Wood Ashes in the Garden: Good or Bad?

One of the things I love the most about cooler weather is the nice cozy fires that my husband builds in our fireplace and outdoor fire pit. Whether it’s because he is a Sagittarius (one of the fire signs of the zodiac) or just because he grew up in a campfire loving family, Tom starts building fires as soon as the temperatures begin to fall.

Needless to say, we end up with a LOT of wood ashes. The first time I cleaned out our fireplace (over ten years ago now) I piled huge buckets full of ashes into our compost pile. It just seemed somehow logical to me, putting decomposed wood back into the earth. Tom, my green-gardening guru hubby, just shook his head. Then he told me to get a shovel and he helped me dig them all back out and put them in a metal container so we could better control their use in our landscape.

I wasn’t WRONG about the nutritional value of wood ashes. The truth is that wood ashes contain most of the 13 essential nutrients that soil must supply for plant growth. The secret is just to make sure that you utilize those nutrients ONLY as needed.

When applied directly to garden soil, wood ashes will raise the pH level. This is great if the pH level of your soil is low. Not so great if the pH level of your soil is already high. In fact, over applying wood ash can cause serious imbalances in your soil.

The pH value is a measure of a soils acidity or alkalinity and directly affects the ability of plants to utilize the nutrients available to them. The pH scale ranges from 0 to 14, with 7 as neutral. Numbers less than 7 indicate acidity while numbers greater than 7 indicate alkalinity.

So how do you determine the pH value of your soil? You get your soil tested.  Getting your soil tested is an excellent way to help minimize the use of chemicals in your yard. Knowing what your yard needs allows you add only what is necessary, eliminating the possiblity of harming your yard or causing excess nutrients to find their way into our waterways.

If the pH level of your soil is low, then adding wood ash may be beneficial. Again, this depends on what you want to grow. Wood ash is beneficial to most garden plants except acid-loving plants such as blueberries, rhododendrons and azaleas.

Here are a few more facts about wood ashes, I found from searching usasearch.gov:

The value of wood ash depends on the type of wood you burn. Harwood ash has a higher percentage of nutrients than ash from softwoods.

Lawns that need lime and potassium can also benefit from wood ash but you should apply no more than 10 to 15 pounds of ash per 1,000 square feet of lawn and only every couple of years.

Wood ash is alkaline, which means you should use precautions when handling it.

• Wear eye protection, gloves and a dust mask.
• Do not scatter ashes in the wind.
• Do not use ash from burning trash, cardboard, coal or pressure-treated, painted or stained wood. These materials can contain potentially harmful substances. For example, the glue in cardboard boxes and paper bags contains boron, an element that can inhibit plant growth at excessive levels.
• Never leave wood ash in lumps or piles. If it is concentrated in one place, excessive salt from the ash can leach into the soil and create a harmful environment for plants.
• Do not apply ash at time of seeding. Ash contains too many salts for seedlings.

Source: Wood Ashes Can Benefit Gardens and Lawns