Thursday, 13 November 2014

Wood Ash: Natural Fertliser for the Ecological Garden/Farm

As winter approaches we are again lighting fires in our household that provide us with a weekly supply of wood ash which, as this post will describe, can make an excellent additive within the ecological garden/farm.    

Wood Ash: Potassium Fertiliser 

Ash from wood fires, such as bonfires or wood burning stoves, provide a natural source of potassium (K) and other trace elements. Potassium is a major plant nutrient associated with flowering and fruiting. The levels of potassium in ash will vary depending on the age of the wood that was burnt; young wood from pruning will have higher potassium content than older, thicker branches.


Wood Ash: Raising  pH

Soil pH is the measure of the acidity (sourness) or alkalinity (sweetness) of a soil. A simple numerical scale is used to express pH. The scale goes from 0.0 to 14.0, with 0.0 being most acidic, and 14.0 being most alkaline. The value, 7.0 is neutral - i.e., neither acid or alkaline.

Applying wood ash to your soil will raise the pH, reducing the acidity of soils. The majority of vegetables grow best in soils with a pH of 6.5, so testing the level before adding the ash is recommended so as not to raise the pH too much (greater than pH 7.0). However, where club root is present, wood ash can be used to raise the pH to as much as 7.5 to inhibit this disease and still provide good conditions for plant growth.
Intensive vegetable production tends to push soils to the acidic side of the scale, so the addition of ash can help to keep pH at optimal levels whilst providing essential nutrients to your plants.

Most fruits perform best in slightly acidic soil so be aware of the current soil pH and optimal pH of your fruits before applying ash. High pH can be detrimental to acid loving fruits such as blueberries and cranberries. Below is a list of optimal pH ranges for some common fruits and vegetables.  

Table showing optimal pH range for Fruits and Vegetables 

When to use wood ash

If applying wood ash directly to soils, do this in the winter and rake or dig it in lightly to allow the compounds in the ash (which could scorch plants) to react with the moist soil and be rendered harmless before spring sowing or planting.

You can use wood ash in your compost piles at anytime of the year, applying a sprinkling on top of every 15 cm of material. Heavier use risks the presence of high levels of alkalinity and soluble salts which could damage both plants and the soil.

Wood ash can also be used to reduce the acidity in a worm farm. Worms dislike acidic conditions and prefer neutral pH (7). They will stop breeding and start to migrate from the farm if acidic conditions persist. How much ash you use is determined by the size of your worm farm  and the current pH. Having a pH reader and experimenting with quantities of ash is a good way to maintain optimal conditions in the worm farm.  

How to use wood ash

Wood ash can be spread directly on soil in the vegetable garden in late winter at a rate of 50-70 g per sq m; Fork in, rake over or add to chicken tractors and the chickens will work it into the soil for you. It may be useful to sieve the ash before use to remove debris.

Where wood ash is applied frequently to the vegetable plots, it is worthwhile to use a pH test kit to monitor changes in pH and prevent levels rising over pH 7.5
Never leave wood ash in the rain, as the potassium (a useful plant nutrient for flowers and fruit) is in a soluble form and is easily leached out
Apply wood ash in small amounts to the compost heap where, once mixed in, it will blend readily with other materials. As a general guide, you should not be able to identify it after mixing it into the compost.

Things to consider 

  • Avoid using too much wood ash as an excess in alkalinity can be detrimental to some plants.
  • Avoid using ash from treated timber as they may contain potentially harmful residues.
  • Avoid using wood ash on areas where potatoes are to be grown the following spring, as the alkaline conditions can encourage potato scab
  • Ash from coal or anthracite has little or no nutritional benefit and is potentially harmful to soil, plants and consumers of edible produce. 
  • Ash from lump wood charcoal can be used as recommended for wood ashes. 

We offer a range of plants and seeds for permaculture and forest gardens from our plant nursery including a new range of fruit and nut cultivars well suited to natural gardens. Delivery to all over Europe available from Nov - March 





Want to learn how to create regenerative landscapes?  Join us this summer for our Regenerative Landscape Design Course.




 Balkan Ecology Project Bio-Nursery 


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