March 6th, 2012

Wood Ash as a Compost Ingredient

I’m not sure what to do with all my excess wood ash from the fireplace. I need to lower my soil pH, so I can’t add the ash to the garden or compost.

blog-dougThe ash from a wood-burning fireplace contains nutrients that plants need, including potassium, calcium, and trace amounts of zinc, magnesium, and phosphorus. But those nutrients come with a warning: Wood ash is strongly alkaline. If added to soil, it will raise the pH, or the measure of a soil’s acidity or alkalinity. Where the soil is too acidic (pH too low) and a higher pH would be beneficial, wood ash can be applied to lawns or gardens in place of agricultural lime to raise the pH. But if you are dealing with a neutral or alkaline (high pH) soil, adding wood ash would be a mistake.

The same goes for adding wood ash to a compost pile. Consider including wood ash as a compost ingredient only if the pile contains significant quantities of acidic materials, such as shredded oak leaves or pine needles. Even then, apply the ash with restraint, because too much can result in a loss of nitrogen from the compost. At a higher pH, the nitrogen present in the compost pile will escape to the air as ammonium hydroxide; if you smell ammonia near your compost pile, it’s losing nitrogen.

If you decide you shouldn’t use wood ash in your garden or compost, and you can’t find a farmer or gardener who can use it, I suggest you send the ash to a landfill with the rest of your household waste.  —Doug Hall

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Comments

    Doug, I enjoyed reading this article, but I found the last sentence to be a bit disconcerting. That is, you recommend the individual try 2-3 options, and if those don’t work, then give up and send the organics to the dump? Really?

    There has got to be an option 4, and if that doesn’t work, an option 5, 6, 7, and so on…

    Here are some additional suggestions…

    - call your local garden centers and ask if they can use them.
    - call your nearest compost facility and ask if you can drop them off
    - Use them as an ice melter
    - Use them to control pond algae
    - Make soap

    Below are a couple references for additional ideas (I have no affiliation with the sites below, they’re just helpful bits of advice):

    http://www.thisoldhouse.com/toh/article/0,,1581470,00.html
    - http://www.greenlivingtips.com/articles/255/1/Uses-for-wood-ashes.html

    Thanks.
    d

    Good information, I use some (not too much!) wood ash in my compost and it works fine, makes great compost tea!

    What about some of the leftover ‘charcoal’ (wood, not those briquette things)? Would that be a good compost item? Are they also highly alkaline?

    Wood ash is a completely natural ingredient and you are making a mountain out of a molehill. Obsessing about pH, especially since it is on a logarithmic scale is as bad as turning down free hay because there might be weed seeds. Penny wise and pound foolish. Get out of the “soil test” mindset and you will do a better job of buildng your soil.

    Compost pile microorganisms cannot digest ash. So if you need to raise the pH in your garden soil, it’s best to add AFTER composting.

    My wife had a couple of Boston ferns about ten yrs old out on the back patio. I was distributing the rest of last winter’s ash and ended up with just a light dusting in my bucket. I added a gallon or so of water, swished it well and dumped it on the ferns. Heck, they needed water. It was hot and dry. Within a week both were dead as dust.
    From now on I’ll limit where and how much I’ll use!

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