Are cremated ashes good for plant growth?

Hannah - So, it turns out that burning a body results in ashes that are rich in phosphates, calcium, potassium, and sodium. Could these benefit a plant? I went to visit Sally Petite, Head Gardener at the beautiful Cambridge University Botanic Gardens.

Sally - It's really interesting concept, the idea of adding human ashes to plants to improve growth.

All plants ultimately require a balance of what we call macronutrients which are things like nitrogen and potassium and also, micro-nutrients such as zinc and carbon and manganese. These all exist in plants in a very, very finely tuned balance. An excess of anyone of these individually can have an impact on plant growth.

So, for example, calcium will rapidly reduce the supply of nitrogen within a plant which affects protein and growth and result potentially in a poor yield of plants or fruit. An excess of calcium will also result in a reduction of the water control and photosynthesis and this can be apparent in things like browning, scorching and spotting of leaves.

Again, with an excess of phosphorus, the fruits will mature early and you will actually potentially have a poor yield of crops because the plant hasn't actually established properly to support a very high yield. Similarly, an increase in salts or sodium can increase particularly osmotic pressure or the water pressure within a plant and actually, ultimately result in dehydration.

So, potentially, the addition of human ash to a plant may in fact be a detrimental effect rather than a positive one.

Hannah - Thanks, Sally and it turns out that the nutritional content of ashes can vary between individuals, depending on diet, where you live and age. Plus, if mercury or gold fillings feature, traces of these in the ash could be toxic to the plant.