Curl leaf mahogany leaf tip yellowing

[GreatBasinBonsai]

I apologize in advance because I know there are a zillion reasons for leaf tips, yellowing, but I’ll try to provide as much information as possible, and see if anyone out there can give me some horticultural knowledge, which would be much appreciated.

This is a collected curl leaf Mountain mahogany (cercocarpus ledifolius), and I am growing it in large (1/4 inch+) grain pumice, with very little fertilizer. I am using @Brian Van Fleet ’s fertilizer cakes, applied extremely lightly.

Its water is from a local reservoir, and has a slightly high pH.

It is now about four years post collection and some of the leaf tips are turning yellow. Also, the the leaves that have grown post collection are somewhat small, but that’s no surprise.

I’m really trying to keep it as healthy as possible, with not much available literature of the specific horticultural requirements of this tree. It is a nitrogen fixer, and I observed new nitrogen root nodules when I repotted it this spring. So I think it is doing what it’s supposed to, but there’s clearly something not quite right, and I’m trying to identify what the cause of that could be.

Anyway, thanks to whoever wants to throw me their two cents. Peace!

 

[Wires_Guy_wires]

My thoughts are:
Yellow can mean a couple things: nitrogen, sulfur, calcium.
Nitrogen deficiency would start from the bottom and move upwards.
Sulfur deficiency is extremely rare and I've actually never seen it in real life. Well, maybe four hundred times, when someone used the wrong antibiotics in a single batch of plant medium we used in the lab, but it was all one occurrence.
Calcium deficiency or lockout, usually happens with yellowing and orange blots. It (lockout) happens in high pH environments where the calcium accumulates as a salt, rather than as a soluble ion and where the plant has no available positive ions to exchange for the positive calcium ions (since the OH- will take those up to become neutral, very simply put).
Ca deficiency happens in super low pH soils because it stays too soluble.

Since you're dealing with a high pH water, it is probably locking calcium out.
If you can lower the water pH, the issue should stop expanding in a week or so.The foliage that isn't affected should also turn to a darker shade of green since magnesium, iron and calcium are more readily available in lower pH soils. If it wasn't that, then we would have to investigate further.

 

[GreatBasinBonsai]

My thoughts are:
Yellow can mean a couple things: nitrogen, sulfur, calcium.
Nitrogen deficiency would start from the bottom and move upwards.
Sulfur deficiency is extremely rare and I've actually never seen it in real life. Well, maybe four hundred times, when someone used the wrong antibiotics in a single batch of plant medium we used in the lab, but it was all one occurrence.
Calcium deficiency or lockout, usually happens with yellowing and orange blots. It (lockout) happens in high pH environments where the calcium accumulates as a salt, rather than as a soluble ion and where the plant has no available positive ions to exchange for the positive calcium ions (since the OH- will take those up to become neutral, very simply put).
Ca deficiency happens in super low pH soils because it stays too soluble.

Since you're dealing with a high pH water, it is probably locking calcium out.
If you can lower the water pH, the issue should stop expanding in a week or so.The foliage that isn't affected should also turn to a darker shade of green since magnesium, iron and calcium are more readily available in lower pH soils. If it wasn't that, then we would have to investigate further.

Hey, thank you so much, this is very helpful stuff, definitely a good starting point and something I'm gonna look into, I'm going to get a proper pH test kit and start trying to dial in/adjust these parameters. Appreciate you taking time to give such a thorough answer.

 

[Wires_Guy_wires]

Litmuss paper is the cheapest and remarkably accurate. It should cost you about a dollar fifty. And since it's paper, you can just tear of tiny bits.
I think a 100 strip test can last me about 400 measurements.

Citric acid is a great pH downer that is plant safe, but since it is a weak acid, do measure again an hour later; it tends to donate and receive hydrogen, which causes great stability once there's an equilibrium, but huge sways in the mean time.
Once you get down the amount of citric acid you need for a given amount of water, you can probably eyeball it without measuring. But do measure it at least a couple times before you go for the eyeball method. Thankfully that buffering capacity citric acid has, means that even if you overshoot it a little, it'll probably meet somewhere in the middle after some stirring.
I use citric acid to descale my coffee machine too, so buying a kilogram isn't overdoing it.
Do keep in mind that citric acid is not an 1+1 atom acid like hydrochloric acid (H-Cl) but it contains a carbon skeleton that microbes and algae can use. It wouldn't surprise me if a cannister is back to its original pH in a day or two. So make it fresh and mix well.

Anyhow, once the soil pH is within an acceptable range, which can take a lot of waterings, it will then act as a buffering agent itself. Meaning you can do on and off with your special water, and the regular water you've been using. That will over time slowly raise the pH, but plants and soil microbes combat this to a certain extent. My potting soils start out with a pH of around 5 each spring, and by the end of summer they end up being around 7. I start out low so that I can only give tap water until the rain starts falling again in fall.
Rain water should have a lower pH by itself, and you can collect it and use it if you like. It would have a similar effect as the citric acid, but it might take a bit longer and deplete very fast.

 

[GreatBasinBonsai]

Hey I really appreciate that. I got some test strips, and the water I have been using is not as high pH as I had assumed, according to the test strips it's about 6.7. Nonetheless, I have a 300 gallon tote that collects rainwater, and is full, so I have been using that plus a very minuscule amount of vinegar, like half a teaspoon per 5 gallon bucket, plus a very minuscule amount of king Neptune fish emulsion fertilizer, maybe a quarter teaspoon per 5 gallon bucket.

What I'm beginning to wonder, is if I may have been causing some kind of fertilizer burn in the spring which led to the leaf tips yellowing? I was fertilizing a bit more heavily in the spring, alternating a very dilute miracle grow and very dilute king Neptune. I've been looking online and apparently fertilizer burn and certain nutrient deficiencies can have a very similar look, at least from the somewhat unreliable information I can find on the Internet. Sheesh...

I guess just being devils advocate, do you think it could've been fertilizer burn of some kind? The reason I wonder is because these trees grow in such nutrient starved conditions naturally in the wild, which is why they've evolved to become nitrogen fixers I suppose… Anyway curious what your thoughts are on that?

Thanks again, I sure would love to bring some of these lesser-known great basin species into wider cultivation and appreciation as Bonsai. And unless I devoted my entire life to studying them, it's hard to do that alone! So thank you.

 

[GreatBasinBonsai]

One more detail, which I should've mentioned at the first- I did repot the tree this spring, and of necessity I had to cut the roots back somewhat, to remove field soil which I believe was clogging things up and beginning to cause some branch die back. So perhaps the root work alone was enough to stress the tree, and cause yellowing leaf tips once the heat of summer began to set in…? Just throwing that out as another possibility. Thanks again.

 

[Wires_Guy_wires]

Fertilizer burn and an affected root system could sure be at the cause of this all. The symptoms match. But those effects are quite rapid and they should stop expanding after about a month past the injury.

 

[GreatBasinBonsai]

Awesome thank you. For now, I'm going to chalk this up to root damage, and potentially over fertilizing this spring because the yellow seems to be contained, not spreading. I'm writing this reply in case any future practitioners are reading this thread… Thank you again so much, I'll keep you updated if anything changes.

Also, I've been watering with the lower pH rainwater exclusively for the last three weeks or so, and maybe it's just my imagination, and maybe it's unrelated, but it seems to be looking a little happier overall.

 

[treeline]

Always thrilled to see people using Cercocarpus for bonsai! I have three in my garden -- all collected and at different stages of development. Based on my experience, I'd agree that root damage from repotting seems like the most likely cause.

They do seem to be sensitive to root work, especially if the timing isn't perfect. You might consider hosing field soil off in the future if you need to remove more. I've had success using water to clear out west desert clay both post-collection and during repotting. Good luck!