I'm looking for some advice on a few of my Coccothrinax. I have 3 Coccothrinax moaensis, 2 C. orientalis, and a C. spirituana that have developed a bit of yellowing and especially the brown necrosis on the leaf tips. A month ago, they looked good, besides some yellow from deficiency on the older leaves and very minor brown tips. Starting in the beginning of June, the browning got really bad and have spread down the tips of the fronds. Initially, I thought they started to brown because it has been very dry and hot, and I was not watering them enough, around a couple inches of soil had no moisture. Since then, around 2 weeks ago, I have made sure to water them every 2-3 days and maintain a moist root ball. Despite giving them more water, the necrosis has continued to spread down the leaves, and is a bit more noticeable on the newer fronds, which concerns me.

So, what does this look to y'all? The necrosis and some of the yellow seems to be a root issue to me. I am starting to wonder that there has been some root rot, but with how much they have gone in between watering sessions, I am not sure how well an anaerobic environment for root rot pathogens would have survived. Also, the soil they are in is incredibly fast-draining. It is a mixture of garden soil meant for good drainage, coarse sand, and a lot of limestone. Maybe 1 part limestone to 2-3 parts soil? I tend to eyeball it till it is the consistency I like. When watering, the water drains quickly through (within seconds) and does not ever have a chance to pool on the surface. It allows the soil to be moist without being mucky and overly saturated. Until I had a place outdoors, I made this mixture purposely to avoid root-rot when I had to grow these all year indoors under grow lights. It worked great and I had no issues with yellowing or browning. They have been outside for over a year now, and went through the South Florida winter with no rot issues (colder, dried out much slower, and more rain). So that is my confusion on it being root rot. Also, I fertilized with PalmGain about 2 weeks ago when the yellowing and necrosis started to look bad. I don't believe it is fertilizer burn because these issues started prior, and all my other plants did not burn. I also want to add that all my other Coccothrinax species are potted up in this mix and look great. Even some more arid and finicky species like two other C. spirituana, C. ekmanii, C. alexandri, and boschiana look good.

Lastly, my plan to hopefully help them is to exchange some of the old soil with fresh soil without disturbing the root ball too much. I also have a commercial-grade fungicide that was recommended on this forum at some point for root rot. I would like any advice. Also, if anyone has any other advice on anything I can overall improve, I would love to hear.

You can’t say for sure without sticking a finger in there daily, but man, those mixes look dry and sterile. How’s the sun on that balcony? It would be easy to dry and fry in this weather. In summer, I have some potted coccos out back, and water every 2-3 days, filling a tray of standing water under each of them. Most days they sit with some standing water in the trays. Of course, if it’s wet-rot, this will finish them off quick.

1 hour ago, Looking Glass said:

You can’t say for sure without sticking a finger in there daily, but man, those mixes look dry and sterile. How’s the sun on that balcony? It would be easy to dry and fry in this weather. In summer, I have some potted coccos out back, and water every 2-3 days, filling a tray of standing water under each of them. Most days they sit with some standing water in the trays. Of course, if it’s wet-rot, this will finish them off quick.

There is a thin layer of limestone on top to make it more decorative, it does contain more organic soil underneath. But I agree, I think there is too much rock and sand in the overall mix. I am going to carefully look at the roots today to see if there is any obvious rot and will also stick them in a more part-shade location. Balcony can get very hot and dry, and wind probably does not help especially since they are 7 stories up. There is some shade in the late afternoon to evening, but not till 6-7pm this time of year.

I looked in Paul Craft's "Palms of Cuba" book and he has a valuable section on the cultivation of these species. One thing that jumped out to me was that palms native to heavy ultramafic soils don't do well with a lot of calcium. This is what can cause them to stall and slowly decline. This could explain why they looked great for a while, but as the calcium leached from the limestone into the soil over a year or two it may have built up a lot. The soils they come from are also high in magnesium.

My plan now is to transplant them into a soil blend that is pH neutral or more alkaline mix while slightly mimicking the nutritional content in their native soils. That seems to be the best mixture will be a combo of peat, coarse sand, perlite, and bark. I also read somewhere that lava rock is good because it allows for drainage and it is pH neutral. I will try to find a ratio that allows it to drain but also hold onto moisture. Next, I will place in a more shaded location away from direct sun. Looking at habitat pictures, it seems like young seedlings are shaded by lots of larger plants offering protection. Lastly, in case the issue is also stemming from a soil pathogen, I will use the fungicide to treat or prevent the issue if it is there and apply a low dose of PalmGain.

Thank you for the response. How does this plan sound?

Not sure of the specifics on these, but certain parts of Cuba are very floody with lots of rain in the hot-wet season. Your plan sounds as good as any. Sometimes it’s a bit of trial and error.