Image above reproduced by kind permission Shigo and Trees, Associates LLC
Mycorrhizal inoculation is a technique of deliberately introducing beneficial soil fungi directly to the roots and to the surrounding soil when planting trees, woodlands or native hedges.
Improves transplant survival rates
Accelerates tree growth rates
Increases tree growth in poor soils
Reduces need for fertiliser and fungicide
Increases resistance of trees to stress and disease
Arrests decline for trees suffering from compaction, salt, drought
The roots of all trees have a symbiotic relationship with a particular class of fungus. This relationship is called a Mycorrhizal association, it is a mutually beneficial relationship where the fungus 'links-in' with the root.
The tree gives up some of its carbohydrates (sugars) which is it has made by photosynthesis to the fungus.
The tree in return gains the use of the extremely large surface area which is provided by the network of fungal strands that penetrate the soil structure.
This enables it to absorb water and inorganic mineral nutrients from the soil. The mycorrhizal fungus coating the root also provide a protection against external disease causing pathogens.
See Mycorrhizae - The Biology for a more in-depth explanation.
We at Eco Tree Care & Conservation Ltd have planned and planted large scale tree planting projects where we have worked side by side with soil scientists and horticultural experts.
This has given us a broad network of expertise and access to the highest quality mycorrhizal products currently available on the market.
This expertise is essential as there are many products out there that are so general in there mycorrhizal content that they are not necessarily the correct choice for tree and woodland planting.
Our planting experience & knowledge of mycorrhizal innoculation gives the best possible start to newly planted trees.
Native hedge planting in North London -
Mycorrhizal inoculation is standard on all
our tree & woodland planting schemes.
Trees in a heeling-in bed prior to woodland planting
These trees have been inoculated prior to heeling in.
They will be re-inoculated at the time of planting.
In the early days of forestry
research into woodland planting & tree survival,
inoculation of young trees with mycorrhizal fungi
of the Ectomycorrhizal type (EM) (see
Mycorrhizal Inoculation - The Biology) involved
macerating and liquidizing the roots of ‘donor’
trees.The seedling root was dipped into the slurry
prior to planting. The planting survival results
were inconsistent and the preparation also did not
have long shelf life.
It was only in the 1980s that EM mycorrhizal fungi were finally cultured on a commercial scale and induced to form spores. One of the first to offer a viable mycorrhizal inoculant for woodland planting was a company called ‘Plant Health Care’ in the USA. The inoculant was based on the species Pisolithus tinctorius, found on more than 100 species of woodland trees and shrubs worldwide. Trials by the company produced increased tree growth rates of up to 200 percent in the seedlings of several pine tree species.
Mycorrhizal fungi are not found in subsoil and dislike disturbed ground, so it is common to find that they are absent from gardens of new-build houses or where there has been recent landscaping. Inoculation of the roots of newly planted tree seedlings can dramatically increase the success of new plantings in such situations. Simply digging over beds or hoeing in a garden can disrupt existing mycorrhizal relationships, so there is certainly no harm is introducing mycorrhiza with the planting of trees and shrubs either singly or as part of a larger hedge or woodland planting project.
A cycle of negative feedbacks is common in gardens: disturbance damages the fungal partners of plants, making them less able to absorb nutrients, so the gardener adds a chemical ‘fix’ of inorganic fertiliser, which is toxic to the fungi, making them even less able to supply the plant. The cycle is self propelling.
This is the situation that modern farming now finds itself in, the living soil system has been killed with chemical fertilisers, pesticides, insecticides, fungicides and so on. The cycle is only being slowly broken by adoption of organic farming practice.
Mycorrhizal fungi form
associations with fine, actively growing fibrous
roots, so the fungus need to be physically introduced
to this part of the tree. For new plantings the
simplest method, now well-established in forestry
and landscaping, is to apply a solution containing
the inoculant by dipping the roots in a liquid or
gel formulation (see below).
This technique is only really suitable for dormant, bare-root trees which are only available between November and early April.
gel-based root-dip formulation containing
in the planting of new woodlands
These Grafted Walnut trees have just been dipped into an mycorrhizal inoculant solution prior to planting
Bare-root tree planting during the winter planting season is greatly aided by Mycorrhizal Inoculation
For pot-grown trees, tablets or powdered formulations can be mixed into the growing medium. The nursery industry has been quite slow to take up this method, probably because plants grown in sterile media and supplied with all their water and nutrient needs may show little extra growth after inoculation.
While large growth increases have been found in some cases, results have been mixed. Generally, though, inoculated plants trees never perform worse than those that have been left untreated.
Once they are planted if they have a mycorrhizal association then they are more likely to survive and thrive.
Treated, pot-grown stock, when planted out and exposed to soil pathogens for the first time, have been shown to establish more quickly with better disease-resistance, and thus suffer less from ‘transplant shock’.
Well-established plants including mature trees can also be inoculated.
On a small back-garden scale
this can be carried out simply by ‘pricking’
the soil with a fork all around the rooting zone
of a tree and introducing the mycorrhiza by spraying
the area with a liquid solution of mycorrhizae using
a knapsack sprayer.
A more industrial technique employed is ‘Terravention’ which physically blasts fungal inoculants into the root system using pressurised nitrogen gas, and is particularly valuable in areas that are suffering from soil compaction, as the gas opens up air channels to some depth, such as in sites where there is a lot of pedestrian or vehicular traffic and on building sites.
The Royal Botanic Gardens, Kew reversed the seemingly-terminal decline of several specimens, including some of its oldest trees, with Terravention. A Platanus orientalis planted in the original garden in 1761 and a Sophora japonica from 1762 were both re-invigorated by Terravention in 1997, and a Cedrus deodara, marked for removal since two-thirds of its crown was completely defoliated, greened-up within months of treatment. All three continue to recover well.
New Woodland, Orchard &
Native Hedge Planting
During our 2007 to 2011 tree planting seasons we used preparations of the following fungi as our Mycorrhizal Inoculant in our new woodland, orchard and native hedge planting projects.
Endo Mycorrhizal species
- Glomus clarum, G. intraradices, G. mosseae, G.
deserticola, G. monosporus, G brasilianum, Gigaspora
Ecto Mycorrhizal species - Pisolithus tinctorius, Rhizopogon sp. Biofixed beneficial soil bacteria and fungi, Biofixed beneficial soil bacteria and fungi, (Bacillus spp., Pseudomonas spp., Arthrobacter sp., Acetobacter sp., Lactobacillus sp., Lactococcus sp., Comamonas sp., Nitrosomonas sp., Nitrobacter sp., Rhizopus sp., Phanerochaete sp., Saccharomyces sp., Sporotrichum sp.