Potash – Wood ash as fertilizer


Your detailed answer on the use of ashes from our log fire as a fertilizer was very helpful. We live in Rosedale Toronto and have Clay soil. Would this change any of your recommendations as regards the quantities to be applied per sq ft (You suggested 20lbs of log ash per 1000 sq ft?)


Thank you for contacting Toronto Master Gardeners.

Unfortunately, I do not seem to have access to your previous question or the answer that was provided.

As you may have already been told, wood ash can be used to add potassium to the soil and one of the  benefits of wood ash is also to raise the pH of soil or make it less acid.  If your soil already has a pH level of 6.5- 7.0 then for most plants you would not need to raise the pH level.  If you are not sure of your soil’s pH level, there are testing kits available. Clay soil describes its texture and not necessarily the pH level.  More material is required to change the pH level of clay soil compared to sandy soil so in general, clay soils may tolerate more wood ash than sandy soils. pH levels of clay soil can tend to be higher, but if yours is not within the desired range, then wood ash is a good choice. If the pH level of your clay soil is optimal (6.5-7.0) it will be more easily worked and granular.  When pH is low in clay soil it can be sticky and harder to cultivate.

The amount of ash to add will depend on your soil’s pH and the plants you want to grow, but 20 lbs per 1000 square feet is a good general rule of thumb. For a lawn, it is recommended to use slightly less – 15 lbs per square foot.  It is important not to let the ashes clump or remain in piles so that nutrient salts do not damage the roots of your plants.  Another option is to store your dry ash and then make a “tea” by adding water to use for fertilizing during the growing season. This can be done by placing about 3 lbs of wood ash in a permeable or burlap bag, placing it in a 30 gallon pail of water and leaving it for 4 to 5 days.  There are some plants that will not benefit from wood ash, namely those that prefer acid soil such as berries, rhododendrons and fruit trees.

I hope this is a helpful addition to the answer that you already received.

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