# [Wet Thumb Forum]-Wood Ash as substrate fertilizer



## HanshaSuro (Jun 22, 2004)

A question for the fertilizer pros out there:

In my never-ending quest to put together a reasonably priced and nutrient rich substrate, I thought of wood ash as a possible substitute for layerite or similar substrate fertilizers.

The idea was born from listening to my girlfriend talk about her upcoming wood-kiln firing. (She is a ceramicist.) They are going to have piles of wood-ash left over after the firing is complete and it is likely going to just be disposed of in one way or another.

The idea would be to take a bunch of it and pack it into the bottom of the aquarium while dry and then cover it with Schultz Aquatic Plant Soil (keeping with the low budget theme).

Since she has access to this kind of information, I asked my girlfriend to do a little research about the chemical composition of your average ash and this is what she found for Pine:

10.1% Potassium Oxide
10.6% Sodium Oxide
46.1% Calcium Oxide
13.5% Magnesium Oxide
4.8% Iron Oxide
8.4% Silica
and lots of stored CO2

Not terribly high in iron, unfortunately. Would definitely wish that it was switched with the calcium. Come to think of it, is all that calcium going to put the pH through the roof?

Anyway, I've put it out there. What do people think?


----------



## HanshaSuro (Jun 22, 2004)

A question for the fertilizer pros out there:

In my never-ending quest to put together a reasonably priced and nutrient rich substrate, I thought of wood ash as a possible substitute for layerite or similar substrate fertilizers.

The idea was born from listening to my girlfriend talk about her upcoming wood-kiln firing. (She is a ceramicist.) They are going to have piles of wood-ash left over after the firing is complete and it is likely going to just be disposed of in one way or another.

The idea would be to take a bunch of it and pack it into the bottom of the aquarium while dry and then cover it with Schultz Aquatic Plant Soil (keeping with the low budget theme).

Since she has access to this kind of information, I asked my girlfriend to do a little research about the chemical composition of your average ash and this is what she found for Pine:

10.1% Potassium Oxide
10.6% Sodium Oxide
46.1% Calcium Oxide
13.5% Magnesium Oxide
4.8% Iron Oxide
8.4% Silica
and lots of stored CO2

Not terribly high in iron, unfortunately. Would definitely wish that it was switched with the calcium. Come to think of it, is all that calcium going to put the pH through the roof?

Anyway, I've put it out there. What do people think?


----------



## Roger Miller (Jun 19, 2004)

Wood ash is loaded with minerals. Back before the days of large-scale mining when wood was a common fuel wood ash was the primary source of some minerals.

One of the problems with wood ash is that it is extremely alkaline. People used to extract lye from ashes. Another problem is that is contains carbonates -- enough that it can fizz pretty actively when you drop acid on it. A third problem is that fresh, dry wood ash is chemically unstable. You can expect it to go through some difficult-to-predict changes when you put it under water. Yet another problem is that parts of it are soluble and will quickly end up mineralizing your water. Of course, there's some overlap between these problems, but I think you get my drift.

All-in-all, wood ash isn't very inert and isn't very benign. Experiments are always fun and usually worth doing for the learning experience alone, so I rarely try to discourage them. This is an exception. I have a hard time imagining that anything good could come from using fresh, dry wood ash in your substrate.

On the other hand, wood ash can make a pretty good amendment for soils that are low in mineral content and have a low pH. You just spread it out and dig it in.

If you want an inexpensive substrate that's known to work there's always dirt. If you're willing to sacrifice a little cost for some added manageability then there's kitty litter or kitty litter+peat. There are a number of other low-cost alternatives.


Roger Miller

"The indispensible first step to getting the things you want out of life is this: Decide what you want" -- Ben Stein


----------



## HanshaSuro (Jun 22, 2004)

Thank you, Roger. You confirmed what I was afraid of in the back of my mind.


----------

