The Truth About Mycorrhizal Fungi

Added: 2026-05-07

[00:00:00]Every year, I get asked about mycorrhizal fungi. Should I use it? Is it worth the [music] money? Does it actually do anything?

[00:00:07]I always give half an answer because the full answer takes more than 30 seconds.

[00:00:10]So, today we're doing the full answer.

[00:00:13]Right, mycorrhiza. The word comes from Greek. Myco meaning fungus, rhiza meaning root. Fungus root. That should tell you everything. It's a fungus that lives in and around your plant's roots.

[00:00:25]Over 90% of plant species on Earth form these associations. This is how plants have been growing for 400 million years.

[00:00:32]We're the newcomers with our fertilizers and grow tents. The fungi were here first. Here's what happens underground.

[00:00:38]The type we care about is called arbuscular mycorrhizal fungi or AMF.

[00:00:43]These are endomycorrhizal, meaning they grow inside the root cells. They push through the cell wall and form branch structures called arbuscules.

[00:00:52]Think of them as tiny exchange points.

[00:00:54]At each one, a trade is happening. The plant sends sugars, carbon it produced through photosynthesis, down to the fungus. In return, the fungus sends back phosphorus, zinc, copper, and water.

[00:01:06]The fungal hyphae, these incredibly fine threads, spread 10 cm or more into the surrounding soil. The plant gets access to nutrient pools its roots would never physically reach.

[00:01:18]The fungus gets fed and both sides benefit. So, does it actually matter for chilies? Or is this one of those things that sound great in theory but doesn't show up when you look at the numbers?

[00:01:28]There's decent research on this. A field study published in 2023 from an organic farm in Kansas tested AMF inoculation on five chili pepper varieties over a full growing season. Inoculated plants produced 2 to 8% more biomass with an average 3.7% improvement at final harvest. 3.7% doesn't sound like much, but over hundreds of plants, it does add up. And some varieties responded better than others. Shishito and Islander Bell responded well. Mammoth jalapeno barely budged, so there is a genetic component as well. But here's the finding that really caught my attention. A 3-year study from Poland on sweet peppers found that when you inoculate plants during seedling production, you can reduce your mineral fertilizer by 50 to 75% with no statistically significant decrease in yield or fruit quality.

[00:02:14]I'll say that again. Cut your fertilizer by half to 3/4 with no loss. The fungi made up the difference.

[00:02:21]That's from Capsicum annuum grown in an unheated greenhouse in central eastern Poland. 3 years of data published in MDPI Agriculture in 2023. There's also research showing improved drought tolerance. The fungal hyphae help the plant absorb and retain water more efficiently. If you've ever come back from a weekend away and find your plants wilting, a well-established mycorrhizal network could be the difference between recovery and loss.

[00:02:46]Right, the science is solid. The fungi help. Now, the question that actually matters to me and probably most of you is, is it worth using in pots? Because that's how I grow the majority of my plants.

[00:02:58]The honest answer is it's harder for the fungi to do their thing in pots, and I'll explain why. But that doesn't mean it's not worth doing. Three things work against you in pots. First, temperature.

[00:03:08]Pot walls heat up and cool down much faster than ground soil. Mycorrhizal spores germinate best between 18 and 25° C, and on a hot day in the greenhouse, a dark pot can push well above that.

[00:03:21]The fungi go dormant or die back.

[00:03:23]Second, feeding. If you're using synthetic fertilizers regularly, especially anything high in phosphorus, you're suppressing the fungi. Their whole purpose is nutrient delivery. If nutrients already abundant, the plant cuts back on the carbon it sends to the fungus. The relationship weakens. Why would the plant pay for a service it doesn't need?

[00:03:44]Third, time. Colonization isn't instant.

[00:03:48]It takes weeks for a proper network to establish. In a UK growing season, by the time the fungi are fully active, you might already be into peak fruiting. And if you're potting up multiple times, each pot up disrupts the hyphae.

[00:04:01]Now, compare that to raised beds. I have a couple of raised beds in my polytunnel and I inoculate those.

[00:04:06]Done it once, the fungi are still there because the soil isn't disturbed, the temperature is stable, and the network persists year to year.

[00:04:13]That's where mycorrhizal fungi really earn their keep. But I grow 400 to 500 plants and the vast majority are in pots, so I can't just shrug and say, "Well, it works better in the ground." I have to deal with the reality of pot growing. What I found is that the benefit in pots is real but way more modest. And it depends on how you grow.

[00:04:31]If you're feeding heavily with synthetic fertilizers, you're likely suppressing the fungi anyway, and it's a waste of time. If you're growing in a rich organic mix and feed moderately, then there is benefit to be had.

[00:04:43]Either way, the cost is so low, it's hard to argue against using it. A tub lasts ages, and you really don't need a lot of it. One practical tip, apply it directly to the root ball or into the planting hole when you transplant, not onto the surface. I do add it to my compost mix, but that's okay. But ideally, you want it directly on the roots. The spores need physical contact with the roots to colonize, and sprinkling it on top is definitely a waste.

[00:05:09]One warning, check product labels. Some myco mix products contain Trichoderma fungi alongside the mycorrhizal species.

[00:05:19]Trichoderma is useful in other contexts, but it eats other fungi. If your product has 10,000 Trichoderma spores per gram and 100 mycorrhizal spores, the Trichoderma is going to eat the mycorrhizal spores before they've had a chance to actually do anything and colonize your roots. Read the label, know what you're buying. So, mycorrhizal fungi form a symbiotic relationship with your chili plant's roots. The plant provides sugar and the fungi provide phosphorus, water, and other nutrients.

[00:05:43]Research on peppers show yield improvements, reduced fertilizer needs, and better drought tolerance. Raised beds and ground soil, absolutely use it, and that's where it shines. However, in pots, still use it. It's cheap and it won't hurt, but keep synthetic feeds moderate. Apply directly to the roots and understand that the returns are going to be a little bit more modest.

[00:06:03]Right, if you've enjoyed this video, please hit the like button. And if you haven't already, please subscribe. And [music] until the next one, thank you so much for watching and stay spicy.