Gardens: The Surprising Benefits of Acid Rain

Showing the ecological devastation that sulphuric acid raining down from the sky had on forests and waterways across the world. Yet the decline over the past 30 years in the emissions of toxic sulphur dioxide in air pollution that once caused this phenomenon has had an enduring impact on British soils, with far-reaching effects on agriculture and even our gardens — and not always a positive one.

Sulphur is a key plant nutrient vital to healthy growth, but UK soils are naturally deficient in this essential mineral. Back in the 1980s this was of little concern to growers as these levels were continually topped up by “atmospheric deposition”, ie acid rain.

Fast forward to 2016 and this is increasingly worthy of attention. One small survey conducted over 2014 and 2015, for example, found that only 13% of the crops sampled showed sulphur levels in the “normal” range, with the rest registering as low or slightly low. This is a concern as inadequate sulphur levels have been shown to slash farm yields of some (but admittedly not all) crops by as much as 50%. Surprising as it may seem, even acid rain clouds can have a silver lining.

As many plants also use sulphur pulled up from the soil to generate defence compounds to help ward off pests and diseases, this deficiency can also result in weak, vulnerable crops that require higher pesticide applications. These defence compounds also happen to be the exact same chemicals that give vegetables, like onions, garlic, broccoli and sprouts, their characteristic flavour and associated health benefits. Heard about the antioxidants in broccoli and garlic? It’s the sulphur chemicals, derived from the soil, that are doing the work.

While this effect is likely to be greater in agricultural soils, where crops are constantly taking sulphur from the soil only to be harvested and removed from the site, this can be an issue even in garden soils. Take lawns for example: years of continual mowing and disposal of the grass clippings essentially mimics that of agriculture – acting like a pump on a conveyor belt to suck up the sulphur.

If you suspect your soil is sulphur-deficient, there is a simple solution that offers all of the benefits without the damaging acidity: Epsom salts. This naturally occurring mineral combines both sulphur and another essential plant nutrient, magnesium, in a double whammy and can be bought for minimal cost at any garden centre. Simply sprinkle over the ground according to package directions for higher yields of tastier and more nutritious crops.