Print This Post Print This Post

Wood Ash In My Garden As A Fertilizer

Written by Hilary on January 13th, 2009

At this time of year with the cooler weather, a lot of people want to know if they can, or even should, use wood ash in the garden as a fertilizer, or soil conditioner.

Well, let’s take a quick look at the variables:

1. Wood ashes will raise soil pH because the largest component of wood ash (about 25 percent) is calcium carbonate, a common liming material that increases soil alkalinity. So generally use them only if your soil pH is under 7.0 based on a soil test.

2. The safe rate of wood ash application to lawn or gardens is 15 to 20 lbs. (7 to 9 kg) per 1000 square feet (93 square meters) per year, which is approximately a 5 gallon (19 l) pail.

3. Remember, a little wood ash is beneficial, but a lot is not because increasing the alkalinity of the soil does affect plant nutrition. Nutrients are most readily available to plants when the soil is slightly acidic. As soil alkalinity increases and the pH rises above 7.0, nutrients such as phosphorus, iron, boron, manganese, copper, zinc and potassium become chemically tied to the soil and less available for plant use.

4. Wood ash does have some fertilizer value, the amount varying somewhat with the species of wood being used. Generally, wood ash contains less than 10 percent potash, 1 percent phosphate and trace amounts of micro-nutrients such as iron, manganese, boron, copper and zinc.

5. Trace amounts of heavy metals such as lead, cadmium, nickel and chromium also may be present. Wood ash does not contain nitrogen.

6. Applying small amounts of wood ash to most soils will not adversely affect your garden crops, and the ash does help replenish some nutrients. But because wood ash increases soil pH, adding large amounts can do more harm than good.

7. Crop tolerance to alkaline soil also should be considered. Some plants, such as asparagus and juniper, are more tolerant of slightly alkaline conditions than “acid-loving” plants, such as potatoes, rhododendrons and blueberries. Wood ash should never be used on acid-loving plants.

8. The best thing with wood ash is to use it sparingly, and test your soil pH regularly to make sure you are not causing any problems.

For more Gardening Tips and Gardening Advice visit our main gardening website at Weekend Gardener Monthly Web Magazine –

Have great week!


Related Posts

14 Comments so far ↓

  1. Dwayne says:

    Wood ash is one of those subjects that gets confusing at times. One thing I have always wondered about wood ash is this:

    Lye comes from hardwood ash. Water is seeped through wood ash and the liquid captured and dried. The result is lye.

    When water seeps through the ash on the garden, lawn, or compost heap, there must be some lye produced. I am sure that is what is raising the Ph, but, has any studies been done to find the true results, good or bad?

    I would sure like to find one.

  2. Hilary says:

    Hi Dwayne,

    Yes wood ash can get confusing, but the information I posted above is tested information and the true results are that wood ash has both good and bad results depending upon how you use them.

    As said above, they raise pH which can be good or bad depending upon your garden soil and plants’ needs.

    It’s true that unlike limestone, which can take six months or more to take effect, wood ash has high water solubility and quickly changes the soil pH.

    This can cause a problem with raising the soil pH over the optimum level of 6.5 to 7.0 if too many ashes in spread in the same area.

    As to how much lye wood ashes can make, that really depends upon many factors.

    When ash is produced in industrial combustion systems, the temperature of combustion, cleanliness of the fuel wood, the collection location, and the process have profound effects on the nature of the ash material.

    Therefore, wood ash composition can be highly variable depending on geographical location and industrial processes. This makes testing the ash extremely important.

    Calcium is the most abundant element in wood ash and gives the ash properties that are similar to agricultural lime.

    Ash is also a good source of potassium, phosphorus, magnesium, and aluminum. In terms of commercial fertilizer, average wood ash would probably be about 0-1-3 (N-P-K).

    In addition to these macronutrients, wood ash is also a good source of many micronutrients that are needed in trace amounts for adequate plant growth.

    Wood ash contains few elements that pose environmental problems. Heavy metal concentrations are typically low and not in a highly extractable or available form.

    Lastly, I feel that when using wood ash wisely, you will not have any danger of lye because as mentioned above, using approximately a 5 gallon (19 l) bucket of ash spread over 1000 square feet (93 square meters) per year, is a very thin layer.

    You can’t really compare a very thin layer like that to how much wood ash you need to make lye for soap.

    When using wood ash to make lye for soap, generally 2 or 3 feet (1 m) of wood ash is concentrated into a barrel and the water slowly works its way down and drips lye out into a bucket.

    So I think if used wisely, with good soil testing first and making sure that your soil and plants need the nutrients that wood ash provides, you will be just fine.

    I personally would never put wood ash in my compost pile, but if I burned wood in a fireplace and had wood ash on hand, and I had a very acidic area of my garden, I would use a little of it and then test the soil every year to see what the pH was to make sure I wasn’t creating any problems.

    I hope this answers your concerns.

  3. nick says:

    can i mix the woodash with water to liquidflied and use as fetilizer ?

  4. Hilary says:

    Hi Nick,

    I wouldn’t because they don’t provide balanced nutrition and they can acidify soil so quickly that they could cause more harm than good.

    Get a good organic fertilizer and you will be much better off.

  5. Caroline says:

    I am doing the Science Fair with my daughter, and… we need some help!! We need a reason why we think that fireplash or wood ash will make a good plant fertilizer. I need to go back to foruth grade!

  6. Hilary says:

    Hi Carloine,

    Well I suggest you go back up and read the original post.

    Unfortunately wood ash is not a good regular plant fertilizer, and as mentioned above, should not be used other than sparingly and very carefully after having tested your soil pH to make sure you are not doing more harm than good.

    Sorry, but I think you might have to come up with another topic for your science project!

    Good luck.

  7. Hilary says:

    Or – you can prove with your science project why wood ash is NOT a great fertilizer.

    You can show how it changes the soil pH to alkaline and what plant deficiencies and problems will then develop.

    Good luck!

  8. jamie says:

    Hi, As with most horse owners I have piles of hay and poo i compost some but was wondering if i burnt the hay and poo it just smoulders away would the resultant mixture be ok if mixed up with standard compost?

  9. prabha says:

    i want to develop a fertilizer by using wood ash for tea cultivation in sri lankan wet zone.can i have some suggestion or information related to that?

  10. prabha says:

    what are the considerations that we have to consider,when develop a fertilizer with wood ash for the tea cultivation in wet zone?

  11. Jerry Smith says:

    I have a outdoor wood burner and produce a lot of wood ash! What should I do with it without doing any damage?

  12. joey gerona says:

    i use wood shave mix with clay soil in my ornamental and flowering (roses, rose of sharon, anthuriums,garden mums, green tes, ashitaba) plants…and its just wondering why…there saying its not good for plants

  13. joey gerona says:

    just wash the wood shave let dry before mixing with clay soil….the wood shave is mahogany

  14. joey gerona says:

    i use wood shave mix with clay soil in should try it or experiment..theres no harm on trying….im living in a tropical country…maybe its good to use it in warm climates

Leave a Comment