Fertilizer regimen for nitrogen fixing trees? (Curl leaf mahogany)

[GreatBasinBonsai]

I have been obsessed with collecting Curlleaf mountain mahogany (cercocarpus ledifolius) for about 15 years, and I am starting to have some success but there is a missing piece of the puzzle I would love to dial in. They are nitrogen fixing trees and I have heard/read that they require less/little/no nitrogen, but I'm not sure if I'm giving them a proper fertilizing regimen.

They are in pumice, sometimes with a mixture of decomposing pine bark and/or lava and/or spagnum.

I have been using @Brian Van Fleet 's diy fertilizer cakes (thanks and shout out to him ) along with a supplemental variety of kelp, humic/fulvic acids, and root Mycorrhizal drenches. And sparingly on the fertilizer. So basically I AM supplying some nitrogen, in an organic form, with the idea that if they don't actually need it, it will hopefully at least not come in a form that hurts them.

It is also my understanding that perhaps it is nitrifying organisms that are doing the actual nitrogen fixing and not the root tissue itself. So maybe if the bacteria etc aren't using the nitrogen that I am dumping on them, it will just wash away with whatever other nutrients are not needed.

Does this sound like a solid plan? What would you suggest?

I would love to hear from someone who has real scientific information/knowledge/experience, not just conjecture. I have read what little available literature and published papers on the subject I can find, but can't get a real solid answer.

I should mention that the trees I have had the longest are about five years post collection, and although they suffered some branch die back early on (see photo taken this spring during a repot and light field soil removal) they seem to slowly be regaining vigor but i just want to make sure I'm giving them the very best shot at long-term survival, and eventually making the transition into an actual Bonsai Pot, which will probably be at least a 10 year process.

Thanks thanks!

 

[Shibui]

I'm more familiar with the rhizobium reliant nitrogen fixes rather than species that utilize Frankia but they should work in a similar manner. Our Casuarinas also use Frankia to get N and they do just fine when fertilised well.
First lesson is that getting nitrogen from the air is very energy intensive so the bugs expect to get paid well for the work of converting it.
Also, there's no such thing as a free feed.
Trees that fix nitrogen only do it because there's not enough in the environment. They have to 'pay' the resident nitrogen fixers (rhizobium, Frankia) to do the work.
All nitrogen fixers also have 'normal' roots that can absorb N from the soil when it is present.

The upshot of all that is N fixers can grow in areas of low N with the help of their bacteria but can do perfectly well without the bugs when there's good N levels. Feeding your trees won't hurt. They'll probably grow much better when they don't have to pay the extortion demanded by the bacteria to do the work of extracting atmospheric N for them.

 

[Bonsai Nut]

My experience with mountain mahogany and manzanita is less about fertilization and more about soil pH. They are usually found in soil that is low in organic matter and high in pH, and typically don't get a ton of acidic rainfall. Be careful if you plant them in a soil with high organic content, and never use an acid fertilizer. Make sure you don't overwater or let them sit with wet roots. Think of them like desert scrub and try to provide the same conditions.

 

[Deep Sea Diver]

Thinking the very same thing.

It’s more about the pH than providing nitrogen, thus keeping the rhizosphere intact.

Most nitrogen fixing trees are reliant upon the microbes to provide nutrients and it is a big energy pay off to do so. So providing nitrogen will be effective…. however and it is a big however ….trees and shrubs that normally rely on microbes in the rhizosphere given high levels of fertilizer than normally used to tend to abandon the natural nutrient pathways (WSU).

Karen O’Hanlon founder of https://www.probiocarbon.ie/ in a discussion with Ryan Neal on asymmetry mentioned trees relevant upon NPK fertilization also tend to need more insect control and eventually become less resilient.

That said, only know one other member personally how has tried to work with Mountain Mahogany, @August44 If I recall correctly he mentioned the Boise club was working with these plants.

Cheers
DSD sends

 

[Colorado]

I had this mountain mahogany for about 5 years before selling it recently.



I just treated it like all my other trees. Akadama, pumice, lava soil and fertilized with Biogold and liquid fish/seaweed.

I didn’t even know they were nitrogen fixing until just now

 

[GreatBasinBonsai]

Hey thanks so much guys. Yes the pH angle is definitely something I need to consider and I'm going very light on the fertilizer. Thanks @Shibui for the extended explanation on the kind of extortion relationship. I hadn't thought of it in that way but it makes sense. It's encouraging to know that there are others out there who have had these long-term!