Key Takeaways
- These fungi extend your plant’s roots by 100x–1,000x, reaching water and nutrients that roots physically cannot access.
- They unlock chemically bound Phosphorus from soil using enzymes your plants don’t produce.
- They regulate water channels during drought, giving plants a survival advantage during heat waves.
What Actually Is Mycorrhizae? (Simply Explained)
Most garden soil is dead. You’ve been dumping fertilizer on it for years, and the microscopic life that should be feeding your plants has been wiped out.
Arbuscular Mycorrhizal Fungi (AMF) from the phylum Glomeromycota are the microscopic repair crew. They’re obligate biotrophs, meaning they can’t survive without a living root to colonize. Once attached, they penetrate root cells and build tree-like structures called arbuscules.
Think of it as a barter system: Your plant trades sugar (which it makes through photosynthesis) for water and nutrients the fungi collect. The fungi send out thread-like hyphae that act like the “Internet of the Soil,” connecting your plants to resources inches or even feet away.
Here’s the problem with bag fertilizer: When you dump high-Phosphorus synthetic fertilizer on your soil, the plant shuts off the chemical signal that calls the fungi. Why trade sugar when free nutrients are flooding in? But once that fertilizer washes away, your plant is left with shallow, weak roots and no fungal network to fall back on.
The 3 Real Benefits (Beyond Just “Growth”)
1. The “Drought Shield” (Aquaporins)
Your plant’s roots can only fit into soil pores larger than their diameter. During drought, water hides in micropores that roots simply cannot reach.
AMF hyphae are 1/10th the diameter of the smallest root hair. They slip into these tiny spaces, find water, and transport it back. Even better, the fungi regulate aquaporins—protein channels in plant cells that control water flow. This gives your plants a physiological advantage during heat waves, keeping them hydrated when others wilt.
2. Phosphorus Unlocking
Phosphorus doesn’t move through soil. It binds chemically to calcium, iron, and aluminum, forming compounds your plant roots cannot access. This creates a “depletion zone” around each root where all available Phosphorus has been absorbed.
However, phosphorus availability is also strongly influenced by soil pH, which determines whether these compounds remain soluble or become locked out of reach
AMF produce enzymes (phosphatases) that break these chemical bonds and release the Phosphorus. Their hyphae extend far beyond the depletion zone, mining nutrients from soil your roots will never touch. This is why plants with AMF colonization can thrive in low-fertility soil where others starve.
3. Glomalin (The Soil Glue)
AMF produce a sticky protein called glomalin that coats their hyphae. This protein glues soil particles together, creating stable aggregates that resist erosion and improve drainage.
Over time, glomalin builds soil structure. Your soil becomes fluffier, holds water better, and resists compaction. This is a multi-year investment, not an instant fix.
Which Plants Need It? (And Which Don’t)
About 90% of plants form associations with AMF. But some families evolved without them and actually reject colonization.
If you apply AMF to plants that don’t use it, you’re burning money. Check this table before you buy.
| Plant Family | Status | Examples |
|---|---|---|
| Solanaceae | Host | Tomato, Potato, Pepper, Eggplant |
| Brassicaceae | Non-Host | Broccoli, Cabbage, Kale, Cauliflower, Mustard |
| Fabaceae | Host | Peas, Beans, Clover |
| Chenopodiaceae | Non-Host | Spinach, Beets, Chard |
| Cucurbitaceae | Host | Cucumber, Squash, Melon, Pumpkin |
| Ericaceae | Requires Different Fungi | Blueberries, Azaleas, Rhododendrons |
Blueberries and azaleas need ericoid mycorrhizae, not arbuscular. Don’t waste AMF products on them.
Buyer’s Guide: Spores vs. Propagules
This is where most gardeners get scammed. Read the label carefully.
Spores are dormant. They need specific temperature and moisture conditions to germinate, and colonization can take 3–6 weeks. Cheap products sell you pure spores because they’re easy to mass-produce.
Propagules are root fragments already colonized with live fungi. They establish within days because the fungi are already active. Look for products listing “propagule count” or “infective propagules per gram.” These cost more but work faster.
Store your AMF in a cool, dry place. Temperatures above 120°F (49°C) kill the fungi instantly. Do not leave the bag in your car during summer, and don’t store it in a hot garage. The fungi will be dead before you ever open the package.
How to Apply It (Specific Dosage)
AMF must contact roots to colonize. Sprinkling it on top of the soil does nothing. UV light from the sun kills the fungi, and even if it survives, it can’t find roots on its own.
Method 1: The Root Dip (Best for Transplants)
Mix 1 teaspoon of AMF powder per gallon of water. Dip the roots of your transplant into the solution for 10 seconds before planting.
This ensures every root hair gets coated with fungi. Colonization starts within 48 hours.
Method 2: The Planting Hole
Dig your hole, place 1 tablespoon of AMF powder at the bottom, then set the transplant on top. The roots must physically touch the powder.
Backfill with soil and water immediately. The moisture activates the fungi and kicks off colonization.
Frequently Asked Questions
Q: Can I sprinkle it on top of the soil?
No. UV light kills the fungi within hours, and they need direct root contact to colonize. Surface application is a waste.
Q: Will it work on my lawn?
Only if you aerate first. Grass roots need to contact the fungi. Core aerate your lawn, then spread AMF powder into the holes. Water heavily to wash it down to the root zone.
Q: Does it expire?
Yes. Spores lose viability after 18–24 months. Check the manufacture date on the package. Old product won’t colonize, and you’ll see no results.