What You Need to Know About Mycorrhizae and Houseplants

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Mycorrhizal fungi is a hot topic in the houseplant world at the moment, because adding it to our houseplants could potentially make them drought, pest, and disease-resistant.

Before you run out and buy some commercial mycorrhizal fungi and add it to your houseplants, there are a few things we need to bear in mind. Research in this area is still in the very early stages, so there’s a lot of things we don’t know.

What is mycorrhizal fungi?

Mycorrhizal fungi is a type of fungi that forms a symbiotic relationship with a plant – like a less aggressive Venom.

I have a very professional and not at all handdrawn diagram of the relationship between mycorrhizal fungi and plants here:

Fungi can absorb nutrients from soil, but they can’t photosynthesise. Plants can photosynthesise AND adsorb nutrients and moisture from the ground.

They form a mutually beneficial relationship whereby the mycelium (like the fungi’s root system) attach to the roots of the plant, effectively extending them.

The plant sends carbohydrates to the fungi and in return uses the mycelium as an extension of its own root system. The hyphae (individual strands of mycelium) are much finer than plant roots, so can absorb more nutrients and water.

How important is mycorrhizal fungi to plants?

Mycologists are still in relatively early stages when it comes to researching the impact mycorrhizal fungi has ha on the evolution of trees.

It’s thought that the mutualism that occurs between mycorrhizae and plants has been going on for 400 million years and was probably a fundamental part of the evolution of aquatic plants into land plants.

It’s though that 80% of plants have mycorrhizal relationships with fungi BUT most of them aren’t fundamental to the existence of the plant. They can help them become more drought tolerant and pest resistent, but if the mycorrhizal fungi isn’t present, the plant can function perfectly well without it.

However, a few plants, such most orchid species, need mycorrhizal fungi to reproduce in the wild, and at various stages of their development. The orchid seeds are too small to germinate on their own – they don’t have the required nutrients – so they rely on orchid mycorrhiza to help them develop.

Humans can germinate orchid seeds in agar, but the level of success is low in comprison to using mycorrhizae.

Different types of mycorrhizal fungi

  • Ectomycorrhiza

Ectomycorrhizae wrap around the roots of the plant but they don’t actually enter the cell walls. About 2% of plant species use ectomycorrhizal fungi, including willow, pine, and roses

truffles are the fruit of an ectomycorrhizal fungi
  • Endomycorrhiza

Endomycorrhizae penetrate the cortical cells of the plant, so the membranes of the plant and the fungue are in direct contact. There are three further types of arbuscular mycorrhiza that are all endomycorrhizae:

  • Arbuscular mycorrhiza – the most common type of mycorrhiza
  • Orchid mycorrhiza – they tend to stick to orchids. Some orchids are actually parasitic, so the mutual relationship…ain’t so mutual
  • Ericoid mycorrhiza – specific to ericales, so heathers

Research into aroids and mycorrhizae is still in its infancy, but mycologists are pretty confident that several aroids, such as some Philodendron and Syngonium species, are aided by arbuscular mycorrhiza.

How does mycorrhizal fungi benefit plants?

The short answer to this is that the fungi acts as a root system, so the root system is bigger. How much bigger depends on the fungi, but the largest organism in the world is a fungus – Armillia ostoyae (it’s pathogenic though, not mycorrhizal). The bit we see, the mushroom, is a fruit and is very much the smallest part of the operation.

Mycorrhzal fungi can forge networks between hundreds of trees, which mycologists very cutely called the wood wide web.

Works as an extension of the root system

  • Mycorrhizae increases the amount of moisture a plant can absorb

Mycorrhizae are a great denfense against dehydration. Not only does the overall root mass of the plant increase when it connected to mycorrhizal fungi, but it can all go deeper into the ground in search of water.

Hyphae are much thinner than plant roots so can penetrate where tree roots can’t.

  • Mycorrhizae increases nutrient uptake

In the same vein, the increased surface area of the hyphae means that they can access and absorb nutrients that the plant’s root can’t.

Mycorrhizae have also been shown to significantly increase the uptake of phospohorus, which the plant needs for cell division, seed formation, and hardiness. It’s now thought that excessive use of phosphorus-containing fertilisers can damage the relationship between plants and mycorrhizal fungi on arable land.

Allows plants to communicate

As cute as ‘wood wide web’ is, it’s actually pretty accurate.

Research has shown trees using their mycorrhzal networks to redistribute nutrients and warn of incoming inclement weather and even swarms of insects.

Can protect against disease and toxins

Research into this is in relatively early stages, but arbuscular mycorrhizae can provide protection to the trees they’re attached to. Research done into protecting crops from pathogenic fungus showed that adding arbuscular mycorrizal fungi dramatically increases the host plant’s ability to defend itself (source).

We’re not 100% how it works, but there are likely a few different things going on at once.

  1. The AMF makes the plant healthier and better able to fight off pathogens
  2. The presence of mycorrhizal fungi means competition over nutrients for the pathogenic fungi
  3. The AMF can warn the plant of the approaching pathogen so it can prepare to defend itself.
deceiver mushroom – used in labs because it can grow vegetatively

Do all plants use mycorrhizal fungi?

80% of plants use mycorrhizal fungi, but there’s always a few that think they’re too go for it:

  • Brassicaceae – they contain anti-fungal compounds. Don’t buy mycorrhizae for your cabbages!
  • crassulaceae – only 40% of species use mycorrhizae
  • orobanchaceae – there’s not a lot of research here, but it seems like parasitic plants are also parasitic towards mycorrhzae. Rude.
  • proteaceae – they have specialled roots that don’t work well with mycorrhizae.

Will mycorrhizal fungi benefit houseplants?

There’s no doubt that mycorrhizal relationaships are extremely important to a lot of plants, and it’s highly likely that many of the tropical plants that we keep as houseplant form mycorrhizal relationships in their natural habitat.

Even if we know that every single one of our houseplants will benefit from mycorrhizal fungi we can’t assume that buying mycorrhizae and adding to our houseplant soil will have the same effect as it does when the plants are growing in the ground.

Many gardeners swear by adding mycorrhizal fungi to their soil, but will it have the same effect in a pot?

At the moment, soil scientists don’t think that adding mycorrhizal fungi to houseplants will result in a relationship forming between the fungi and the roots of our houseplant, and here’s why:

Fly agaric – mycorrhizal with birch

The pot is a contained environment

The mycorrhizal fungi could help the roots to absorb water, but unless the plant is in a significantly bigger pot than the plant needs (which can lead to other issues, like root rot) then this is largely unnecessary.

it’s not like the fungi can spread outside the pot and into the ground to get water. Can it??

Specific mycorrhizal fungi form relationships with specific plants

Mycorrhizal fungi won’t form a relationship with just any plant. Most have evolved alongside their preferred plant and won’t be of any benefit to the ‘wrong’ plant.

The majority of houseplants (the majority of plants full stop) are thought to form relationships with arbuscular mycorrhizal fungi in the wild, which is an endomycorrhizae. 

The fungi penetrates the plant's cells. 

Most commercially available mycorrhizal fungi are ectomycorrhizae, and therefore wont form a relationship with most houseplants.

You might wonder why companies bother producing ectomycorrhizae when 80% of plant species require endomycorrhizae, but ectomycorrhizae is of great use to the forestry industry (beech and pine use ectomycorrhizae).

80% of commercial mycorrhizae in Europe aren’t viable

Mycorrhizal fungi like to live in quite specific conditions – they like warm, dark conditions, nutrient-rich soil, and can be sensitive to systemic pesticides and (surprise, surprise) fungicides.

They don’t really like being shoved in a bag and shunted about the world in a roasting hot van.

As a result, it’s estimated that when you buy a bag of mycorrhizae, about 80% of them will already be dead. But since you can’t really tell by looking, there’s not really a lot you can do about it.

chanterelle – mycorrizal with birch and pine

It can be tough to keep mycorrhizal alive

If you’re reading this article, you’re proabably well aware that keeping tropical plants in non-tropical places isn’t always easy. However, there are things we can do to compensate – so keeping Monstera in full sun is fine in the UK because it’s about as bright as it gets beneath the rainforest canopy. If you keep your plant somewhere that it can thrive (i.e. warm and bright) it will most likely be too hot for your mycorrhizae.

There is research into using mycorrhizal to protect against pests and disease

Dr Sarah Emery is doing research into how mycorrhizal fungi can protect plant like aglaonema from pests such as thrips, but it’s very early days. Plus, it’s one thing proving that mycorrhizal fungi protect against thrips, and quite another expecting any old mycorrhizal fungi to do the job of one that’s evolved to work with that specific plant.

Will mycorrhizal fungi harm houseplants?

No, they probably won’t last long enough in the soil to do anything at all. If you do manage to get a colony of mycorrhizal fungi going in your plant, then you may find that they compete with your plant for nutrients, because the reach of their roots is limited to the pot.

Mushrooms in houseplants are unlikely to harm them, unless you somehow end up with a pathogenic fungus.

Those little yellow houseplant mushrooms that sometimes pop up are sapotrophic, which means they eat decaying matter. They’ve carved out quite a niche in the houseplant industry – if you’re wonering why mushrooms grow in houseplants, I have an article on that.

Are mycorrhizal fungi worth it?

At this stage in the game, probably not. There’s a lot of anecdotal evience out there from people who swear by them, but soil scientists are sceptical about the effects of mycorrhizal fungi on houseplants to say the least.

It’s also worth noting that mycorrhizal fungi aren’t generally tested on houseplants, because if they are to produce results, those results are reliant on the plant being grown in the ground to be assure the mycorrhizal fungi doesn’t perish.

I’m not saying that mycorrhizal fungi never works on houseplants, just that research into the area is extremely limited, verging on non-existent.

Don’t worry I’ll update this article of any new findings come to light, but for now, you’re better off investing something else.

Caroline Cocker

Caroline is the founder and writer (and plant keeper) of Planet Houseplant

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