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I usually burn dried coconut husk and thorny stems from my lemon plants and I winder if the ash produced from burning such stems and leaves or paper can be a good way to fertilize plants? Or I need to mix it with compost? How or what do I do with that ash?

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  • I've used wood ash on soil just to get rid of it; in small amounts it will do no harm and really not do much good, either. Maybe increase the tilth of the soil over time, but that's never been my intent.
    – Jurp
    Nov 23, 2021 at 0:34

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Wood ash traditionally has a small amount of potassium, like a per-cent. It depends on the wood. So if mixed with compost, it will add a trace of potassium (K). I have read that potassium from wood ash was used to make soap; the difference is that for soap making, the potassium is leached (dissolved) out of a "large" amount of ash and concentrated. Looking on the net, I only find info on "artsy craftzy" fake soap. A little explanation: K - potassium, is the lye of real soap. The burned ash contains K2O ( potassium oxide) , very water soluble. In water it makes KOH, potassium hydroxide,= lye. Sodium can be be used but there is very little in ash.

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I would recommend not to use ash for lemon trees.

Ash may be used as fertilizer (but attention: it may be strong, so not too much, as you should not use too much of chemical [dry] fertilizers), just you may concentrate some heavy metals, so not too much also in long term (few "burned" trees for a garden, per year, may be ok, it is recycling, but more... maybe you should check the origin on ash [check online about component of different ashes]).

That was in general, but lemon trees require slight acid soil. The problem is that ash usually is very alkaline, so it will ruin the acidity of your soil. You may correct it, but why going with such troubles? For this reason usually nobody use ash for lemon trees (and citrus in general, but also for acidophile plants).

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  • I made the ash from lemon tree. I was interested in using it on other non citrus plants.
    – 4-K
    Nov 23, 2021 at 10:25
  • @4-K: pH is not maintained with burning. Ash from lemon trees should still alkaline. By burning, you free CO2 (which it is acid) and so you get alkaline ash. But I'm also not sure that pH is conserved in total (pH is about chemistry), so this explanation may be wrong. In any case I would not consider ash as acid. Nov 23, 2021 at 10:31
  • so adding little bit of ash is not harmful for other plants?
    – 4-K
    Nov 23, 2021 at 10:39
  • @4-K: in general no. It could improve soil (if it was too acid), and it is still a fertilizer. In past it was used as fertilizer. The problem is that now we may burn too much wood, and put it just in our small vegetable garden. And also we tend to burn much more stuffs (ink of newspapers were made with lead, in past). I use it as fertilizer and as snail barrier. Nov 23, 2021 at 11:01
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In terms of commercial fertilizer, average wood ash would be about 0-1-2 or 0-1-3 (N-P-K).

The major elements of wood ash include calcium (up to 30%), potassium (~3–4%), magnesium (~1–2%), manganese (0.3–1.3%), phosphorus (0.3–1.4%), and sodium (0.2–0.5%).

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"Wood ash is a source of potassium(K). But it (K) is easily washed away by water so if it has rained after the fire went out the potassium is gone." - a local gardening book in Bulgarian

"Wood ash is a strong source of carbon for a compost pile. If your compost pile is mostly greens - grass, manure, kitchen scraps - adding a carbon source will improve the smell, rapidity and end result. It will also enable preserving the nitrogen from the decomposing matter." - plenty of sources

Now the embers are another matter. They are extremely strong chemically (nothing eats them) and can remain in the ground for thousands of years. Which is actually good news as research has shown they are an excellent soil amendment.

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