Ancient Soil Amendments: Ash

This is the sixth in a series of blogs, about ancient soil amendments used in the garden. Each blog will discuss a common and specific type of soil amendment used in the garden, along with documentation for its use, as well as occasionally discussing why a particular soil amendment was chosen, or its relation to modern gardening practices. The original blogs, along with other gardening related blogs, can be found here.

There is a time and place for ash in the garden. High in lime and potassium (and containing carbon, calcium, and magnesium), if you burn wood you automatically generate it for free and without the work necessary to obtain other fertilizers. Free fertilizer and soil building is always nice.

Apples in particular apparently like ash, but young plants might burn if it is placed on their tender leaves. Slugs and snails are reluctant to cross dry ashes, but overall ash is considered very alkline so most garden reference materials say to use it carefully.

Varro talks about using ash – specifically in areas where there is no
natural “salt”, and how the locals in these places instead added “salty coals” obtained from “certain kinds of woods.” Interestingly, what type of
wood you burn makes a difference when determining the fertilizer value, so the reference Varro makes to “certain kinds of woods” is not just ancient fortunetelling.  Columella says that good farmers should use ashes when creating “manure” for the garden.

Beyond as a soil amendment, there are a variety of other ways ash was used in the garden. Ibn al-‘Awwām said to use ashes of fig or oak to help yellowing trees (Crop Protection in Medieval Agriculture, p114, J. Zadoks, 2013). Ashes were spread alone or added to mixtures which were then spread on plants (from trees to young vegetables) as a way to stop all manner of insects, and spread over young plants to help protect them from night frost.

Pliny suggests ashes are a more gentle salt, and useful for keeping figs and rue from rotting at the roots and an early 17th century author suggests using ash from holm oak as a way to get rid of voles (Zadoks, 2013). In the Geoponika, Didymos says ashes “are the best” because it also kills fleas and borer beetles beyond its natural benefits to the soil (p248). In fact, there are 20 references to the ways a farmer can use ashes in Geoponika.

Clearly, ashes were a pretty common addition to the garden, especially since many of the plants that don’t particularly like them (potatoes and blueberries, for example) are New World plants. If you want a quick way to garden like a medieval gardener – ashes are an easy way to get started!