Using Fireplace Ashes in the Garden

fireplace ashes in gardenWinter is officially here, with weather forecast encouraging us to take “Old Man” seriously. And won’t hot soup on the stove and a fire in the fireplace be so good?!

Not every living space can accommodate a fireplace though, so for those who don’t have one read on anyway – that friend with a fireplace may thank you later!

Unless you harvest your own firewood, and even if you do, burning wood that isn’t well cured or dry can make a stove or fireplace burn less efficiently and cause creosote buildup in the chimney. Some experts suggest cutting or buying wood 12 months ahead of the season so it has plenty of time to cure.

Stacking firewood properly and keeping it dry are important considerations, along with choosing wood that burns more efficiently. The rule of thumb for fireplace fuel: hardwoods i.e. hickory, oak, maple, and cherry burn with more energy than softer woods such as pine. Hardwoods are denser, burning longer and cleaner, cutting down on trips to the wood pile and buildup in the chimney flue.

After those cozy fires are out, cleaning the fireplace results in buckets of ash. The question: can those ashes be safely added to the garden, flower bed, or around trees and shrubs as fertilizer? It stands to reason since wood ash is high in phosphorus, the “P” in NPK fertilizer blends containing N (nitrogen), P (phosphorus) and K (potassium), standard in the lawn and garden industry. However, since wood ash, while it adds nutrients to the soil, tends to be alkaline in nature, raising soil pH. Bottom line, wood ashes act like a liming agent, reducing soil acidity. Where a soil report indicates a pH too acid that needs to be raised, wood ashes are one solution. For plants that prefer or need an acid soil; blueberries, azaleas, rhododendrons, Mountain laurel, Oakleaf hydrangea, most hollies, magnolias and many others, wood ashes should NOT be applied.

However, If your soil is low in phosphorus (the ‘P’ on fertilizer bags) and needs to be raised, it can be improved through the judicious addition of wood ash. Usually applied in early spring, when soil is dry and before plants are actively growing, till or incorporate it thoroughly into the soil, being careful to avoid piles of ash that could cause a harmful buildup around plants. A soil test will determine how much phosphorus (P) should be applied, although many garden experts recommend not using more than 20 lbs per 1000 square feet to avoid toxicity issues. Keep wood ash away from seedlings or plant roots which could damage roots. These recommendations are for wood ashes only, not for coal or charcoal ashes or chemically treated wood.

By the way, what exactly does phosphorus (‘P’) do for our plants? Gardeners associate the lack of flowers (and resulting fruit or vegetables) with a phosphorus deficiency. If plants are small, producing little or no flowers, have weak root systems (harder to determine unless the plant is dug up), or have a purplish cast to the leaves, soil could be lacking in phosphorus. A soil test is the best way to confirm a diagnosis, plus a soil test from Auburn’s soil lab will provide a measurement of the deficiency and how to correct it.

Use those wood ashes from the fireplace, but with caution so no harm is done to turf grass, flowers, or vegetables.

By Sallie Lee, Urban Regional Extension Agent, Alabama Cooperative Extension System.  Contact Sallie at

The Alabama Cooperative Extension System (ACES) operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities. ACES is committed to affirmative action, equal opportunity and the diversity of its workforce.  Educational programs of ACES serve all people regardless of race, color, age, sex, religion, disability, sexual orientation, or national origin.

Alabama Extension

The Alabama Cooperative Extension System operates as the primary outreach organization for the land-grant functions of Alabama A&M and Auburn Universities and answers home-gardeners' questions each week on Birmingham Gardening Today.

2 thoughts on “Using Fireplace Ashes in the Garden

  1. Since it has a liming agent can this also be safe for pets to walk on. The reason I asked is because I use lime in the dogs yard to keep dog poo at a minimum if I happen to miss, and it does do wonders for their yard. I burn limbs in a chiminea and often just put the ashes in a bunch in one spot. Usually washes away and heard it was okay for the environment.

    • Carol,
      While I can’t comment on your specific situation, generally yes ashes would be safe for pets to walk on. You might spread the ashes out instead of just one spot, perhaps along one edge of the dog yard. And yes the ashes will wash away with rainfall. Is there any unusual activity downstream of where the ashes are dumped that could be attributed to a buildup of potash? If not, appears environment is absorbing residue without a problem.

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