Mixing ash with your garden soil?

By The Helpful Engineer / On / In Technical & Discussion

Wood AshWhat to do with your wood stove ash?

Well I usually rake it into my garden as it seems a waste to throw in the black or brown bin. But this was only after a bit of trial and error. At first I didn’t mix it in and it then formed a grey lump which looked a bit like soft concrete. It turns out that this is caused by the calcium in the ash which usually makes up 25% of wood ash.

But I was reading a book last night which gave me a bit of a fright, it said that in general trees absorb heavy metals from polluted soils and these will remain in the ash after burning.  Understandably this led me to doing a bit of  extra research, and from this the main points of note are:

  1. Its seems to be fine to add wood stove ash to the garden once its well mixed in, but over time the ash will raise the Ph of the soil so its not ideal for acid soil loving plants. Turf ash also seems to be fine, which is still an important fuel for many Irish people.
  2. Its best not to add wood ash to soil if you are planning to grow fruit or veg as it may cause difficulties with yields/pests.
  3. Coal ash shouldn’t be mixed with soil.
  4. Wood ash will act similar to a weak soil fertilizer and contains mainly calcium, approx 10% potassium, approx 2% phosphorus and no nitrogen. Therefore if comparing it to a standard N-P-K  fertilizer its make up would be 0-2-10. These are loose figures as the actual make up of the ash depends on the wood burned.
  5. Hardwood ash has more nutrients than softwood and produces more ash.
  6. Ash is a good slug and snail repellent if left on the surface.


Here is a website that promises 30 uses for ash! Click here for link.  You can even make soap with wood ash!

One thought on “Mixing ash with your garden soil?

  1. Reduced heat of hydration. Replacing cement with the same amount of fly ash can reduce the heat of hydration of concrete. This reduction in the heat of hydration does not sacrifice long-term strength gain or durability. The reduced heat of hydration lessens heat rise problems in mass concrete placements.

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