How To Use Wood Ashes In The Garden: Tips and Precautions

Is it safe or advisable to use wood ashes in your garden? While there are benefits, you’ll want to know these tips and precautions before applying.

Do you heat with wood or have access to wood ashes and wonder if they are a good garden additive? I’ve had a number of people over the years ask how to use wood ashes in the garden. While most of our garden’s additives come from the compost/mulch we apply over newspaper, we do add a bit of wood ashes to our compost pile that I use in planting holes.

While wood ashes are a great source of potassium, they are also highly alkaline (high pH) – similar, actually, to household bleach, believe it or not. This means that you don’t want to add too much and you don’t want to add them around acid-loving plants.

Why Use Wood Ashes

• In addition to potassium (potash) wood ash contains lots of micronutrients, including phosphorous, boron, and calcium (calcium is often lacking in many soils and fertilizers).
• They can even improve the structure of soils.
• Sprinkling ash straight onto the soil also may deter slugs and snails, thought when it gets wet the effect vanishes.

How to Use Wood Ashes in the Garden

For those with naturally acidic soils, you can use larger amounts on lawns and gardens as a substitute for lime. But if your soil is alkaline, you’ll want to go easy on it and just add a little a couple times a year.

If you’d like to add it directly to the garden or who have a lot of ashes to use up, here are some tips and precautions for using wood ashes in the garden:

• Apply the recommended amounts to moist soil and rake lightly to mix, remembering to wear protection. Recommended amounts can be determined by a soil test, but usually a 5-gallon pail over 1,000 square feet is considered safe. With ashes, it’s always better to add less rather than more.
• Use ashes from regular wood only- not treated wood, trash, coal, or briquettes which can contain substances that will inhibit plant growth.
• Don’t use wood ash where potatoes will be planted- they’ll get scab disease if the pH is too high.
• Since it’s alkaline, don’t spread ashes around acid-loving plants such as blueberries, azaleas, and rhododendrons.
• Always rake or mix ash in – if left in piles, excessive salt from the ash can leach into the soil.
• Also, wait until after seeding to rake ashes in- ash contains too many salts for seedlings.
• For a lawn, wait at least a month after wood ash application before applying nitrogen fertilizer to allow time for the soil to reduce the alkalinity of the ash.
• Keep the ashes dry – potash is very soluble, so if your ashes get wet it will all leech out and you’ll be left with a slimy substance.

For us, we’ve always just added our ashes from heating our home in the winter to our compost pile, which is a slow, “cold” breakdown at our place. Meaning we don’t mess with our compost- we simply make a pile of house and garden debris, layered with some leaves and shredded paper, and when it gets big we start a new pile and let that one decompose on it’s own over time. We might mix it once or twice, but that’s it.

For more information about using ashes in our yards and gardens, visit the OSU Extension Service website.

Do you use ashes in your garden? Do you think they’re helpful or harmful?

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