Historically, plants were regularly supplied with wood ash in an attempt to boost plant growth and health, improve plant safety and defence against attacks from unwanted pests and critters, and to improve the overall quality of the soil.

The addition of wood ash fertiliser would not only compensate for the deficient trace elements in the soil required for plant growth but would also enhance the amount of different minerals available, including potassium, which is one of the fundamental requirements of a plant, especially during the fruiting and flowering stages of its lifecycle.

Wood ash is simply the leftover residue after the wood, leaves, bark or stem of a tree are burnt. Before jumping to the numerous advantages of the application of wood ash fertiliser on the soil, let us understand where we can get this fertiliser from in the first place.

Bags of wood ash fertilisers are widely available across plant nurseries and seeds stores in the country at meagre prices. The larger sized bags are especially useful for those who are managing vast garden spaces or growing food commercially.

Although wood ash fertiliser is easy to make and purchase, some plants do not thrive when this kind of fertiliser is used

Those who have limited space available for gardening, or have opted for kitchen gardening to compensate for their own family’s food requirements, may find these bags to be an unnecessary expense and waste of space. This is because wood ash fertiliser is generally sprinkled over the soil surface, instead of being poured on to or used as a potting mix, like compost and other fertilisers.

For kitchen gardeners and those with limited resources, wood ash can be obtained for free, or at throwaway prices, from the sellers of chickpea, corn and sweet potato, many of whom sell these commodities by heating them on wood. Similarly, many tandoor shops also use wood and discard lots of wood ash at the end of the day. The only precaution to be taken here is to ensure that only wood is being used and not coal.

Although many gardeners apply small amounts of wood ash directly to the soil, a considerable number of gardeners prefer mixing it up with other ingredients, compost or other fertilisers to prepare a complete meal for their growing plants. Usually, compost rich in vegetable matter is chosen, as wood ash helps to reduce its acidity as well.

The selection of the components being added is usually done by assessing the different nutrient deficiencies and required elements at any specific stage of the plant’s growth. The mixing is done because the salts and lye (the alkaline component) present in wood ash are likely to turn against the plant and burn it away, if used in large quantities. This is primarily the reason why small quantities of wood ash fertilisers are usually scattered and sprinkled on the soil surface or applied after mixing with mulch.

Apart from the macro-nutrients, including phosphorus and excessive proportions of potassium, which is the mainstay of any thriving plant, it also accounts for many other micronutrients and trace elements as well, which are equally beneficial for the plant. Wood ash fertiliser also provides lime to the soil. Not only lime does help to control and neutralise the soil acidity, it also provides calcium and magnesium to the soil. Lime also helps to block plant diseases.

When it comes to nutrients, wood ash fertiliser made with softer woods, like pine, is believed to possess fewer nutrients as compared to wood ash fertiliser made with oak and maple, which are categorised as hardwood. It is also believed that hardwood is likely to produce a greater quantity of ash.

Wood ash fertiliser also acts as a silver bullet to the ever troublesome soft-bodied pests, including the much-dreaded snail and slugs. Infestations from both of these can be a nightmare for any gardener. Dried wood ash fertiliser is helpful in eradicating these pests. It loses its effectiveness and eradication capacity if it turns wet. Therefore, if used as a pest control, a handful of dried wood ash should be sprinkled again.

Although there are many benefits of using wood ash fertiliser, it should be noted that many plants dislike this kind of fertiliser. These tend to include the flowers roses and azaleas, fruits including apples, pears and berries (except for strawberries), and vegetables such as corn, brinjal and potatoes, to name a few.

Finally, it is recommended to never sprinkle wood ash fertiliser when it is too windy or when it is raining. It should also be kept away from water bodies and standing water.

Please send your queries and emails to doctree101@hotmail.com. The writer is a physician and a host for the YouTube channel ‘DocTree Gardening’ promoting organic kitchen gardening

Published in Dawn, EOS, December 24th, 2023