We predominantly heat our home with a wood fire which does a bang up job. However dealing with all the wood ash that comes out of it has been a bit of a quandary for us. As a result we’ve had an impressive collection of boxes filling up with ash outside our back door, waiting for one of us to think properly about how we can integrate it into our property rather than putting it in the bin.
Because, while a little bit of wood ash on your garden can be beneficial – a lot of it generally leads to tears as it increases the alkalinity of the soil drastically, affecting the plant’s nutrition. Nutrients are most readily available to plants when the soil reads 7 on the pH chart and wood ash can throw this out of balance, pushing this number up towards 10.
“Since wood ash is derived from plant material, it contains most of the 13 essential nutrients the soil must supply for plant growth. When wood burns, nitrogen and sulfur are lost as gases, and calcium, potassium, magnesium and trace element compounds remain. The carbonates and oxides remaining after wood burning are valuable liming agents, raising pH, thereby helping to neutralize acid soils” (soil scientist, Dan Sullivan).
Of course, the fertilizer value of wood ash depends on the type of wood you burn. As a general rule, hardwoods (i.e. eucalyptus) yield more ash per kilogram of wood burned and contain a higher percentage of nutrients compare to ash from softwoods such as pine.
However some plants, including asparagus, are more tolerant of slightly alkaline conditions compared to acid-loving plants, such as potatoes, rhododendrons and blueberries. Wood ash should never be used on acid-loving plants.
So while it’s well known that you can add small amounts of wood ash into your compost pile and spread some onto your vegie beds (it can help deter slugs from attacking your seedlings), I’ve always wondered what to do with BULK ash. At our place we’re trialing a little experiment in our garden which revolves around our ever useful and multifunctional swale pathways. Rather than putting a little bit of ash here and there, we’re seeing whether we can get away with bulk seasonal integration of wood ash going directly into our sawdust swale paths.
Our swale path’s main job is to catch and store water, but they’re also slow in situ compost piles, meaning that one day, when the sawdust/woodchips have decomposed nicely they will end up on either a vegetable garden or in our orchard. With this in mind, it’s important that they have good mineral profile, we don’t want to mess with it too much, making it significantly alkaline or acidic. Currently we’re comfortable with the ash input, as the ratio of sawdust (mostly from hardwood timber) is high compared to the quantity of ash going into it. Saying that, we would still consider adding something like blood and bone (strong nitrogen content) to ensure it’s neutralised and perhaps even some pine needles (high acidic ingredient).
Step 2: Vigorously massage the ash into the top layer of the sawdust. With time, rain and gravity the ash will settle deeply into the path, you also could water it in if it’s particularly dry in your area to accelerate this integration process.
Step 3: Level it out with your rake and feet so it’s easy to walk along again.
We also added a small amount into our deep litter chicken run which is another form of slow composting in action in our garden. We only put a small amount of ash in as chicken poo’s pH ranges from 6.5 – 8, 8 being fairly high on the alkaline chart so we don’t want to push it over the edge. But, in moderation we’re comfortable to add ash every now and then as a lot of plant waste and other other organic matter is being mixed in at the same time.
- Do a basic pH soil test on your garden so you know whether it’s leaning towards being alkaline or acidic,
- If you’re using wood ash on your vegie beds or orchards (and don’t have acidic soils), use it very sparingly,
- Add small amounts into your compost pile/bin every now and then, and
- As a way of processing ash in bulk, consider adding it into in situ slow composting systems like the swale path or deep litter chicken run. Where required add in other ingredients which can help neutralise (blood and bone) or acidify the contents (pine needles).
The reason we’re so hell bent on keeping ash out of the conventional waste stream is because we’re big fans of nutrient cycling. We’ll do anything we can to keep nutrients onsite as opposed to sending them ‘out there’ where more often than not they transform into pollution. And also, it’s kind of fun to see how much you can really ‘close the loop’ in an urban environment – which is quite a lot!
*Your blogger is Hannah Moloney, co-director of Good Life Permaculture and lover of all things fun and garden-esk.