Does Fire Ash Help The Garden?

F our layers, woolly socks and insulated boots, and a blanket for later. Who would have thought we'd be celebrating the garden in winter like this, night after night? The air is sweet with the smell of rotting apples and damp earth, and here we are around the fire pit again.

In these fraught and isolating times, sitting around an open fire outside, letting the flames ignite our imaginations, feels important; we can get away from screens and reconnect with something ancient. Again, the garden offers a sanctuary, one I am well aware is a luxury that isn't available to all. I do not take it for granted – nor waste its offerings: by the end of the night I have a good layer of ash that, once cooled, I sweep up and save in a bucket. This wood ash is a source of potash or potassium and is an invaluable fertiliser for the garden.

Strawberry plant sprinkled with wood as — Plants use a lot of potassium. Photograph: Alamy

The term potash is literal – pot and ash – derived from the Dutch potaschen. It refers to the process of soaking wood ash in iron pots to dissolve the potassium salts and then evaporate them. Up until the 19th century, this form of potash was hugely important, and used in glass, ceramic and soap-making, as well as fertiliser.

Potassium is a macronutrient, meaning plants use a lot of it during their growing cycle. It is involved in many processes, from photosynthesis to aiding the correct uptake of water and nutrients. It is vital that you burn only organic matter such as logs and newspaper; coal and plastic will poison your soil. As the potassium is water-soluble, it's quickly leached out by rain, so once the fire has cooled, collect and store the wood ash.

Cabbages sprinkled with ashes. Photograph: Getty Images

This can be used in several places. If you have onions and garlic coming up, then a thin dusting between the plants is ideal. Cultivated alliums are hungry things, and they will do well for this addition, as will cabbages and lettuces. Otherwise, store the ash for spring, where it has value for apples, currants, gooseberries and the like. Spread it around their bases and the rain will do the rest. There is little point spreading it over bare ground as with no plants to sup it up, it will just wash away.

If you don't have the space to store the wood ash, add it to your compost pile, which can absorb no end of the stuff. Being an alkali, it will sweeten the contents of the bin that naturally errs on the acid side.