Life

Casual Gardener: Mycorrhiza – magic or myth?

Does mycorrhizal fungi 'supercharge' your plants' roots or is it just snake oil?

Mycorrhizal fungi is added to a plant's roots in powdered form
Mycorrhizal fungi is added to a plant's roots in powdered form Mycorrhizal fungi is added to a plant's roots in powdered form

GARDENING is big business – even when you disregard all the 'lifestyle' nonsense. Beyond the essential seeds, plants and tools, there are countless products that promise to boost growth, tackle pests and and even add flavour to your edibles. The marketing of such merchandise isn't solely aimed at those who still rely on chemical solutions, though it's the big agrochemical companies whose products by far occupy most shelf space at the garden centre. Even organic gardeners, typically the most resourceful and thrifty cohort, are encouraged to splash out on items that promise to give them an advantage. Nematodes, seaweed liquid feed and fruit tree grease are just some of the eco-friendly products that aim to make the good life easier.

Another such item is mycorrhiza (pronounced 'my-ko-RYE-za'), which is subterranean fungi that works in partnership with plants and "supercharges" their root systems. The fungi in white powder form are widely available commercially – retailing between £15-20 a kilo – and are sold on the basis that they help plants become more vigorous, overcome health problems and cope better with drought conditions. Marketed as entirely natural, the fungi attach themselves to the plant's root system and grow out rapidly into the soil, searching for nutrients and water. "They essentially become part of the plant's own root system," says one seller, who also claims mycorrhiza can increase the active root area of plants by up to 700 times.

The fungi previously got a brief mention from Gardeners' World presenter Monty Don, who recommended adding it when planting trees, while recent research from the Royal Horticultural Society (RHS), Vitacress Herbs and Royal Holloway University of London showed that the addition of mycorrhizal to soil leads to increased production of essential oils in rosemary, making the plants more aromatic and flavoursome. Mycorrhiza increases the area from which plants can absorb nutrients and water, the study found. Notably, adding mycorrhizal fungi did not affect the shape or structure of the plant, just the production of the compounds that enhance the flavour and taste of rosemary.

The RHS endorses Empathy by Plantworks, a line of mycorrhiza products that claim to be a "viable alternative to chemicals". Tailored for different plant types, the products include RHS rootgrow™, RHS Empathy Supreme Green Lawn Seed, Empathy After Plant Rose Food and Empathy Bulb starter. There's even one specifically for houseplants.

Subterranean mycorrhiza in soil
Subterranean mycorrhiza in soil Subterranean mycorrhiza in soil

However, there's a significant number who think mycorrhizal products are little more than snake oil – the science is surprisingly extensive but conclusions vary. While it's acknowledged that healthy mycorrhizal populations in thriving ecosystems and productive soils are important, their impact as a supplementary growth stimulant is a matter of much debate. The doubters argue that plant roots already have fungal partners in nature, living on the roots, helping plants in exchange for some sugars. They concede that adding mycorrhizal fungi to plants growing in sterile potting media may be helpful, but maintain that a healthy soil should have a good population of these fungi and doesn’t need additional inoculating. By the same token, an unhealthy soil, lacking in organic matter, won’t support mycorrhizal fungi even if they're introduced. Moreover, most plants require specific species of fungi and the packaged product may not contain the right ones. Better, it's said, to make your soil amenable to native mycorrhizae by adding organic matter – ideally include leafmould – and eliminating the use of chemicals, saving yourself money in the process.