Chinese elm leaves going yellow

[Alex_B]

Hi all,

I've had my pre-bonsai Chinese elm for about a month now and on hot days I've been watering it everyday to make sure the soil is always moist. I've noticed the soil on top is very compact so I can't really put my finger in to see if it is moist further down so I've always just made sure the top of the soil is always moist so I'm not super sure whether I've been over watering it.

I've noticed some of the leaves have been turning yellow, I'm not sure whether this is simply because they are old or maybe I've been over watering it. It might also be getting to much sun, I tend to leave it in full sun for the whole day if it isn't to hot and if it over 30 degrees I put it in shade for the afternoon sun so I think it should be fine sun wise.

If any one has any ideas why the leaves might be going yellow I would love to know as I'm not sure if I'm doing something wrong.

[TimS]

Mine is doing the same, they are deciduous after all, and in stress they can drop all their leaves. I don’t think it’s anything to worry about personally

[Keep Calm and Ramify]

Mine is doing the same, they are deciduous after all, and in stress they can drop all their leaves. I don’t think it’s anything to worry about personally

Likewise, a seasonal change is in the air! What a re-leaf!

Alex, here is a close up shot of some of mine at the moment. Many shades

cm.jpg

[shibui]

Yellow leaves can mean a number of things.
- As already pointed out it can be natural end of season change but I think it is way too early for that yet.
- It can point to sick roots - possible over watering.
- Conversely, it can point to under watering. That looks like quite a large tree in a very small pot. Are you sure that watering once a day is enough in summer? If the soil is as compact as stated maybe once a day will be enough but mine need watering twice a day right through summer.
- Yellow leaves is also a sign of nutrient deficiency - esp low N when older leaves turn yellow but newer leaves are still green.

From this far away I can't pinpoint the actual cause. You are in a much better position to try to narrow down the cause.
If you have not been feeding regularly try stepping up the liquid feed for a start. If that's the problem the leaves should green up in a couple of weeks.

Check the rootball after watering and again before watering. Slip it out of that pot and check the roots. It will slide right out without damaging roots so you won't hurt the tree but should be able to get a far better idea of how effective your watering is. You hould be able to get a better idea of whether you are over watering (roots still soaking wet when watering is due) or under watering (roots are dry) I've found that root bound trees are really hard to water properly because there's no spaces left for air and water to get into the root ball proper. Normal watering just runs around the sides and out the drain holes. Soaking is the only answer until you can repot.

[Alex_B]

Thanks for the help TimS and Keep Calm, I thought maybe it was due to the wild weather we have been having in Melbourne but wasn't to sure.

Yellow leaves can mean a number of things.
- As already pointed out it can be natural end of season change but I think it is way too early for that yet.
- It can point to sick roots - possible over watering.
- Conversely, it can point to under watering. That looks like quite a large tree in a very small pot. Are you sure that watering once a day is enough in summer? If the soil is as compact as stated maybe once a day will be enough but mine need watering twice a day right through summer.
- Yellow leaves is also a sign of nutrient deficiency - esp low N when older leaves turn yellow but newer leaves are still green.

From this far away I can't pinpoint the actual cause. You are in a much better position to try to narrow down the cause.
If you have not been feeding regularly try stepping up the liquid feed for a start. If that's the problem the leaves should green up in a couple of weeks.

Check the rootball after watering and again before watering. Slip it out of that pot and check the roots. It will slide right out without damaging roots so you won't hurt the tree but should be able to get a far better idea of how effective your watering is. You hould be able to get a better idea of whether you are over watering (roots still soaking wet when watering is due) or under watering (roots are dry) I've found that root bound trees are really hard to water properly because there's no spaces left for air and water to get into the root ball proper. Normal watering just runs around the sides and out the drain holes. Soaking is the only answer until you can repot.

I have been feeding it every week and a half with powerfeed and have been doing that since I got it with the longest wait time between feeds being a week, I thought every week/fortnight would be enough but maybe not?

I didn't think about taking it out and inspecting the roots but I guess it is easily done since the soil is pretty tightly bound. I will definitely start doing that as a check and inspecting it more thoroughly.

I thought it was a pretty small pot for a big tree and was planning on slip potting (not sure if that's the right term but essentially I mean just transferring it into a bigger pot without trimming any roots) into a bigger pot near the beginning of spring but perhaps I should do that now? I'm just not sure if it is a good time to even just transfer it into a bigger pot but if that will help it then I am more than happy to do it.

[Phil Rabl]

Slip-potting looks like the way to go. You can do that at any time. In 2016, Shibui (who knows plenty) posted advice on slip-potting eucalypts. That advice stands for exotics too. Here is the link: https://www.ausbonsai.com.au/forum/view ... 78&t=22565 (in case the link doesn't work, the topic was Eucalyptus tereticornis Bonsai Trail).

[Alex_B]

So I had a good look at the roots today and it seems like over watering is definitely the culprit here. When I took the tree out of the pot it was still dripping wet from its last watering, I think the issue is the soil is so compact that it isn't draining all the water out properly so I am going to slip pot it and see whether I can save this tree. It doesn't seem like its too far gone but I could very well be wrong there. I am leaving it out of the pot for now just to let the roots dry a bit and get some air flowing into them but I am not sure what a good soil mixture is Chinese elm.

I have heard people say not to buy pre-made bonsai soil mixtures but to simply mix your own. I have heard pine bark and rough sand is good for well draining bonsai soil but I am not sure.

[shibui]

Chinese elm are pretty tolerant. They have to be since they are a favorite tree for beginners so manage to tolerate all sorts of abuse. I think it will recover just fine.
I don't believe there is any such thing as a preferred soil mix for Chinese elm. If you ask 10 different bonsai growers you will get 10 or maybe more? different answers and most of them will tell you that theirs is definitely the only one you should use
The truth is that growers can tailor their watering and care to suit the soil mix so all sorts of mixes are possible provided you care accordingly. Personally I use just one mix for all my trees. That way I know how much to water to keep it damp. I also know how many years until the mix starts to break down, etc. A single mix for all works for me.
Pre-made bonsai mix is OK provided you match watering and care to suit the mix. Some high end regular commercial potting mixes are also suitable but look for the ones with relatively large particles rather than mostly sawdust.
Mixing special mixes for each tree means you need a range of components on hand, somewhere to store components and premixed batches, etc. I don't believe it is worth the hassle for maybe a very minor advantage. there are also issues with proper additives - Iron, pH adjustment, nutrients, etc which are all vital to successful potting mix.
My preferred mix is 70% 6-10mm pine bark and 30% propagating sand with some other minor additives to balance the mix.

Feeding fortnightly should be more than adequate so cross nutrient deficiency off the list which brings the possibilities back to water.

Slip potting now is probably a good idea. Don't go too big for a start. Unused mix can go stale and adversely affect the plant so just up a size or 2 each time. Keep a good eye on trees after slip potting. Often there is lack of good contact between the old root ball and the newer mix so water and roots will not cross the barrier easily. this can mean the inner root ball can stay dry while the new outer mix has good moisture levels or it can mean that the roots suck the old inner bit dry but moisture can't cross from the damp new mix across to the older area with roots.
Usually roots will quickly grow into the new mix and everything is OK but occasionally there seems to some difference and we see problems so you should just be aware of possibility.
I would do a full bare root and root prune next spring. Nebari is important for bonsai and it does pay to get it right from the start. When roots are older and thicker it becomes more difficult to make changes and when the tree is larger hard pruning to sort out root problems can be more difficult for the tree.
Best to do roots early and spring would be a good time.

[Alex_B]

Chinese elm are pretty tolerant. They have to be since they are a favorite tree for beginners so manage to tolerate all sorts of abuse. I think it will recover just fine.
I don't believe there is any such thing as a preferred soil mix for Chinese elm. If you ask 10 different bonsai growers you will get 10 or maybe more? different answers and most of them will tell you that theirs is definitely the only one you should use
The truth is that growers can tailor their watering and care to suit the soil mix so all sorts of mixes are possible provided you care accordingly. Personally I use just one mix for all my trees. That way I know how much to water to keep it damp. I also know how many years until the mix starts to break down, etc. A single mix for all works for me.
Pre-made bonsai mix is OK provided you match watering and care to suit the mix. Some high end regular commercial potting mixes are also suitable but look for the ones with relatively large particles rather than mostly sawdust.
Mixing special mixes for each tree means you need a range of components on hand, somewhere to store components and premixed batches, etc. I don't believe it is worth the hassle for maybe a very minor advantage. there are also issues with proper additives - Iron, pH adjustment, nutrients, etc which are all vital to successful potting mix.
My preferred mix is 70% 6-10mm pine bark and 30% propagating sand with some other minor additives to balance the mix.

Feeding fortnightly should be more than adequate so cross nutrient deficiency off the list which brings the possibilities back to water.

Slip potting now is probably a good idea. Don't go too big for a start. Unused mix can go stale and adversely affect the plant so just up a size or 2 each time. Keep a good eye on trees after slip potting. Often there is lack of good contact between the old root ball and the newer mix so water and roots will not cross the barrier easily. this can mean the inner root ball can stay dry while the new outer mix has good moisture levels or it can mean that the roots suck the old inner bit dry but moisture can't cross from the damp new mix across to the older area with roots.
Usually roots will quickly grow into the new mix and everything is OK but occasionally there seems to some difference and we see problems so you should just be aware of possibility.
I would do a full bare root and root prune next spring. Nebari is important for bonsai and it does pay to get it right from the start. When roots are older and thicker it becomes more difficult to make changes and when the tree is larger hard pruning to sort out root problems can be more difficult for the tree.
Best to do roots early and spring would be a good time.

Once again shibui thank you so much for all the advice you have given me you have really taught me a lot already.

I just bought some new orchid pots this morning so I am waiting for them to get delivered and then I will slip pot the tree.

I would definitely prefer a good all round mixture instead of specializing it for each tree as I am going to slip pot my juniper in spring so I would like to use the same mixture. By minor additives do you mean like some small rocks or do you mean added nutrients in the soil?

I will definitely do a good root prune in spring and hopefully it will be just the refresher the tree needs plus I have spotted a new nice thicker roots already in the pot so I am looking forward to getting a closer look at them.

[TimS]

I slip potted one of my larger chinese elms a few weeks back because it was needing 3 waters a day in the heat and i couldn't keep up with that with work commitments. It's already putting on new shoots everywhere with the new, much wider pot, so they bounce back quickly.

You shouldn't have any issues at all banging it into an orchid pot now, especially if it's a bit too wet. Don't get too hung up on soil mixtures, i'm with Shibui in that i use one commonly available nursery mix for all my trees and just tailor my watering to how each tree reacts. I know that it tends to break down after 3 years so i aim to repot every couple of years which is never an issue for what i grow. If i was growing pines and i wanted to leave it longer between repotting i might mix up something different, but generally speaking it doesn't faze me too much.

[shibui]

By additives I mean other nutrients that are not available in modern soilless mixes or things that get tied up by the decaying pine bark. Iron is a big one. Many people who make up a mix don't understand and the plants end up anemic from lack of iron or dwarfed from lack of N, etc.
The mix I use has: slow release iron, controlled release fertiliser, micronutrients, iron sulphate, dolomite, gypsum and zeolite. All those in the quantities needed for healthy growth and to balance the pH and what the pine bark will rob from the mix as it begins to decay.
that's just nutrients. Potting mix also needs to have physical properties - water holding capacity, air filled porosity and just enough weight to hold the plant down in wind but not too heavy for the grower to pick it up occasionally.

Potting mixes are quite complex and a lot can go wrong when you don't understand. Much easier to let someone who knows do the calculations and formulations and just buy a bag or 2 if that's all you need.

[Alex_B]

You shouldn't have any issues at all banging it into an orchid pot now, especially if it's a bit too wet. Don't get too hung up on soil mixtures, i'm with Shibui in that i use one commonly available nursery mix for all my trees and just tailor my watering to how each tree reacts. I know that it tends to break down after 3 years so i aim to repot every couple of years which is never an issue for what i grow. If i was growing pines and i wanted to leave it longer between repotting i might mix up something different, but generally speaking it doesn't faze me too much.

Potting mixes are quite complex and a lot can go wrong when you don't understand. Much easier to let someone who knows do the calculations and formulations and just buy a bag or 2 if that's all you need.

Thanks for the advice Tim and shibui I think buying a nursery mix is probably the best way to go for the time being and when I get a bit more experience and feel like trying to mix my own then I will have a crack.

Again thanks for all the advice, I've already learn't so much from this forum haha.