What Are Mycorrhizal Fungi? A Guide for UK Gardeners

Mycorrhizal fungi form symbiotic relationships with plant roots, improving nutrient and water uptake for most plants. This symbiosis benefits around 80–90% of land plant species and has existed for over 450 million years.

How They Work

The fungi extend thin hyphae into the soil, greatly increasing the root system's effective surface area (often hundreds of times). The plant supplies the fungus with sugars from photosynthesis. In return, the fungus delivers water and nutrients—especially phosphorus, nitrogen, zinc, and copper—that roots alone cannot access efficiently.

Main Types in UK Gardens

1. Arbuscular Mycorrhizal Fungi (AMF / Endomycorrhizae)
   • Most common.
   • Associate with ~70–80% of plants, including most vegetables (tomatoes, beans, carrots, onions), strawberries, lawns, grasses, and many flowers.
   • Hyphae enter root cells and form arbuscules for nutrient exchange.
2. Ectomycorrhizal Fungi
   • Form a sheath around roots and a net between cells.
   • Common in woody plants: oaks, birches, pines, spruces, beeches, willows.
   • Often produce visible mushrooms or truffles.

Which Plants Benefit (and Which Do Not)

Benefit from standard AMF or ectomycorrhizae:

• Vegetables: tomatoes, peppers, beans, peas, carrots, onions, potatoes, strawberries.
• Fruits: apples, many berries (except blueberries/cranberries).
• Flowers: roses, dahlias, most herbaceous perennials.
• Lawns and grasses.
• Trees/shrubs: oaks, birches, pines, spruces, willows.

Do not form associations or gain little benefit:

• Brassicaceae family: cabbages, broccoli, kale, Brussels sprouts, cauliflower, radishes, mustard.
• Beets, spinach (Chenopodiaceae in many cases).
• Ericaceous plants: rhododendrons, azaleas, blueberries, cranberries, heathers (use specialist ericoid mycorrhizae instead).
• Some others: carnations, certain sedges.

Adding standard inoculants to non-mycorrhizal plants is ineffective.

Key Benefits (with Evidence from Studies)

• Improved nutrient uptake (especially phosphorus): AMF increased leaf phosphorus in maize by 33.86% (Lu et al., 2023).
• Better drought resistance: AMF raised plant biomass under drought and nutrient uptake (N by 23.74%, P by 135.61% at high C:N ratios) (Zaman et al., 2024).
• Enhanced disease resistance: AMF increased plant height by 24.83%, lignin by 141.65%, and flavonoids by 44.61% in Lycium barbarum against root rot (2024 study).
• Stronger establishment: Common mycorrhizal networks improve seedling survival and early growth under stress (Figueiredo et al., 2021).
• Reduced fertiliser need: AMF biofertilisers can cut chemical fertiliser use by up to 50% while maintaining or increasing yields (Alam et al., 2024).
• Improved soil structure: Hyphae and glomalin bind aggregates, reduce erosion, and enhance aeration (Fall et al., 2022).

How to Use in UK Gardens

Commercial mycorrhizal products are available, such as the premium endo/ecto mycorrhizal fungi inoculant from Dr Forest (available at www.drforest.co.uk/products/mycorrhizal-fungi). Apply powder directly to roots or in the planting hole at planting time—contact is required. One application usually lasts the plant's life.

Avoid high-phosphorus fertilisers and most fungicides, which harm the fungi. No-dig methods, mulching, and reduced tillage help maintain natural populations.

In disturbed or heavily fertilised soils, natural levels are often low, so inoculation at planting is useful for compatible plants.

Summary

Mycorrhizal fungi improve plant performance in nutrient-poor or dry conditions common in the UK. Use them selectively on compatible species for stronger growth, lower inputs, and better soil health.