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Magic Mushrooms

15 October 2008

12:00 AM

15 October 2008

12:00 AM

We can all think of discoveries, which made little impact at their first introduction, but which changed the ways people worked or lived for ever, nevertheless. Charles Babbage’s ‘Analytical Engine’ of 1840 must be the most strikingly impressive example of this. But I think I may have spotted one in the gardening sphere as well, with the recent harnessing of a scientific discovery of 1885. That discovery concerned the role of mycorrhizal fungi in the soil.

When, some five years ago, I first sprinkled some rootgrow (yes, I know, proper names put in the lower case is annoying and unhelpful but it’s not my fault) in a hole in the ground, before planting a tree, I did so in a spirit of mildly sceptical scientific enquiry. I was intrigued by the ingenuity of scientists at a Kentish firm, PlantWorks, who could turn several strains of native mycorrhizal fungi into granules and sell them at a reasonable price, but I was not convinced that these would genuinely make a difference to how quickly my tree established itself in an unfriendly clay soil.

I certainly did not predict the tremendous impact these ‘friendly fungi’ have had on promoting rapid growth in hostile or disturbed soils and on helping to beat that traditional bane of gardeners, rose replant disease. So startling has been rootgrow’s progress, in fact, that, only eight years after its launch, the Royal Horticultural Society has just endorsed it.

When I first came across rootgrow, I knew a little about mycorrhizal fungi, since they have been studied over many years by horticultural scientists, and are in all the textbooks for professional gardeners. I knew that a symbiotic relationship exists between these fungi, with their network of thread-like filaments (hyphae), and plants, whose fine root hairs they colonise or surround. The plant ensures that the fungi get sugars, which they cannot manufacture themselves without chlorophyll and sunlight, while the hyphae exponentially increase the surface area of ‘roots’ for the uptake of water and soluble mineral salts, especially nitrates and phosphates. (It has been computed that there are up to seven kilometres of filament in seven kilograms of soil.) In woodland, this secondary root system forms a kind of root intranet betwen adjacent trees, so that the nutrients are shared throughout the plant community.

In the wild, more than 90 per cent of plant species are associated with these fungi. In this country, there are two types: those which grow outside the root, ‘ectomycorrhizae’ or EM, which can be seen with the naked eye, and those inside, ‘arbuscular mycorrhizae’ or AM, which are microscopic. Trees tend to associate with EM, while other garden plants relate to AM. I knew this already, but what really took me by surprise was that these naturally occurring fungi could be dried into granules without killing them. But so it has proved. There is also now available a gel which can be used as a root dip for bare-root transplants, like hedging. Only the cabbage family, orchids and ericaceous plants do not derive benefit from rootgrow.

The reason why these friendly fungi are so useful is obvious. Builders, landscape contractors and gardeners are good at destroying them when they muck about with soil, in the process known as digging. Once soil has been badly disrupted, it takes between three and five years for these fungi to re-establish themselves. With rootgrow, the process takes between two weeks and a month. And, once done, it stays done. These formulations are not fertilisers, which need to be reapplied, although they act like them, because the fungi draw in so much more nutrient than the plant roots could do on their own account.

Moreover, if you want to help a plant already in the ground, the trick is to plant an herbaceous perennial, with rootgrow, nearby. The mycelium will, in time, spread to the roots of the established plant.

As if this were not enough, these fungi also exude a glycoprotein called glomalin, which helps bind soil particles together and thus aids drought tolerance. And it would seem they also create a buffer against other environmental stresses like transplantation, weather extremes, excessive use of chemical fertilisers and weedkillers and, crucially, diseases. Three large rose growers, including David Austin Roses, endorse this product as ‘completely effective’ against rose replant sickness.

I have seen the benefit that plants have gained in my heavy soil from using rootgrow. However, extremely useful as it is in the garden, this stuff really comes into its own in large-scale landscape projects, such as new housing estates, the embankments of motorways, and forestry. Indeed, in any circumstances where the mycorrhizal relationships have been severed or they have died out from lack of available hosts, or where a reduction in the use of chemical fertilisers and water is seen as important. Which is, frankly, pretty well everywhere.

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