Agricultural lime or elemental sulphur are recommended to modify soil pH to a range that suits healthy growth of particular plants. A reader recently asked me if “Lime Sulphur” was suitable to use around roses in her organic garden.
‘Lime Sulphur’ or ‘Lime Sulfur’ is a fungicide/pesticide formed from reacting calcium hydroxide (made from adding water to quicklime) with sulphur. It is usually applied when roses are dormant as it can burn foliage.
Hydrated lime is very reactive and should not be used where plants are growing. Lime Sulphur solution is quite alkaline (pH 10.5–11.5) and corrosive. Gloves, goggles, face masks and protective clothing must be worn as the pesticide is very irritating to the eyes, skin and respiratory passages. See the Material Safety Data Sheet for this product.
Plants are affected by diseases when they cannot get enough of the elements (including sulphur) they need for a healthy immune system either from inadequate fertiliser, or an unsuitable soil pH (because pH controls the availability of different nutrients to plants), or soil that is either too dry for the roots to absorb the nutrients, or is waterlogged and very acidic.
Although some sources state that Lime Sulphur fulfils requirements of organic gardening groups, the ‘Australian Certified Organic Standard 2010‘ lists Lime Sulphur as a restricted product and notes that it has a potential impact on beneficial insects.
My advice is to maintain a moderate amount of well-made compost in your topsoil, where compost holds all nutrients (including sulphur) close to plant roots; adjust irrigation and soil pH, and provide suitable amounts of complete organic fertiliser. In the meantime, if your plants have a serious fungal problem, I suggest you use Organic Crop Protectants’ organic-registered ‘Eco-fungicide’. It won’t damage your plants or your soil, and it is kind to beneficial insects.