If you want healthier plants with stronger roots and better blooms, learning how to add mycorrhizal fungi to soil is a game-changer. This simple step helps your garden work with nature, not against it.
Mycorrhizal fungi are tiny, beneficial organisms that form a partnership with plant roots. They extend far into the soil, acting like a super-charged root system for your plants. In return for sugars from the plant, they deliver water and nutrients like phosphorus and nitrogen. It’s a win-win that leads to less watering, fewer fertilizer needs, and plants that can handle stress much better.
How to Add Mycorrhizal Fungi to Soil
Adding these fungi isn’t hard, but doing it correctly makes all the difference. The key is to get the fungi in direct contact with the plant’s roots. They need to physically connect to work there magic. Here are the main methods, from simplest to most involved.
Method 1: Adding Fungi During Planting
This is the easiest and most effective time to introduce mycorrhizae. You have the roots right there, ready for contact.
- Dig your planting hole as you normally would.
- Take your mycorrhizal product (a powder, granular, or liquid) and sprinkle or pour the recommended amount directly into the hole.
- Gently mix it into the soil at the bottom and sides of the hole.
- Place your plant in the hole, ensuring the roots touch the treated soil.
- Backfill and water well to activate the fungi.
Method 2: Applying to Existing Plants
You can still add mycorrhizae to plants already in the ground or in pots. It takes a bit more care to get it to the root zone.
- For trees and shrubs: Use a soil probe or a narrow trowel to create several deep holes in the soil around the drip line (the area under the outer branches). Fill the holes with the mycorrhizal product and then water.
- For perennials and garden beds: Lightly scratch the product into the soil surface around the base of the plants, then water thoroughly. Try to avoid major disturbance of existing roots.
- For potted plants: Mix the product into the top inch of soil or, for a more thorough treatment, consider carefully repotting with fresh, treated mix.
Method 3: Mixing Into Potting Soil
For container gardening, this method ensures every plant gets a boost from the start.
When you’re preparing a large batch of potting mix for pots or raised beds, simply add the recommended amount of mycorrhizal inoculant to the soil and mix it well. Then use the treated soil as you normally would for potting or filling beds. This is a very efficient approach.
Choosing the Right Mycorrhizal Product
Not all products are the same. Look for one that contains a blend of different mycorrhizal species, as different plants prefer different partners. Endomycorrhizae (like Glomus species) work with most common garden plants, vegetables, and flowers. Ectomycorrhizae partner with trees like pines, oaks, and firs. A good blend will cover most of your garden’s needs.
When and How Often to Apply
You only need to apply mycorrhizal fungi once per plant, at planting time or as a one-time treatment for established plants. The fungi will establish themselves and grow along with the root system. Reapplication is generally not necessary unless the soil is severely disturbed or replaced. The best time to apply is during the active growing season (spring or fall) when roots are growing and can quickly form the partnership.
Creating a Fungus-Friendly Garden
Adding the fungi is just the first step. To keep them thriving and working for you, you need to support their environment.
Soil Practices That Help Mycorrhizae
- Avoid Excessive Tilling: Tilling soil breaks up the delicate fungal networks. Practice no-till or low-till gardening where possible.
- Go Easy on Chemical Fertilizers: High levels of soluble phosphorus (the middle number on a fertilizer bag) can tell plants they don’t need the fungi. Use organic, slow-release fertilizers and compost instead.
- Use Less Fungicide: Broad-spectrum fungicides can harm beneficial fungi. If you must use one, choose a targeted product and apply it carefully.
- Add Organic Matter: Compost and well-rotted manure provide a fantastic food source for the entire soil food web, including your mycorrhizal fungi.
Plants That Benefit Most
Almost all plants benefit, but some are especially dependent. These include:
- Most vegetables (tomatoes, peppers, squash, onions)
- Fruit trees and berry bushes
- Annual and perennial flowers
- Lawn grasses (especially when seeding or sodding)
A few plants don’t form these relationships. The main exceptions are plants in the brassica family (like broccoli, kale, and cabbage) and the amaranth family (like spinach and beets). It’s fine if they get some, but they won’t use it.
Common Mistakes to Avoid
Even with good intentions, it’s easy to make a few errors that reduce the effectiveness of your mycorrhizal application.
1. Letting the Product Expire or Storing It Poorly
Mycorrhizal products contain living organisms. Check the expiration date and store them in a cool, dark place. Don’t leave the bag open or in the hot sun.
2. Applying to Dry Soil and Not Watering
The fungi need moisture to become active and grow. Always water the area thoroughly after application. Dry soil will render the treatment useless.
3. Using Old, Sterilized Potting Mix
Sterilized or “soilless” potting mixes often contain no living biology. These are perfect candidates for adding mycorrhizae, but avoid using mixes that are years old or have been stored poorly.
4. Disturbing Treated Soil Too Much
After application, try to minimize digging in the area. You want the network to establish without being broken apart.
FAQ: Mycorrhizal Fungi in Your Garden
Can I make my own mycorrhizal fungi?
It’s not practical for most gardeners to culture pure mycorrhizal fungi at home. The most reliable method is to purchase a reputable product. However, you can encourage native fungi by avoiding harsh chemicals and adding lots of compost.
Is mycorrhizal fungi safe for all my plants?
Yes, it is completely safe and organic. It is not a fertilizer or chemical, but a natural organism that forms a mutual relationship with plant roots. It won’t harm any plants, even those that don’t form associations.
How long does it take to see results?
You won’t see results overnight. The fungi need time to colonize the roots. Often, you’ll notice improved growth, flowering, or stress resistance in the following growing season. The benefits build and last for the life of the plant.
Can I use to much mycorrhizae?
It’s very difficult to “overdose.” The fungi will only colonize as many roots as are available. Using more than the recommended amount is generally a waste of product, but it won’t hurt your plants.
Does it work in all types of soil?
Mycorrhizal fungi work in a wide range of soils, but they thrive best in soils with good organic matter. They struggle in very waterlogged, compacted, or sterile soils. Improving your overall soil health will always make them more effective.
Adding mycorrhizal fungi is one of the simplest yet most profound things you can do for your garden’s health. It connects your plants to the soil in a powerful way, reducing your workload and increasing your gardens resilience. By following these steps to get the fungi to the roots and then supporting their habitat, you’re investing in a healthier garden ecosystem for seasons to come. Give it a try with your next planting project—your plants will thank you for it.