By Victoria Torley

Why is it that some plants thrive and others, not so far away and supposedly in the same soil, do poorly? Is it just fertilizer? Compost? A secret ingredient?

Okay, it’s "a secret" ingredient. Actually, it doesn’t have a single name, it’s a relationship.

The Mycrorrhizal Relationship. Romantic, isn’t it?

When I first heard of ‘mycorrhiza,’ I thought it sounded like one thing. It isn’t, it is a whole bunch of things, all of them tiny little fungi classed in two groups, ectomycorrhizae and endomycorrhizae.

You can immediately forget ectomycorrhizae (unless you are growing trees like birch, spruce, and oak) and simply concentrate on endomycorrhizae (which is a good thing because who wants to memorize two long names), which are important for almost everything that isn’t a birch, spruce or oak.

Here’s the important part: endomycorrhizae form a relationship with the roots of plants to help them absorb nutrients.

This is vital for the plants because roots can only absorb nutrients if they are in direct contact with the soil. You don’t need a microscope to see roots. Their limited surface area means that they have a limited amount of contact with the soil.

Enter mycorrhiza, which are microscopic and can, in essence, multiply the soil contact of the root by ten or more. More contact, more nutrients. More nutrients, healthier plant. If all that wasn’t enough, mycorrhiza can help protect the plant from trouble.

What kind of trouble? Some mycorrhizas excrete enzymes that are toxic to nematodes. Others act as a kind of primary immune response, kicking the plant’s system into defensive mode.

Other mycorrhizas excrete organic acids that dissolve ions and allow them to be used by the plant. In poor soils, mycorrhizae allow plants to take up more of the available nutrients. In a world where the uptake of CO2 is increasingly important, adding mycorrhizae to poor soils also takes on a new importance.

Mycorrhizae are a great help to plants, but what do the mycorrhiza get out of it? They get sugar. As the plant produces sugars for its own growth, it sends the excess sugars to the fungi, enabling them to grow.

When they are ready, the fungi send a ‘fruiting body’ up to the surface as a mushroom. Just one more thing to like about mycorrhizae.

Now, in case you are wondering, you can buy packaged mycorrhizae and add them to your soil. There are a number of different suppliers available by typing in ‘mycorrhizae.’

Plant for the week.  There is one plant that could not exist if it weren’t for specialized mycorrhizae called orchid mycorrhizae. All orchids are myco-heterotrophic at some point, usually at the start of life.

Orchid seeds are too small to take in the carbon they need to grow and must fall on moss, bark or soil that contains mycorrhizae to survive. Some orchids outgrow their need for the relationship and some are dependent on it life-long.

This lovely orchid is the Guarianthe skinneri and it is the national flower of Costa Rica.

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Find more interesting stories about gardening in Costa Rica on the AM Costa Rica Garden Magazine. Questions on this article, Ms. Torley, gardener columnist, can be reached by emailing victoriatorley1@gmail.com
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