What Are Mycorrhizal Fungi? A Guide for UK Gardeners
Mycorrhizal fungi: which UK plants benefit, and which don't
By Joe, Founder of Dr Forest · May 2026
Most plants in your garden swap food with a soil fungus. Some don't. Knowing the difference is what makes a mycorrhizal inoculant either worth buying or a waste of money on a row of cabbages.
Mycorrhizal fungi form a partnership with the roots of around 80 to 90% of land plant species. The fungus extends thread-like hyphae through the soil, ferrying water, phosphorus and trace minerals back to the plant. The plant pays in sugars from photosynthesis. The arrangement goes back roughly 450 million years, which makes it older than the plants that have actual roots, and for most garden vegetables, fruit, lawns and ornamentals it's how they actually feed themselves.
But not every plant takes part. Brassicas, beets, spinach and ericaceous plants (rhododendrons, blueberries, heathers) either ignore the partnership or use a completely different fungal group. Inoculating those plants with a standard mycorrhizal product does nothing. The full breakdown of who benefits and who doesn't is below.
This guide covers the two types of mycorrhizae you'll meet in UK gardens, the plants that benefit and the plants that don't, what the research actually shows, and the times when buying an inoculant is worth it.
The yes / no list, in two columns
Plants that benefit
Apply at planting
- Tomatoes, peppers, chillies, beans, peas
- Carrots, onions, leeks, garlic, potatoes
- Strawberries and most soft fruit
- Apples, pears, plums, cherries
- Roses, dahlias, most perennials
- Lawns, grasses, oak, birch, beech, pine
Plants that don't
Save the inoculant
- Brassicas: cabbage, kale, broccoli, cauliflower
- Brussels sprouts, mustard, radish, swede
- Beetroot, spinach, chard, sea kale
- Rhododendrons, azaleas, heathers
- Blueberries, cranberries (need ericoid)
- Carnations and a handful of sedges
Worth applying at planting on the first list. Wasted on the second.
What mycorrhizal fungi actually are
"Mycorrhiza" means fungus-root, and that's what the partnership is. The plant grows in soil. The fungus grows in the soil too, but with thread-like hyphae small enough to reach into pores between soil particles that root hairs can't fit into. The fungus draws water and dissolved nutrients out of those pores and ferries them back to the root, in exchange for sugars from photosynthesis.
The plant gets an effective root system several hundred times larger than its actual roots. The fungus gets a steady supply of carbon it can't make for itself. The arrangement is around 450 million years old, which makes it older than vascular plants and one of the oldest co-operative relationships on the planet.
For most garden plants, this partnership is the main way they take in phosphorus, a useful additional channel for nitrogen, and the way they pick up zinc and copper. Strip the fungi out (through repeated tillage, heavy synthetic fertilising, or fungicides) and the plant has to do all that work through root hairs alone, which is much less efficient.
What's actually happening underground
A: host plant. B: soil surface. C: plant root system, the visible architecture. D: hyphal network, fine fungal threads reaching into pores too small for root hairs. E: arbuscule, where nutrient exchange happens (shown ×500 in inset).
Two main groups, plus a specialist
The types you'll meet in UK gardens
Arbuscular mycorrhizal fungi (AMF, or endomycorrhizae)
The workhorse. AMF associate with around 70 to 80% of all plant species, including most things UK gardeners grow: tomatoes, peppers, beans, peas, carrots, onions, potatoes, strawberries, roses, dahlias, lawns. The hyphae enter root cells and form branching structures called arbuscules, which is where the actual nutrient exchange happens. Almost every commercial mycorrhizal product sold in the UK is built around an AMF blend.
Ectomycorrhizal fungi
Form a sheath around roots rather than entering the cells. Common in woody plants: oaks, birches, pines, spruces, beeches, willows. These are the fungi that produce visible mushrooms and truffles in autumn. Most quality UK mycorrhizal inoculants combine endo and ecto strains so they cover the full planting palette of a typical garden, from a tomato bed through to a hedgerow.
Ericoid mycorrhizae
A different fungal group entirely, partnering with the Ericaceae family: rhododendrons, azaleas, blueberries, cranberries, heathers. Standard endo/ecto inoculants do not contain ericoid fungi. If you're planting ericaceous specimens into a new bed, look for an ericoid-specific product or accept that the natural soil population will colonise over time. The two groups don't substitute for each other.
The long list
Which plants benefit
Most UK garden plants take part in the standard endo or ecto partnership. The list is long enough that the question "which plants benefit?" is almost equivalent to "everything except brassicas, beets and ericaceous plants".
Vegetables. Tomatoes, peppers, chillies, beans, peas, carrots, onions, leeks, garlic, potatoes, sweetcorn, courgettes, squash, cucumbers, strawberries.
Fruit. Apples, pears, plums, cherries, raspberries, blackberries, currants, gooseberries.
Flowers. Roses, dahlias, peonies, hardy geraniums, most herbaceous perennials, most annuals.
Lawns and grasses. Nearly all turfgrass species, plus ornamental grasses.
Trees and shrubs. Oak, birch, beech, pine, spruce, willow, hazel, hawthorn, blackthorn. Most native hedging.
If a plant isn't on the don't-benefit list below, assume it benefits.
Where the inoculant does no work
Which plants don't
Three plant groups either don't form mycorrhizal partnerships or use a different fungal group. Standard inoculants do nothing for them.
Brassicaceae. Cabbage, broccoli, kale, Brussels sprouts, cauliflower, mustard, radish, turnip, swede, oilseed rape, rocket, watercress. Brassicas evolved root chemistry that actively excludes mycorrhizal fungi: they release glucosinolates and isothiocyanates (the same compounds that give them their pungent taste) which suppress fungal colonisation. The plant grows fine on its own, but the soil fungal population takes a knock wherever brassicas grow heavily.
Chenopodiaceae. Beetroot, spinach, chard, sea kale. Either don't form the partnership or only weakly.
Ericaceae. Rhododendrons, azaleas, blueberries, cranberries, heathers. These plants partner with ericoid mycorrhizal fungi, a different specialist group. A standard endo/ecto inoculant does nothing for them. Either source ericoid-specific spores or rely on the natural soil population.
A handful of others fall outside the partnership too: carnations, certain sedges, and a scattering of others most gardeners won't run into.
If your bed is mostly brassicas, save the inoculant for somewhere it'll do work. If it's mostly tomatoes, peppers and roses, the partnership is the difference between a plant feeding through ten centimetres of root and a plant feeding through several metres of fungal network.
The reference index
What the research shows
The peer-reviewed numbers
The research base for AMF is substantial and the effect sizes from controlled trials are large. A few representative findings.
The findings are consistent across crop species and growing conditions. The size of the benefit depends on how starved of phosphorus or water the soil is to begin with: a well-fed allotment with healthy biology will see a smaller uplift than a new-build garden of compacted subsoil. Mycorrhizae buffer the plant against the conditions where yields would otherwise drop, and that buffering is what shows up most consistently in the literature.
Application
How to use a mycorrhizal inoculant
The single most important rule: contact. The fungal spores have to physically touch root tissue to start colonising, so applying inoculant powder to the soil surface and watering it in does almost nothing. Two methods that work.
In the planting hole. Pour a teaspoon or so of powder into the hole, set the rootball on top, backfill. Roots growing down through the powder will encounter spores immediately and colonisation starts within days.
Direct to the rootball. Dust the powder onto exposed roots before planting, particularly when potting on or transplanting. Bare-root trees and hedging plants get coated easily and benefit visibly within the first growing season.
For seed sowing, mix a small amount of inoculant into the planting compost so seedling roots meet spores as they emerge.
One application is usually enough for the life of the plant. The fungus colonises and multiplies inside the root system. You don't need to top up annually the way you would with a fertiliser. Inoculate at planting, look after the soil afterwards, and the partnership maintains itself.
Easy to undo
What kills the partnership
A few common practices kill mycorrhizal fungi or suppress the partnership before it gets going.
High-phosphorus fertilisers. When phosphorus is freely available in the soil solution, the plant stops "paying" the fungus and the partnership fizzles. This is why heavy use of synthetic feeds with NPK figures like 10-50-10 reduces mycorrhizal colonisation in glasshouse and field trials. Slow-release organic feeds with moderate phosphorus content (6-10% P range) don't trigger the same effect.
Most fungicides. Designed to kill fungi, generally don't distinguish between pathogens and beneficials. Drench fungicides applied to the root zone are particularly damaging.
Heavy tillage. Disrupts the hyphal network, which can take seasons to rebuild. The argument for no-dig and reduced cultivation is largely an argument for keeping the soil biology intact.
The supportive practices are roughly the same as the practices that build soil biology in general: no-dig or reduced-dig cultivation, mulching, cover cropping, organic matter at the surface, and a light hand with synthetic feeds.
When to apply, when not to bother
Quick reference
Tomatoes, peppers, courgettes
Heavy fruit-set demand for phosphorus and water. Inoculate at planting, in direct contact with the rootball.
Cabbages, kale, broccoli
Brassica root chemistry actively excludes the partnership. Spend the money elsewhere.
New lawn or perennial border
One application at establishment supports the bed for years if soil isn't disturbed afterwards.
Rhododendrons or blueberries
Need ericoid mycorrhizae, a different fungal group. Standard endo/ecto inoculant does nothing.
Container plants in fresh compost
Sterile compost has no native fungal population. Inoculate the rootball before potting up.
Established no-dig bed
Healthy soil biology already carries native populations. Re-inoculation is rarely worth it.
The plant gets an effective root system several hundred times larger than its actual roots. The fungus gets a steady supply of carbon it can't make for itself.The 450-million-year deal
Endo and ecto mycorrhizae in one powder
Multi-strain inoculant covering the standard partnership for tomatoes, peppers, fruit trees, roses, perennials, lawns, hedging and most native trees. Made in Stockport in small batches, plant-based, with no slaughterhouse waste. Apply once at planting, in direct contact with roots.
So, briefly
Mycorrhizal fungi are a real partnership with serious research behind them, but they aren't a universal product. They work for the great majority of garden plants and they don't work at all for brassicas, beets and ericaceous specimens. Apply at planting, in direct contact with roots, into a bed that hasn't been recently fungicide-treated. Avoid high-phosphorus feeds afterwards. One application usually lasts the plant's life. The job is mostly about not killing the partnership once it's started.
Frequently asked
Frequently asked questions
What are mycorrhizal fungi?
Mycorrhizal fungi are soil fungi that form a symbiotic partnership with the roots of around 80 to 90% of land plants. The fungus extends thread-like hyphae into the soil, drawing water, phosphorus and trace minerals into the root in exchange for sugars from photosynthesis. The arrangement is around 450 million years old. For most garden plants, this partnership is the main way they take in phosphorus and a useful additional channel for nitrogen, zinc and copper.
Which plants benefit from mycorrhizal fungi?
Most UK garden plants benefit. Vegetables that benefit include tomatoes, peppers, chillies, beans, peas, carrots, onions, leeks, potatoes, sweetcorn, courgettes, squash and strawberries. Fruit includes apples, pears, plums, cherries and most berries except blueberries and cranberries. Flowers include roses, dahlias, peonies and most herbaceous perennials. Lawns and most trees (oak, birch, beech, pine, willow) also form the partnership. As a rule of thumb, if a plant isn't a brassica, beet or ericaceous specimen, assume it benefits.
Which plants don't benefit from mycorrhizal fungi?
Three groups don't benefit from standard endo/ecto inoculants. Brassicas (cabbage, kale, broccoli, cauliflower, Brussels sprouts, mustard, radish, turnip, swede) actively exclude mycorrhizal fungi through root chemistry. Beets and spinach (Chenopodiaceae) either don't form the partnership or only weakly. Ericaceous plants (rhododendrons, azaleas, blueberries, cranberries, heathers) need a different fungal group called ericoid mycorrhizae. A handful of others, including carnations and certain sedges, also fall outside the partnership.
What's the difference between endomycorrhizae and ectomycorrhizae?
Endomycorrhizae (also called arbuscular mycorrhizal fungi or AMF) enter root cells and form branching structures called arbuscules where nutrient exchange happens. They partner with around 70 to 80% of plant species, including most vegetables, fruit, flowers and grasses. Ectomycorrhizae form a sheath around roots rather than entering the cells, and partner mainly with woody plants like oaks, pines, beeches and willows. Most quality UK inoculants combine both types so they cover the full planting palette of a typical garden.
Are mycorrhizal fungi worth using on tomatoes?
Yes. Tomatoes are one of the strongest beneficiaries of AMF. The partnership improves phosphorus uptake (which tomatoes need heavily for fruit-set), supports drought tolerance, and reduces transplant shock. Apply mycorrhizal powder directly to the rootball or into the planting hole when planting out. One application at planting is usually enough for the life of the plant. Avoid high-phosphorus liquid feeds afterwards, since freely available phosphorus suppresses the partnership.
When should I apply mycorrhizal fungi?
At planting, in direct contact with roots. The fungal spores have to physically touch root tissue to start colonising, so surface applications and watered-in applications do almost nothing. The two methods that work are pouring powder into the planting hole before backfilling, or dusting powder directly onto the rootball before planting. For seeds, mix a small amount of inoculant into the planting compost. One application usually lasts the life of the plant; you don't need to top up the way you would with fertiliser.
How long does one application of mycorrhizal fungi last?
Usually the lifetime of the plant. Once colonisation begins, the fungus multiplies inside the root system and spreads through the surrounding soil. The partnership maintains itself as long as the soil isn't deeply disturbed or treated with fungicides, and the plant isn't fed with high-phosphorus synthetic fertilisers that suppress the partnership. For perennials, trees and lawns, a single application at establishment is normally sufficient. Annual top-ups are unnecessary in healthy soil.
Do mycorrhizal fungi work in pots and containers?
Yes, and inoculation is particularly worthwhile in containers because fresh sterile potting compost has no native fungal population. Apply mycorrhizal powder directly to the rootball before potting up, or mix into the compost as you fill the pot. Avoid high-phosphorus liquid feeds afterwards, which suppress the partnership. The inoculant is most effective in larger containers where the root system has room to develop and benefit from the extended fungal network.
Will high-phosphorus fertilisers kill mycorrhizal fungi?
They don't kill the fungi outright, but they suppress the partnership. When phosphorus is freely available in the soil solution, the plant stops sending sugars to the fungus, and colonisation falls off. Synthetic feeds with NPK figures like 10-50-10 reduce mycorrhizal colonisation in trials. Slow-release organic feeds with moderate phosphorus content (6 to 10% P range) don't trigger the same effect, since the phosphorus isn't released as a soluble pulse but slowly over weeks.
Can I use mycorrhizal fungi with no-dig gardening?
Yes, and the two practices reinforce each other. No-dig avoids disrupting the hyphal network, which is one of the main things that breaks the partnership down. An established no-dig bed often has substantial native mycorrhizal populations after a couple of seasons, so re-inoculation is rarely needed. The case for inoculating is strongest at the start: the first time you plant into a new no-dig bed, especially if the bed was built on imported topsoil or compacted ground that may carry low fungal populations.
The working, shown
- Lu, N. et al. (2023). Effects of arbuscular mycorrhizal fungi on phosphorus uptake in maize. Soil Biology and Biochemistry, study summary.
- Zaman, M. et al. (2024). AMF colonisation and nutrient uptake under drought stress at varying C:N ratios. Plant and Soil.
- Figueiredo, A.F. et al. (2021). Common mycorrhizal networks and seedling establishment. Mycorrhiza.
- Alam, M.K. et al. (2024). AMF biofertilisers and reductions in chemical fertiliser inputs. Agriculture, Ecosystems & Environment.
- Fall, A.F. et al. (2022). Hyphal networks, glomalin, and soil aggregate stability. Soil and Tillage Research.
- Smith, S.E. and Read, D.J. (2008). Mycorrhizal Symbiosis (3rd edition). Academic Press. (Foundational reference for the biology summarised throughout this guide.)
- Brundrett, M.C. and Tedersoo, L. (2018). Evolutionary history of mycorrhizal symbioses and global host plant diversity. New Phytologist, 220(4), 1108–1115.