Wood ash in amendment

The wood ash are an interesting addition to the garden, whether in the orchard, vegetable garden or for ornamental plants.

Need to know what we’re doing…

Wood ash interests

The ash contains a lot of calcium. What makes it an excellent limestone amendment able to replace lime to counteract soil acidity.

Like comfrey, their potassium content is high (between 2 and 9%); they therefore form a concentrated potassium fertilizer very beneficial for the production of flowers, fruits, fruits and root vegetables.

They also include:

  • a lot of silica (14%);
  • magnesium (1 to 4%) which is the main component of plant chlorophyll;
  • low in phosphorus (0.5 to 2%). For example, to increase the phosphorus richness of the ash (allowing the contribution to be rebalanced), the bones from cooking (they contain more than 10%) can be calcined in a wood-burning stove or a fireplace insert with a closed hearth.

Note that the ash from deciduous trees is generally richer than that from the combustion of softwoods.

Using wood ash in the garden

on the grass

The lawn appreciates ash which, in the indicated dose, promotes the activity of micro-organisms and earthworms, which improves water infiltration and thus limits moss. The ash itself does not destroy the moss, contrary to popular belief.

In the vegetable garden, in the orchard, in the ornamental garden

In the natural vegetable garden, ash is good for most vegetables, in the indicated dosage (see below).

Roses also appreciate it, as do flowers, berries, fruit trees, and most perennials and ornamental shrubs.

on compost

A few handfuls of wood ash incorporated into the compost will enrich it with potassium.

No wood ash for acid-loving plants

The high calcium content of the ash (the pH is 13) is not suitable for plants in heathery or acidic soils: azalea, rhododendron, camellia, summer heather, Japanese maple or blue hydrangeas… they will turn pink.

Against snails?

An ash barrier around sensitive plants to protect them from snails is not the best solution.

At the least rain, it forms a crust that subsequently allows the passage of mollusks.

So we have to put it back. This leads to too much ash spreading with the likely consequence of a chemical imbalance and ultimately suffocation of the soil. The exact opposite of what we look for in organic gardening!

Does the ash need to be sieved?

Yes, if there are large pieces of charcoal in it, nails….

No treated wood

To use only ash from untreated wood.

Transport painted wood, plywood, particle board, or other wood that has been treated with chemicals to the recycling center.

Never use soot or coal ash, they are very poisonous.


Given the high content of calcium and potassium, ash should be added in moderate amounts.

Any excess causes a chemical imbalance in the soil and poor plant nutrition:

  • An excess of potassium results in poor absorption of magnesium and other essential elements;
  • The excess of calcium causes a blockage of essential trace elements and the absorption of iron (chlorosis). Even worse, it leads to the destruction of soil humus and the release of nitrogen in gaseous form.

Thereby, adding wood ash is not recommended on calcareous soil (I remind you that ash has an average pH of 13).

Wood ash is good for the garden on acidic or neutral soils, but in limited quantities: 70g to 100g per m² and per year, ie two large handfuls.

Spread of wood ash

Spread the ashes preferably from November to March/Aprilie more or less during the heating period.

But it’s also no problem to apply it later (just before a crop, or even between rows of crops that are already standing), as long as you don’t exceed the maximum amount.

The ash remains on the surface of the soil and destroys the structure of the earth, which can then suffocate.

I therefore recommend yourecord on the surface (on a maximum of 5-10 cm) due to light scratches.