Soil, when looked after, works wonders.
In fact, after years of abusing soil with tractors, chemicals and artificial fertilisers, we are only just starting to learn how well it works when treated well.
Much of that wonder comes down to Mycorrhizae Fungi.
- What is mycorrhizal fungi?
- To what extent does Mycorrhizal Fungi benefit plants?
- How can you encourage mycorrhizal fungi?
- Do you need to add mycorrhizal fungi?
- How do you add mycorrhizal fungi?
- Wrapping up
What is mycorrhizal fungi?
Mycorrhizae fungi is a family of fungus that lives in the soil. The name Mycorrhizae comes from the Greek and means fungus and rhizome.
The fungus develops long threads known as hyphae. There’s a lot of it – in fact, in one single gram of soil you can get up to 20 metres of hyphae.
Fungus performs a number of roles in the soil, but Mycorrhizae is particularly important. The fungus forms connections with the majority of plants, penetrating the cell wall of plants.
These relationships are mutualistic i.e. the relationship benefits both the plants and the fungus. In fact, 95% of plants that form these relationships could not survive without them.
The fungus provides the plants with nutrients that the plant struggles to access by itself. The fungus is particularly good at providing plants with phosphorus, but also provides boron, copper, potassium, selenium, sulphur and zinc. Some forms of the fungus also provide nitrogen in a form which is more easily accessed by plants.
In return, the plants provide Mycorrhizae fungi with carbon (in the form of sugars) produced from photosynthesis.
The benefits don’t end there. Research has shown that Mycorrhizae fungi can improve soil structure as well as help plants to withstand disease and increase their resistance to drought (Gosling et al, 2006).
Mycorrhizae fungi also produces Glomalin, which in turns helps improve soil structure. As we’ve seen before, good soil structure helps plants in all sorts of ways.
Both fungus and plants are choosy about their partners. Plants can determine which fungus are good for them and which aren’t, and deliver more nutrients to good fungus. Meanwhile, the fungus can tell how much carbohydrates plants are delivering. For example, if a plant is in shade and can’t deliver as much carbon, the fungus will reduce the amount of nutrients it delivers to that plant.
To what extent does Mycorrhizal Fungi benefit plants?
Martin Crawford, in his book Creating a Forest Garden, argues that plants with Mycorrhizal connections can grow as much as 4-5 times as much as those without them.
Numerous studies, while not finding quite such a dramatic increase, has shown the mycorrhizal fungi can lead to significant improvements in yields.
That said, mycorrhizal fungi does help some plants more than others. Crops such as spinach and sugar beet, for example, do not form associations with mycorrhizal fungi.
How can you encourage mycorrhizal fungi?
The main benefit of compost is not providing nutrients directly to the plant but in improving the soil. By adding compost to the soil, you can feed the Mycorrhizae fungi so that they can feed your plants.
Research backs this up. For example, a Chinese study by Yang et al found that compost, whether added in large or moderate amounts, enhanced the growth of Mycorrhizae fungi.
You can encourage Mycorrhizae fungi by adopting a No-Dig gardening approach. Instead of digging your gardening (or ploughing your field), you simply add a layer of compost each year and plant straight into the top of your soil.
Do you need to add mycorrhizal fungi?
If you have good soil, you shouldn’t need to add mycorrhizal fungi. The fungus occurs naturally in the garden, and you’re probably better off encouraging the natural growth of the fungus than adding spores.
It’s true some studies suggest that adding mycorrhizal fungi can be as effective as adding fertiliser. However, these were conducted by scientists. Different mycorrhizal fungi provide different benefits for different plants, and unless you are willing to do the research, it’s difficult to know which mycorrhizal fungi to add.
There are also some questions marks as to how long mycorrhizal fungi spores can live outside the ground, and how effective it is adding store bought mycorrhizal fungi to your soil.
That said, there may be times when you do need to add it.
If your soil is poor and you are not getting good results, you may want to consider adding mycorrhizal fungi. However, this should be combined with addressing any problems in your soil, so the fungus is able to survive and flourish.
Some plants will not grow without a specific type of mycorrhizal fungi. For example, orchids will not germinate if certain mycorrhizal fungi is not in the soil.
Using sterilised soil
There are times when you can come across sterilised soil. Plants bought from supermarkets may be planted in sterilised soil, while some farms may sterilise soil to get rid of some pests and diseases.
If you have a bought plant, it’s easier to simply quickly transplant into compost (see How to rejuvenate supermarket pot herbs). However, if you are unlucky enough to take over some sterilised ground, you may want to consider adding mycorrhizal fungi.
How do you add mycorrhizal fungi?
Martin Crawford has suggested two ways to add mycorrhizal fungi without buying it commercially.
- Transplant young tree saplings from ground with good mycorrhizal fungi.
- Place soil from ground with good mycorrhizal fungi around seedlings.
Crawford was primarily focussed on trees, but the Rodale Institute have experimented with ways for vegetable farmers to utilise mycorrhizal fungi.
This involves growing a host plant (bahiagras is a good option) in field soil where it will be inoculated with fungus spores. You can find a detailed explanation of the process here.
You can also add bought mycorrhizal fungi by:
- Dipping roots into water enriched with fungus spores
- Places spores in water, and spray it over foot zones
- Dip plant roots into water enriched with spores.
Mycorrhizal fungi is hugely important for both soil and plants. Understanding how it works can help impact how we manage our soil and plants. For example, we may choose to adopt a no-dig method of gardening, and to enrich our soil with compost.
It’s less clear that adding mycorrhizal fungi has a benefit if you already have good garden soil, but there may be times when it will help.