the combination of staying inside for a couple of weeks.

The leaves that are being dropped appear (maybe I'm seeing it incorrectly) to be internal and not the new growth tips. The tree may be seeing the internal growth as surplus to its needs if not getting enough direct sunlight.

Was it in the same position last growing season (spring/summer)?

 

[WeeTree58]

Yes it was inside for no more than 2 weeks as normal repotting after care then it has flushed with new growth really well and at a guess I suppose I noticed the first signs of leaf drop about 3 weeks ago so it was slip potted on July 25 so about 2 months without any issues.
Although maybe hard to see the new buds now are affected some not growing and some dying off also some internal growth is affected especially that right side branch as you look at the photo.
Do you think I'm too cautious with all my trees as far as temperature/sun exposure goes with not only the Elm but all my trees, looking after them too well.
The only thing is because of work I can only water in the morning before work and late afternoon when I get home.
It's the same with the sun shade on hot days, if I don't put the shade up before I go to work it doesn't get up.
What do you think?

 

[WeeTree58]

Yes it was inside for no more than 2 weeks as normal repotting after care then it has flushed with new growth really well and at a guess I suppose I noticed the first signs of leaf drop about 3 weeks ago so it was slip potted on July 25 so about 2 months without any issues.
Although maybe hard to see the new buds now are affected some not growing and some dying off also some internal growth is affected especially that right side branch as you look at the photo.
Do you think I'm too cautious with all my trees as far as temperature/sun exposure goes with not only the Elm but all my trees, looking after them too well.
The only thing is because of work I can only water in the morning before work and late afternoon when I get home.
It's the same with the sun shade on hot days, if I don't put the shade up before I go to work it doesn't get up.
What do you think?

Sorry that should be 3months after the repot

 

[WeeTree58]

Sorry again, yes the tree is in the same place on the bench but I could move it to sunnier position

 

[WeeTree58]

I have just had a thought that when the first flush had extended to 7-8 internodes and hardened off I pruned back to 2-3 and depending on the individuals thinking that may be good or bad.
Some schools of thought say prune and others say no pruning in spring.
No pruning because the tree is regaining it's energy from pushing the first spring flush and if you spring prune you're depleting the tree of it's energy by making it produce a 2nd flush.
Just a thought

 

[TimIAm]

It's hard to be accurate over the internet with something that is a bit tricky, so these are more just thoughts.

- If you are getting dieback at the tips or smaller/ newer branches are starting to die off, you have something serious you need to adjust, like something went wrong with the repot or something wrong with over or under watering or it is not getting anywhere near enough sunlight. But this doesn't appear to be the case, based on the photos.
- If you are getting dieback on internal leaves, it's possible insufficient light or a small possibility it's a watering issue. Another small possibility, it was weak and the repot has caused it to drop some leaves. Personally, if I have a tree I'm concerned about during repot, I put it in partial sun for no more than a week. I've never heard of keeping a tree indoors for 2 weeks following a repot; that being said, there's a lot of things I haven't heard and admit I don't know everything. If it is internal dieback, it's likely it will bounce back - if you're happy it's getting enough sun and not over/under watering; elms are pretty hardy.
- I used to get some dieback with elms years ago when I didn't know better and would prune too late in Autumn, causing the tree to put out new growth heading into winter.
- Cutting back new growth can have it's benefits if you're not doing it across the whole tree. The problem with a healthy elm is less likely to be a tree regaining it's energy, it's more so a wasted opportunity for growth. Elms will push out long, ugly (in terms of design) flushes of growth, but allowing them to extend and stay around is what will help your tree grow thicker. Selective pruning in spring is fine, if it's with purpose. Sometimes it's better to have a scruffy looking tree through spring to help drive growth and future work.

Do you think I'm too cautious with all my trees as far as temperature/sun exposure goes with not only the Elm but all my trees, looking after them too well.

It really depends on the species. Most of my trees are in full sun unless I know it's going to be above 40 or a sudden heat surge in spring. However, there are a few of my trees that do worse in full sun. I personally avoid cold climate species that can't handle a full day of Sydney sun. Part of that is experience with your trees. With insufficient sunlight you will see some trees extending towards the light and may get internal leaf drop where light isn't reaching. Otherwise, if you are happy with how your trees are progressing, then don't worry about it.

With watering, sometimes with premium potting mix, it can hold a lot of water. When you come back home is the top couple of centimetres dry? Just thinking about how your soil is draining, especially if the pots are in partial sun and they are larger pots. I have a few ficus which I keep as larger trees to take cuttings from and they sit in potting mix and only get watered every second or third day.

Apparently moisture meters are not a good indicator for use in pots.

 

[Shibui]

After repot my trees go straight back to their spot on the bench. Deciduous trees have no leaves when repotted so no point keeping them shaded. Most repotting is early spring when temps are mild and sun is not strong so even evergreens go straight back to the benches after repotting here. Natives are usually repotted in November here. By that time the sun is starting to get a bit hot but I still put the trees right back where they belong and that's mostly with no extra shade.
One of the problems with moving trees into shade is that the leaves adjust to cope with shady conditions. Then the tree is suddenly moved back into sun which can sometimes burn those leaves and the tree needs to readjust leaves to cope with sun again.
I think it is definitely possible you are being too cautious with these trees which may NOT be looking after them too well. I suspect some of the care you are giving these trees may actually be detrimental.