Clever Ways to Use Wood Ash in the Garden

For many gardeners, wood ash is a plentiful and free resource. If you burn wood, you surely have plenty of wood ash that needs somewhere to go. Even if you don’t burn ash to heat your home, you may have a friend or neighbor who might be happy to let you clear away their ash and put it to good use in your yard or garden.

Why Wood Ash?

What does wood ash do for your garden?

Wood ash is a useful fertilizer and amendment that can be used in the garden, on lawns, and in landscapes, too. It is a good source of several important minerals and nutrients for your yard and garden. It is also a highly effective amendment for modifying soil pH.

The most abundant mineral nutrient in wood ash is calcium. On average, the calcium content of wood ash is 20% or higher. Calcium is an important element that helps plants stave off diseases such as the notorious blossom end rot.

Wood ash is also a very good source of potassium—it is about 5% potassium. It is commonly known or referred to as “potash” for this reason, and potassium is the mineral that wood ash is most often used for. When people look for a source of potassium, they look to potash—wood ashes.

Other minerals found in wood ash are magnesium, sulfur, and phosphorous, all found at concentrations around 2%. In addition, wood ash contains trace amounts of manganese, iron, zinc, aluminum, boron, copper, and other trace minerals.

Besides being a source of potash, wood ash is also commonly used as an amendment to adjust soil pH. The high calcium content in wood ash is in the form of calcium carbonate. Calcium carbonate is what is in agricultural lime. One of the major uses of lime in gardening and landscaping is in raising soil pH to reduce its acidity and make it more neutral or alkaline (depending on the goal and how much is used). This makes wood ash an excellent, free resource for amending acidic soils or soils with a low pH.

How To Use Wood Ash in the Garden or Landscape:
Wood ash is very easy to use for the lawn and garden. The key lies in knowing when to use it, how much to apply, and what it is and isn’t good for.

When Should I Apply Wood Ash to my Garden?
Wood ash is a good annual soil amendment and fertilizer as long as it is not used on the “wrong” plants. The best time of year to apply wood ash to your garden or yard is over the course of the winter or in the early spring.

Look to wood ash when you need to add potassium (potash), sweeten acidic soil, and/or increase levels of calcium or phosphorous.

Fortunately, wood ash works relatively fast and so it can be applied almost up to planting time (and in some instances, as a top dressing or side dressing). For best results, it is recommended to apply it at least a month before planting.

When used as an amendment to adjust soil pH, wood ash only needs about a month to work. It works much more quickly than lime, so if you have missed your window and need a quick fix for soil pH, wood ash is a better choice.

As a rule of thumb, it is not recommended that you apply wood ash to soils that have a pH level of 6.5 to 7 or higher because it will make the soil too alkaline; however, that depends on how high a pH you are trying to achieve. If a more alkaline soil is the goal, wood ash will still be an option.

Ash can be used in place of lime for lawns as well. You will need to adjust the application rate to achieve the desired results (see the section on application rates below).

How Do I Apply Wood Ash to my Garden?
“Safety first” applies to using wood ash just as it would for any other type of fertilizer or amendment.

The first rule is to make sure that the ash you are spreading is well cooled and is no longer burning. Be aware that when ash is piled or bucketed when still hot the inner layers can hold heat and smolder for quite some time—days even. Avoid handling or spreading hot ash. Take care not to burn yourself and be especially careful if you live in a dry or fire-prone area.

If the ash you are using has large coals or chunks of unburned wood in it, sift the large pieces out before you spread it on your lawn or garden. This can be done by simply pouring the cool ash through a screen of one-quarter or one-half inch hardware cloth.

Wood ash is obviously quite light and can be irritating to the eyes, nose, respiratory tract, and to bare skin.

It is wise to wear safety glasses or goggles, long sleeves and long pants, gloves, and a mask or covering for the nose and mouth when you are applying wood ash. Avoid breathing in ash and do not spread ash on a windy day (not only is this less safe, but you may end up wasting this valuable amendment and fertilizer if it blows away).

Spread wood ash evenly and do not leave large clumps or piles which can result in too many salts concentrating in one area. Up to a half inch of ash is fine. Note that as an amendment to help improve soil tilth, heavy clay soils can take more ash than sandy soils can.

It is best to apply wood ash onto moist soil so that it stays where it is needed. If that is not possible, you may want to sprinkle or water the area after application. If spreading on loose soil, work the ash in as soon as possible to maximize its benefits.

How Much Wood Ash Should I Use in my Yard or Garden?
The application rate for wood ash will vary slightly depending on where you are using it and for what purpose.

Wood Ash Application Rate for Gardens and Flower Beds

In the garden, the application rate for wood ash is between 15 and 20 pounds per 1,000 square feet. This is roughly equal to the amount of ash that you will get from burning one cord of wood.

A five-gallon bucket holds about 20 pounds of wood ash. So, to make it easy, use one five-gallon bucket of clean wood ash for every 1,000 square feet of ground.

If you are applying ash as a top-dressing fertilizer or amendment around individual bushes, spread one-half to one pound evenly around the base of the bush.

For individual plants, sprinkle no more than one-half inch thick around the root area at the base of the plant.

For larger trees and fruit trees, apply to the area of the base of the tree to a thickness of one inch deep.