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Using Ash in Organic Gardening

Wood Ash for Organic Gardening

Bonfires may be a contentious issue, what with smoke and global warming. Here in Thailand though, they love them.  Thai’s burn everything from kitchen wastes, to yard trimmings and the remnants of rice & sugar cane crops. Reservations aside, a fire gives you the great satisfaction of getting rid of perennial weeds, branches too thick for the shredder, and diseased material while, at the same time, producing a valuable by-product: ash.


Wood ash (as opposed to coal ash) can be a great addition to the garden. It contains potassium or potash (they’re not identical but – scientists look away now – the terms are often used interchangeably), and potassium is a vital nutrient for crops.

Just as it does in humans, potassium regulates plants’ water balance (so tissue is firm and juicy), and has a part in transporting food within the plant and creating sugars and starches. Without enough, vegetables are more vulnerable to drought, frost, pests and diseases.

20161019_093032Add Ash to the Compost Heap

Wood ashes make a great addition to the compost heap, where they’ll aid fertility (most of the nutrients needed by plants are contained in them to some degree). If you have a lot, don’t add them all at once as they are alkaline and raising the pH too much will affect the bacteria and worms at work. It’s better to keep the ash in a nearby container and sprinkle on a layer every so often.

If you tend to compost a lot of acidic material, such as fruit waste, the ashes will help to keep the compost at a lower pH and reduce the need to lime the vegetable plots at a later date.

Wood Ash as a Substitute for Lime

Speaking of liming, because ashes are alkaline, it is possible to substitute them for the usual ground limestone. However, home-produced ash isn’t a standardized product, which means its content will vary.

Hardwoods, for example, generally produce more ash and contain more nutrients than softwood. According to the very thorough information from Oregon State University Extension Service, ash from a cord of oak will provide enough potassium for a garden 60 x 70 feet, whereas a cord of Douglas Fir will be sufficient for a garden 30 x 30 feet, while both will raise the soil pH slightly. Bonfire ash is even more variable, because of the mix of plant tissue.

Like the potash content, the calcium carbonate content will also vary (although it’s unlikely to contain more than half that of ground limestone), so it’s a good idea to test the pH of your soil before adding the ash and three to six months after, to check on its effect. It wouldn’t hurt to check up on the potassium content while you’re at it. There’s no point in adding potash to a soil that’s already high in potassium, as too much can affect the plants’ take-up of other nutrients.


Did you know that you can use wood ash in the garden? Yes you can!

As a matter of fact wood ash is beneficial to your garden. It can act as an organic soil booster and as a pest repellent. So if you have wood ashes from your summer campfires, backyard firepits, fireplace or wood stove, do not throw these, instead use them in your garden.

Wood ash is a good source for calcium, magnesium, phosphorus, and potassium that can encourage stem growth and strong roots.

The main benefit of wood ash in the garden is that it increases the alkalinity of the soil, which is helpful if your soil is acidic. Wood ash is also considered as a good alternative for lime because it can sweeten the soil. Wood ash also produces faster results than lime because it is more water soluble.

20161019_093038How to use wood ash?

Scatter wood ash on top of the tilled dirt and then mix it using a rake. Break down any clumps because a heavy concentration can cause damage in your soil. It may result in a potentially harmful salt spot when it gets wet.

Apply wood ash about 3 weeks before planting. Make sure that the dirt is dry and apply when it is not windy.

Amount of wood ash to use:

Use not more than 25 gallons of wood ash in every 1,000 square feet per year. Don’t forget to test your garden soil before applying.

You can still scatter wood ash even if you have already planted; just sprinkle some wood ash around your growing plants. You can apply it in your flower beds, vegetable garden, around your shrubs and in your lawn.


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