Help... Black on soil

Help needed folks.
I have a black shiny growth on a number of trees this last few weeks both deciduous and conifer.
I’m thinking it has something to do with a mild wet summer here in the North of the UK.

Since midsummer’s day I have applied
1 dose of organic fert
1 dose of cold press seaweed
1 dose of chemical fert
1 dose of cold press seaweed
1 high dose of chemical fert.

The trees most badly affected are the ones due to be repotted in spring

The growth is hard almost plastic feel and has joined the top dressing particles together. It smells of green chlorophyll.

All advise welcome.

I, too, have had this happen on my trees also. I experience this when I place my homemade Fert cakes on the soil surface; after a few days, I begin to see this blackish formation. In the two-three years I’ve been doing this, I’ve never really seen/experienced any adverse responses from trees, and surmised that it was probably a reaction between the moss in my top dressing, and the fertilizer itself. It doesn’t happen until I apply fertilizer, and NEVER forms on soil that doesn’t have moss growing on it. I’m curious to see what other responses we might receive concerning this.

Looks like you have algae growing on the soil surface. Your pots are likely staying too wet.

Did you use any type of seaweed or fish emulsion when this happened?
I’ve used both the organic and chemical before and never experienced this… Although I’ve never give such a heavy feeding in a short space of time before.
Can you remember what weather was at the time… We had a brilliant spring but a wet and mild summer.

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Definitely has an algae smell to it chuck.
All my trees top dressing has been greenish this year with the seaweed emulsion.

Yes, fish emulsion…specifically Alaska Fish Fert (hydrolysate) - not straight, but as a Fert cake ingredient.

I’m in USDA 7b, (Tennessee), so it stays pretty humid here, as well as hot. Our spring was extremely wet this year, but it’s not seasonally specific (that I have noticed). Just know that I’ve seen it before and decided to chime in.

It is not connected to the Fish emulsion but is linked to the weather. I live in NW England as well and I am guessing our weather has been very similar and I have the same problem with a few of my trees. The constant damp wet and humid conditions and the lack of any real summer weather since the spring heatwave hase been the cause. I only use solid organic fertiliser. It is algae and in your photo you can see areas without the black slime the substrate is green with algae as well.

We need better weather to let it dry out.

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It’s a slime mold, quite common, fairly harmless in of itself.

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Thanks everybody.
Hopefully we will get another week or 2 of good sun before autumn pulls in.

Hi Michael. I have it on a lot of my trees, but only the ones with compost in the mix. It usually starts when i know it’s going to be hot I use a hose instead of a watering can (way too many trees for my own good!). As compost holds onto water longer than akadama it ensures they stay moister for longer (without being waterlogged all day). Plus as you know we’ve had an awful wet summer. Obviously the downside is the slime. I wait until it hardens up then simply move it around to break it up. If it gets too bad I’ll even scrape off the top layer and replace it.

@CarlisleMikeUK , any long-term effects from this?
Good, bad, etc?

Hi Kurt this was 2020.
No ill affects from this.
The little juniper didn’t grow much in the over sized pot and or soil mix, so was repotted in a smaller deeper pot in pure Akadama spring 2021.
Im using the same fert as last year and up to date have not seen this again.
I can only put it down to too much soil for the amount of roots and the soil not as free draining.
If it happens again in autumn I’ll keep you posted mate

Should I remove, or alter top dressing at all.? I live in Louisiana and it gets humid here and warm. Sometimes we have wet spells her as well.

I leave it, maybe break up with a chopstick so air and water gets under. I am asuming this is the microbiom bloom growing and digesting the organic material on the pot surface. Unsightly, yes, however doesnt seem to hurt the tree. And, its doing exactly what you want… releasing the nutrients.
With good topdressing and moss, you wouldnt see the growth. With teabags, it would be in and under them.
Unfortunately, the mass dries out and gets hard. I crumble it up and spread out. I have trouble growing moss here too (inland pacific NW, desret).
Bonsai On!

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I tend to see it when I have a real wet period of time. Do you notice this as well?

So, you are see it worse this summer? How well is your top dressing growing moss?
Yes, it is growing / spreading when it is wetter. I notice it more after it gets dried… Eating the organic material on the surface.
Does NOT appear to hurt trees. Just ugly.
Several of my trees have it way more than what you showed. I spread a dried powder organic fertilizer on most of my trees in mid spring. It has mostly gone away now. Dried up from the heat. 102 most of the last week…
Are you seeing any of the motile (moving) gelatenous slime mold? Google it. Its entertaining…