Q What are mycorrhizal fungi?
A Mycorrhizal fungi form a symbiotic bond with plant roots, which means that both the plant and the fungi benefit from the relationship. The fungi live in the soil and grow onto and into a plant’s roots, quickly forming a root-like network that effectively expands the plant’s roots into a wider area of soil, allowing it to take up water and nutrients more easily.
Some nutrients, especially phosphorus, don’t move around in the soil with the natural flow of water, so it can often be difficult for a plant to access them. The mycorrhizal fungi take up these nutrients and transport them directly to the plant. In return, the mycorrhizal fungi receive carbohydrates from the plant.
Understanding of mycorrhizal fungi is currently limited, but soil scientists are now starting to uncover their beneficial role in soil and plant health, as well as their enormous variety.
Caption: Mycorrhizal fungi can be bought at the garden centre
Q Where are mycorrhizal fungi found?
A Mycorrhizal fungi are present in almost all soils in greater or lesser amounts. They vary according to the soil type and location, so those that are present in a clay soil in Scotland may not be present in a sandy soil in the south of England. Many species are thought to be specialists, only associating with specific plant species, while others seem to interact with a wide variety of plants.
Your garden soil should contain a good mix of mycorrhizal fungi, although it’s thought that applying inorganic fertilisers, such as Toprose, might impede the natural lifecycle of the fungi, possibly as plants don’t need their help to take up nutrients.
Q What is a mycorrhizal fungi treatment?
A You can find a variety of mycorrhizal fungi treatments in most garden centres. They are usually sold in plastic resealable sachets that are filled with the fungi in the form of powdery granules. This substance is made up of the fungi themselves, mixed with an inert clay carrier to keep them alive and also help distribute them in the soil.
There’s generally a mix of mycorrhizal fungi species in each pack. However, there’s no guarantee that they will be the best ones for your soil, or that your soil will not already contain these species.
Some critics also question whether the fungi will still be alive by the time they’re applied to the soil. A few of these products also contain some plant nutrients. We sent samples for testing, to see which ones did contain these and at what ratio. Some also claim to contain biostimulants, but we have no way to verify this.
Manufacturers of these products also suggest using them when planting trees, shrubs and perennials, as well as on vegetables and lawns. They won’t work with brassicas or orchids, which associate with other kinds of mycorrhizal fungi.
Q How should mycorrhizal fungi treatments be applied?
A The treatments all come as powdery granules and some packets contain a spoon to measure out the correct dose. Apply them close to the roots at planting time. Dig a hole, pop in a bare-root plant and shake the right amount over the roots. Tease out the rootball of a potted plant for good contact with the fungi, then back-fill the hole.
Most treatments say that a single application when planting is enough.
Caption: Mycorrhizal fungi treatments should be applied at planting time
Q Are mycorrhizal fungi treatments worth using?
A Most soils contain varying amounts and species of mycorrhizal fungi, and soils themselves are very different around the country, so it wasn’t surprising to see that some treatments gave better results in certain gardens than in others. In some soils, the treatments seemed to give the roses a boost, but this wasn’t uniform across all five gardens.
When we averaged the scores across the five gardens, the roses given the mycorrhizal fungi treatments were largely on a par with those fed with Toprose. This is very positive for those who prefer to garden organically.
Nevertheless, we saw good results in most of our gardens when adding neither a mycorrhizal fungi treatment nor any fertiliser. The gardens in the Cotswolds and Northumberland gave the best results for the control plants. Both are heavier, clay-based soils and have been regularly mulched with organic matter over many years, creating a rich and nutritious soil.
As there is no way of knowing whether any or all of these products will provide the missing mycorrhizal fungi that your soil needs, we feel we can’t recommend any one mycorrhizal fungi treatment over another. They won’t do any harm, but it may not add to what is already in the soil.
If you have had trouble establishing roses in the past, it might be worth trying, but building up your soil’s fertility and health naturally, by adding plenty of organic matter, might be as effective.