How to Use Wood Ashes in Organic Gardens

Wood Ashes in History

Wood ashes have been used as a garden amendment since before the time of the Romans, for the wood when burned releases gases, but the powdery ashes that remain are still plant material. They are full of micronutrients plants need, including calcium, potassium, phosphorous, and trace elements. Before chemical fertilizers were developed, potash, or "pot ashes" swept from hearths used for cooking, were one of the main sources of fertilizers. The path from pot ashes to good garden soil gives new meaning to the idea of "ashes to ashes, dust to dust."

Before commercial toilet soaps were available, families made their own soap using lye, made from wood ashes soaked in rain water, boiled with rendered animal fat, either tallow, from cattle fat, or lard, from pig fat. Homesteaders and colonists who were among the first Europeans to settle in North America kept a lye barrel going, adding ashes periodically, and would boil soap out doors after rendering the fat, a foul-smelling process where the fat was cleaned and separated from the remains of meat and body tissue that clung to the fat after the animals were butchered for food.

Journals from the 19th century, such as Roughing It in the Bush by Susanna Moodie, an English gentlewoman married to an impecunious and landless younger son of English gentry, document the process. Moodie and her husband immigrated to Canada in the 1830's, drawn by the dream of owning their own land in the New World, quite unprepared for the physical labour and privation required to clear land, build a cabin from trees and sod, plant a garden, make or grow everything they used, and survive or die without medical care or even close neighbours. The book makes a fascinating read, and is full of odd recipes for household staples like bread from bran sourdough, soft soap, and smoked bacon. True to the pioneer spirit that still captures the imagination of many North Americans, back-to-the-landers, and survivalists, some of these recipes are circulating on websites like this one if you want to try making soap from ashes yourself.


Add small amounts of wood ashes to compost to alkalize the soil and add calcium, phosphorous, potassium, and other nutrients plants need.
Add small amounts of wood ashes to compost to alkalize the soil and add calcium, phosphorous, potassium, and other nutrients plants need. | Source

pH of Common Products

pH
product
14
commercial lye or caustic soda (sodium hydroxide NaOH)
13
wood ash lye (KOH)
12.4
lime
111
ammonia
8.3
baking powder
7.4
human blood
7.0
pure water
6.6
milk
4.5
tomatoes
3.0
apples
2.0
lemon juice
0
hydrochloric acid (HCl)

Ashes for Gardens


When ashes mix with water they create potassium hydroxide, a form of lye. Lye is a strong base, and it raises the pH of soil chemistry to make soils alkali. Most plants thrive when soil pH ranges between 6 and 8. Some plants, such as blueberries, cranberries, rhododendrons and azaleas, prefer acid soil around 6.4 pH. Other plants prefer more alkali soil. Consequently, adding ashes to your garden may be useful depending on the chemistry of your soil. It is especially useful n rainy climates, where acid rain makes soil acidic, and on properties where there are many pine needles in the soil, or oak leaves, since these are acidic.

Since the ash particles are fine, and dust-like, they mix easily into the soil. They are light, so don't spread them on a windy day, when they easily blow around. Avoid breathing them in.

To deter snails and slugs from your plants, try circling plants with a ring of ashes. When they creep toward the new shoots and leaves, the ashes dry out their skin, and send them in another direction.

Soil pH Affects Plant Health

pH
Plant
7-7.5
dianthus, boxwood, aucuba, daphne, lilac
6.5 and higher
pink flowers on hydrangeas
6.0-7.0
most vegetables
6.0-6.5
roses
5.5-6.5
most fruits
5.5-6.5
purple flowers on hydrangeas, or mixed pink and blue
5.5 and lower
blue flowers on hydrangeas
5.0-5.2
potatoes
4.9-5
blueberries
4.5-6
rhododendrons
Amend the soil to suit the plants you want to grow, or choose the right plant for your conditions. Manure makes soil acid; wood ash and lime make soil alkali.
Add fresh grass clippings to compost for nitrogen and heat.
Add fresh grass clippings to compost for nitrogen and heat. | Source

Ashes for Plants

Since wood ashes come from plants, they have many of the micro-nutrients plants need. They are a good source of calcium, potassium, phosphorous, magnesium, and trace elements. Their chemical make-up is equivalent to about 0-1-3 (N (nitrogen)-P (phosphorous)-K (potassium). Plants need calcium to develop strong roots, cell walls, and to complete protein formation. Potassium is necessary in photosynthesis, or the process during which plants manufacture food in green leaves in the presence of light. Potassium is also required for moving sugars, forming seeds, synthesizing proteins, and using nitrogen.

Occasionally layer the compost with small amounts of wood ash between greens and browns.
Occasionally layer the compost with small amounts of wood ash between greens and browns. | Source
Coffee grounds are browns for compost, a good source of carbon.  Get them for free from your local coffee shop.
Coffee grounds are browns for compost, a good source of carbon. Get them for free from your local coffee shop. | Source

Fireplace Ashes for Compost

Adding small amounts of fireplace ashes to the compost helps maintain a neutral pH in the composter, to allow the active microorganisms to function most effectively. Use it sparingly, and sprinkle it on layers: a layer of green (grass clippings), a layer of brown (sawdust, dry leaves, coffee grounds from your local coffee house, or vegetable scraps), and then a light layer of ashes. For best compost, aerate the pile every few days by turning it with a compost turning tool. Keep the pile moist, but not wet. If necessary, add water. Compost that is working effectively gets very hot, has steam rising off it, and feels uncomfortably hot if you put your hand in.

Be sure to keep within the recommended quantities, for too much ash raises the alkalinity of the soil and accumulates salts that will harm your plants.

Ashes as Fertilizer

Mix wood ashes into your organic fertilizer instead of ground limestone. Recommended quantities are about 20 pounds (5 gallons) of ash/1000 square feet of garden/per year, which is equivalent to about 6 pounds of ground limestone in the same area.

Try this organic fertilizer recipe:

4 parts seed meal (alfalfa, soy, cotton, or canola--whatever is available in your area)

3 parts wood ashes or 1 part Dolomite lime

1/2 part kelp meal

1/2 part bone meal




In an organic garden, this compost turning tool with folding flanges at the point is an effective way to aerate compost and speed up the decomposition.
In an organic garden, this compost turning tool with folding flanges at the point is an effective way to aerate compost and speed up the decomposition. | Source
Compost is an essential part of the organic garden.  Layering greens and browns, adding a little firplace ashes to compost, and turning every few days with the compost tool help.  The flanges fold to penetrate compost, then open to lift and aerate.
Compost is an essential part of the organic garden. Layering greens and browns, adding a little firplace ashes to compost, and turning every few days with the compost tool help. The flanges fold to penetrate compost, then open to lift and aerate. | Source

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Comments 6 comments

GoodLady profile image

GoodLady 4 years ago from Rome, Italy

Another Gem. Thanks for so much useful information and telling us about the book 'Roughing it in the Bush' which I will order if I can find it - and I'm sure I will enjoy reading.


Janis Goad profile image

Janis Goad 4 years ago Author

Hello GoodLady! What do you do with the fireplace ashes from your farmhouse in Tuscany? I read in one of your hubs that you heat your home with wood fires in winter, and in spring have to clean all the fireplaces.

Roughing It in the bush is worth the read. Immigrants even today come to Canada and U.S. looking for a better life, but it is hard. Many of them stay for their children, or because there is no way back. I am fascinated by the lore of early pioneers, and amazed by what they survived.


Ruby H Rose profile image

Ruby H Rose 4 years ago from Northwest Washington on an Island

That explains why the hole I filled in my yard with ashes is growing so bountifully with grass now! Wonderful hub, thanks for all the great information. Shared for sure.


Janis Goad profile image

Janis Goad 4 years ago Author

I think you must have a beautiful garden, Ruby Rose. Thanks for the visit.


Janis Goad profile image

Janis Goad 4 years ago Author

I think you must have a gorgeous garden, Ruby Rose. I love the hub you wrote about your grandmother's garden!

Thank you for reading and taking the time to comment.


The Dirt Farmer profile image

The Dirt Farmer 4 years ago from United States

Useful info, Janet! Thanks.

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