What is mycorrhizal fungi and why do I need it in my garden?

No doubt you’ve heard the term ‘mycorrhizal fungi’, but do you know why you need it in your garden? Especially during autumn, winter and early spring when you might be considering doing some bare root planting.

These clever fungi have been around for a while. Maybe about 500 million years, in fact. They actually enable roots of plants, particularly important for trees and shrubs, to be more effective.  They do this by means of tiny threads called hyphae. The word mycorrhiza actually means ‘fungus root’. They allow the roots of a plant to achieve a greater network underground, therefore greatly enhancing the search for food, trace elements and water. Mycorrhiza basically extend the range of the roots, reaching out with spidery arms in order to collect useful nutrients, which are fed back to the plant. They are exceptionally efficient at sourcing phosphorus from the soil and highly effective at absorbing water.

The fungi, pictured above, are present in most soils to a greater or lesser extent. They thrive in soil that is relatively undisturbed and there are far fewer in soils that are regularly dug. The symbiotic partnership provided by mycorrhiza benefits both parties. The plant provides sugars and carbon for the fungi, in return for nutrients and water. Studies have shown that the very earliest plants known to man appear to show its presence and the organism was around before the dinosaurs. We can also benefit from the delights that this fungus provides in the form of edible mushrooms and, in particular, truffles!

There are many different types of mycorrhizal fungi and just one tree might show the presence of up to 15 types. In a small wood there could be around 8000 different species of the fungi, all linking underground. Smaller, softer plants have a different type of mycorrhizal fungi which are hosted in the actual plant root rather than in the soil. Vegetables and fruit such as tomatoes, strawberries and broad beans all use this beneficial network. Brassicas, however, don’t generally use mycorrhizal fungi and ground that has been regularly used for brassica growing contains very little. Chemically fertilised soil also doesn’t contain many mycorrhiza and any fungicide will kill them.

Do you need them in your garden?

The answer is ‘yes’. But many gardens will contain them already. You can enhance and spread what’s there already by applying mulch and gardening organically. If you have inherited a patch that was recently a building site, or has been over-worked, there will be very little in terms of beneficial fungi. So it would be a great idea to regularly include them whenever you do any planting. If, however, your soil has been recently treated with chemicals, your mycorrhizal fungi will be killed off almost immediately so you’ll need to wait for at least a few months.

What does it mean for your plants?

A healthy and happy plant will establish its root system before putting on too much top growth. it will therefore develop a stable base which is effective at gathering food and water, before concentrating its energies on growing outwards or upwards. If you plant something new and immediately give it a dose of fertiliser, it will start to grow above ground before its roots are really ready to do so.

The result that you might achieve is lots of growth at the expense of longevity. Your plant might also suffer from repeated attacks from aphids and garden pests because it has plenty of soft, new growth to tempt them. The longer-term prognosis for plants that are growing in this un-natural way is far gloomier than those that are allowed to establish at a more natural pace.

The moral of the tale is that patience is a virtue! Allow nature to do its ‘thing’. Give it a helping hand if you can. Avoid chemicals and look for a longer-term outlook.  

The exception to the rule

There is always one! It's annual plants in pots and containers.

You want them to put on a flower or foliage show immediately. There’s a certain amount of nutrient within shop-bought compost but you will need to top it up with fertiliser if you want a prolonged visual feast.