Leaf scorch on Japanese Maple (mild weather)

[zeejet]

I have a young Japanese maple (acer palmatum atropurpureum) that had put out a healthy initial flush of growth in early spring, but has started to wilt and develop leaf scorch over the last month.

A few important details about the tree and it’s care to date:

• Received during winter dormancy in early Feb (shipped from Missouri)
• Buds broke in late Feb and spring growth continued through April with hardening in early May
• Fertilizing using Osmocote Plus (15-9-12) in small fertilize baskets since mid-March.
• Leaf scorch began in early May where temperatures are 65-70F during the day and about 50-55 in the evenings. UV Index would be about 9 during sunny days. 50-70% RH.
• The tree was watered with poor quality water (350 ppm TDS with high sodium, calcium and bicarbonate) from Feb through early May.
  • RO water was installed mid-May and the tree’s soil was soaked and flushed with RO. Have been watering with RO since.
• Using a silicon-based foliar spray for sun protection (Superthrive Protekt)

The leaf scorch has been getting progressively worse despite switching to better water and we actually had a mostly cloudy month with not much direct sun. I’m not sure what else there is to do other than shade cloth - but it’s barely June and not hot at all.

Here is what it looked like after initial flush of growth (different lighting):


Here it is now with leaf scorch:

 

[Wires_Guy_wires]

Using a silicon-based foliar spray for sun protection (Superthrive Protekt)

Seeing how this is a low pH material, it might be as protective as it is destructive.
I know some silicates over here are packaged as an anti-mildew product, and it's sodium silicate. The sodium gives the foliage a nice orange burned color. Usually in a spotted fashion.

Keep in mind please, that most studies on silica based stuff rely on the basis of "None versus an X-amount" and that leads to the conclusion that silicates are beneficial.. IF THEY WERE OTHERWISE NOT NATURALLY PRESENT.
In most soils containing perlite, lava rocks, sand or almost everything else, microbes, sunlight and pH changes release silicates pretty steadily. A friend of mine gave me a call a while back about the latest cannabis craze: silicates! Laughing he told me that it was the first time someone was actually selling sand in a desert. Because, really, that's what it is.

Back to the subject on hand, because sodium poisoning isn't completely ruled in..
Is the leaf scorch affecting new growth? Or just expanding on the older foliage?

 

[zeejet]

Back to the subject on hand, because sodium poisoning isn't completely ruled in..
Is the leaf scorch affecting new growth? Or just expanding on the older foliage?

Thanks for the reply!

The scorch is affecting both although more so the older foliage. New growth is largely fine except a few random leaves that have stunted growth and dark "rotted" tips.

Looking at the Protekt product info, it's silicon is in the form of potassium silicate and even considers the product a 0-0-3 NPK fertilizer so sodium isn't what's being added here.

I was really hoping the improvement in water quality (RO with pH of ~6.0 and micronutrients from Osmocote Plus) would halt the scorch, but if it does, it hasn't kicked in yet.

 

[CarpenterDiaz7]

Following for answers as well.

 

[dbonsaiw]

Shooting from the hip, but my guess would be that you cut dormancy short when shipping from Missouri. Tree is trying to bounce back with the new growth. Maybe get it into a little shadier spot and let it recover from being abruptly woken up.

 

[Wires_Guy_wires]

Thanks for the reply!

The scorch is affecting both although more so the older foliage. New growth is largely fine except a few random leaves that have stunted growth and dark "rotted" tips.

Looking at the Protekt product info, it's silicon is in the form of potassium silicate and even considers the product a 0-0-3 NPK fertilizer so sodium isn't what's being added here.

I was really hoping the improvement in water quality (RO with pH of ~6.0 and micronutrients from Osmocote Plus) would halt the scorch, but if it does, it hasn't kicked in yet.

That's good news!
Not sure what I can say about the new growth but the fact that it's less affected can hint towards an issue in the past that has now been resolved.

You say the scorch isn't halted. Does that mean the tips that are scorched, continue to brown further? Or do you mean that they stay as they are?
Just making sure we're all on the same page, as some people sometimes believe that plants can heal dead foliage tips, which plants can't unfortunately.
At some point in time, if the causing agent is gone, it should stop expanding.

 

[zeejet]

Shooting from the hip, but my guess would be that you cut dormancy short when shipping from Missouri. Tree is trying to bounce back with the new growth. Maybe get it into a little shadier spot and let it recover from being abruptly woken up.

Possible, but that was all the back in late February. The first flush was really healthy and has only recently (last month) started scorching.

If dormancy is truly a concern, then I'm properly f*cked because it rarely gets below 45F during the winters here. I guess I'll just need to ride this season out and adjust next year with earlier shading (or give up on JM's entirely for my zone if they fail to go dormant).

That's good news!
Not sure what I can say about the new growth but the fact that it's less affected can hint towards an issue in the past that has now been resolved.

You say the scorch isn't halted. Does that mean the tips that are scorched, continue to brown further? Or do you mean that they stay as they are?
Just making sure we're all on the same page, as some people sometimes believe that plants can heal dead foliage tips, which plants can't unfortunately.
At some point in time, if the causing agent is gone, it should stop expanding.

There was never scorch during the first flush - only in the last month did it develop on older spring growth. Note that spring temps starts in late Feb here in SoCal and new growth often begins in early March for most deciduous species. By May, first flush spring growth has slowed and hardened off already.

The scorch is continuing to spread on the same leaves - I am aware that yellowed/browned parts of leaves are indeed "dead" and cannot be recovered.

 

[dbonsaiw]

Possible, but that was all the back in late February. The first flush was really healthy and has only recently (last month) started scorching.

If dormancy is truly a concern, then I'm properly f*cked because it rarely gets below 45F during the winters here. I guess I'll just need to ride this season out and adjust next year with earlier shading (or give up on JM's entirely for my zone if they fail to go dormant).

I find it hard to diagnose problems even on trees that are right in front of me. That said, a JM will break dormancy, ready or not, if exposed to the right conditions. I find that the buds are able to open and even sustain themselves from nutrients stored in the tree - i.e. the fact that the leaves are open and look healthy is not necessarily an indication that the tree is healthy and will grow well. Case in point, I had many JM cuttings this season that opened and held onto leaves for a month or so - no roots grew and the leaves were being sustained by nutrients in the cuttings. Leaves browned and then cuttings died. I can't say 100% what is wrong with yours, but if dormancy was cut short, the buds could have opened and sustained by stored nutrients. As the leaves grew, stored nutrients ran out and the tree became more dependent upon proper functioning/overall health, it could have hit a bump and leaves started to scorch and fail. I find extension of old growth and new growth a much better indication of tree health. In any event, nothing to do now other than nurse it back to health.

As for dormancy, I'll defer to folks in San Diego. If I could, I'd share some of my NY winter as I despise it.

 

[zeejet]

I find it hard to diagnose problems even on trees that are right in front of me. That said, a JM will break dormancy, ready or not, if exposed to the right conditions. I find that the buds are able to open and even sustain themselves from nutrients stored in the tree - i.e. the fact that the leaves are open and look healthy is not necessarily an indication that the tree is healthy and will grow well. Case in point, I had many JM cuttings this season that opened and held onto leaves for a month or so - no roots grew and the leaves were being sustained by nutrients in the cuttings. Leaves browned and then cuttings died. I can't say 100% what is wrong with yours, but if dormancy was cut short, the buds could have opened and sustained by stored nutrients. As the leaves grew, stored nutrients ran out and the tree became more dependent upon proper functioning/overall health, it could have hit a bump and leaves started to scorch and fail. I find extension of old growth and new growth a much better indication of tree health. In any event, nothing to do now other than nurse it back to health.

As for dormancy, I'll defer to folks in San Diego. If I could, I'd share some of my NY winter as I despise it.

Thanks for the insight - hard to say indeed. Again, I guess I'll have to observe.

For what it's worth, the local wisdom here in San Diego is that JM's will survive with the right care (shade cloth in summer, good quality water, and conservative fertilization) but rarely "thrive" and only look great in early spring (consistent with my experience thus far). It's also said that water quality is a big contributing factor here in SoCal as the tap is very hard, which I only recently "fixed" with RO so it's a bit early to definitively say if it's truly the cause. I guess I just wanted to make sure I wasn't missing something critical in my care that caused the scorch prematurely.

Also, I grew up ion Bronx, NY and remember the winters there. Glad to be out in sunny San Diego, but it's now a tad too sunny in summer and a tad too warm in winter for good deciduous bonsai.

 

[Deep Sea Diver]

If that’s the wisdom, go with it.

Hmm…. Red maples are prone to sun damage, loving more shade.

How much sun (hrs and time of day) is this tree getting in San Diego?

As starters would say place in spot of up to mid morning 10:30 sun and open shade from there.

70% shade cloth would be a good option.

Cheers
DSD sends

 

[zeejet]

If that’s the wisdom, go with it.

Hmm…. Red maples are prone to sun damage, loving more shade.

How much sun (hrs and time of day) is this tree getting in San Diego?

As starters would say place in spot of up to mid morning 10:30 sun and open shade from there.

70% shade cloth would be a good option.

Cheers
DSD sends

I have a cover balcony that faces 210 degrees (South West) so I get zero morning sun and all afternoon sun unfortunately. I have started keeping my JM's under 40% shade all day at this point. The balcony would otherwise receive direct sunlight from about 11AM through sunset (around 7:45PM in end-of-May).

 

[Bonsai Nut]

In SoCal you will struggle with JM due to one of several conditions - (1) high water pH, (2) sun intensity, or (3) low air humidity. If you have a JM that isn't protected when Santa Anas are blowing, the leaves will completely crisp in a single day. In Orange County I could only keep them if they were under 40% shade cloth, with no afternoon sun, and I would bring the trees indoors if the Santa Anas were blowing.

 

[hardtimes]

It’s been so mild here that a couple of my jms are just starting to leaf out. I do have one with slightly crispy leaves that I over watered. Kinda looks like yours

 

[zeejet]

In SoCal you will struggle with JM due to one of several conditions - (1) high water pH, (2) sun intensity, or (3) low air humidity. If you have a JM that isn't protected when Santa Anas are blowing, the leaves will completely crisp in a single day. In Orange County I could only keep them if they were under 40% shade cloth, with no afternoon sun, and I would bring the trees indoors if the Santa Anas were blowing.

Is there any way to receive alerts about Santa Ana wind events? I'm not sure if any have come through but my JM continues to burn and has lost more than half of it's foliage to scorch despite using RO and using shade cloth.

 

[RoadManDenDron]

I only tend to use organic now, but since no one has mentioned it,

How much osmocote is in each of the baskets? How many baskets?

Personally I would not call 19N 'Conservative fertilisation' and I believe the slow release can go overdrive in hot weather

Too many salts around the root zone can draw moisture out of plants

 

[Bonsai Nut]

Is there any way to receive alerts about Santa Ana wind events? I'm not sure if any have come through but my JM continues to burn and has lost more than half of it's foliage to scorch despite using RO and using shade cloth.

It is extremely hard to keep them in SoCal. I tried numerous different cultivars, and they all responded similarly. They would bud out in the spring, and look great for a couple of months until summer temps started to arrive. Then the leaves would start to crisp at the margins. If the winds blew off the desert, all the leaves could completely dry out in a single day - despite being watered. The trees would drop their dried leaves, and then push another round of weaker growth (as if they had been artificially defoliated). This 2nd round of growth might last a week or two, but when dry conditions happened again, the leaves would crisp, and the trees would die.

The only tree that I was able to keep for more than a year was an Acer P. "Sangu kaku" that I kept in the lee of my house, in a sheltered corner, and got no direct sun. Even so, the tree never showed the amazing colors that JM are known for. In the Fall the leaves would simply dry up and fall off the tree - they never showed any fall color.

 

[zeejet]

I only tend to use organic now, but since no one has mentioned it,

How much osmocote is in each of the baskets? How many baskets?

Personally I would not call 19N 'Conservative fertilisation' and I believe the slow release can go overdrive in hot weather

Too many salts around the root zone can draw moisture out of plants

I'm using the 15-9-12 Osmocote Plus in a single small fertilizer basket. I always thought I may be under-fertilizing but I suppose I could experiment with less or use organic to see if that helps. Most modern takes on fertilizing young trees seem to abandon the pro-organic movement and accept chemical fert as acceptable (I've been reading Bonsai Heresy and Modern Bonsai Practice books).

It is extremely hard to keep them in SoCal. I tried numerous different cultivars, and they all responded similarly. They would bud out in the spring, and look great for a couple of months until summer temps started to arrive. Then the leaves would start to crisp at the margins. If the winds blew off the desert, all the leaves could completely dry out in a single day - despite being watered. The trees would drop their dried leaves, and then push another round of weaker growth (as if they had been artificially defoliated). This 2nd round of growth might last a week or two, but when dry conditions happened again, the leaves would crisp, and the trees would die.

The only tree that I was able to keep for more than a year was an Acer P. "Sangu kaku" that I kept in the lee of my house, in a sheltered corner, and got no direct sun. Even so, the tree never showed the amazing colors that JM are known for. In the Fall the leaves would simply dry up and fall off the tree - they never showed any fall color.

I'll likely give JM's another season before giving up in earnest haha. I have a Mikawa seedling that has yet to burn (although leaves are getting a bit big under shade cloth) and I'm cautiously optimistic for that one. The red that's already half-cooked might have to go to another home

 

[Wulfskaar]

I also live in SoCal.

I'm on my third year with a shishigashira maple. The leaf edges on that have crisped every late summer, which gives me very little fall coloring. That's sad because the centers of the leaves have amazing yellow and orange color. But... it still pushes out a whole new set of leaves every spring.

I keep it under a large tree, so it gets dappled sunlight only.

I have also grown a few J. Maples from seed that are doing just fine right now, although it's the same story for them too.

My only advice is to keep Japanese Maples out of the scorching summer sun. If possible, only morning sun. Otherwise, only dappled sun. I also wet the leaves when it's hot/dry when I water, but I'm not sure how much that helps.

I do have a Snakebark Maple that is doing great, but it has very large leaves and long internodes.

I have considered putting my maples in a small greenhouse tent during dry wind events.

 

[zeejet]

I also live in SoCal.

I'm on my third year with a shishigashira maple. The leaf edges on that have crisped every late summer, which gives me very little fall coloring. That's sad because the centers of the leaves have amazing yellow and orange color. But... it still pushes out a whole new set of leaves every spring.

I keep it under a large tree, so it gets dappled sunlight only.

I have also grown a few J. Maples from seed that are doing just fine right now, although it's the same story for them too.

My only advice is to keep Japanese Maples out of the scorching summer sun. If possible, only morning sun. Otherwise, only dappled sun. I also wet the leaves when it's hot/dry when I water, but I'm not sure how much that helps.

I do have a Snakebark Maple that is doing great, but it has very large leaves and long internodes.

I have considered putting my maples in a small greenhouse tent during dry wind events.

Thanks for sharing your experience in SoCal - I think I'll just have to suboptimal conditions if I want to keep these. I'm hoping my mikawa seedling and a grafted summer gold JM will at least survive the summers. The red maple is a random red seedling and likely has no inherent tolerance for sun - it may need to be sold next year if I experience the same issues. I have a SW facing balcony that only gets afternoon sun so it's shade cloth for me it seems.

I've also considered acer oliveranium 'hot blonde', which is purportedly similar in heat tolerance to tridents, but I've also hear that it's got long internodes and large leaves. The only other maple I'd like to try is the acer truncatum, which apparently grows in Taiwan (mostly Zone 11-12). There's a patented cultivar called 'Baby Dragon' that is a dwarfed version and should do well as bonsai. Unfortunately its rare and currently only sold by nurseries licensed by MetroMaple (owners of the patent).

 

[Wulfskaar]

J. Maples are tough to keep here, but I've seen it done.