If your vegetable garden produces average results despite regular watering and feeding, the missing piece may be underground. Root fungi called mycorrhizae have partnered with plant roots for 400 million years, expanding the root system's nutrient reach up to 1,000 times and pulling in phosphorus, nitrogen, and water that roots alone can't access. The problem: most vegetable garden soils have had their mycorrhizal populations wiped out by tilling, synthetic fertilizers, and compaction. This page explains what root fungi actually do, which vegetables respond to them, and the correct way to apply them at planting time.
In short:
- Root fungi called mycorrhizae attach to vegetable roots and expand their nutrient reach up to 1,000 times
- Most vegetables benefit — but brassicas (broccoli, kale, cabbage) and beets don't form mycorrhizal relationships at all
- Most cultivated garden soil has lost its mycorrhizal populations through tilling, synthetic fertilizers, and compaction
- Apply mycorrhizal inoculant directly to seeds or roots at planting time — adding it to established plants is far less effective
What Are Mycorrhizal Fungi (And Do They Have Roots)?
Mycorrhizal fungi - called mycorrhizae, from the Greek for "fungus" (mukés) and "roots" (rhiza) are organisms that form a close, mutually beneficial partnership with plant roots. Despite the name, fungi themselves don't have true roots. Instead, they grow thread-like structures called hyphae that extend outward from the plant's roots into surrounding soil, functioning like roots by absorbing water and nutrients from spaces too small for actual roots to reach. Certain kinds have occurred naturally in soil for more than 400 million years.
There are two main types relevant to vegetable gardeners. Endomycorrhizae (also called arbuscular mycorrhizae) penetrate inside the root cells and work with most vegetables, fruits, and herbs. Ectomycorrhizae form a sheath around the outside of the root and are associated primarily with trees. For vegetable gardening, endomycorrhizae are almost always the relevant type. For more detail on endomycorrhizal fungi specifically, see this Q&A on identifying and using endomycorrhizal fungi with vegetables.
How Root Fungi Feed Your Vegetables?
Once mycorrhizal fungi colonize a plant's roots, they extend hyphae outward through the soil - reaching phosphorus, nitrogen, calcium, magnesium, and water stored in soil pores too small for roots to enter directly. This can expand the root system's effective surface area by 10 to 1,000 times, depending on conditions. The plant gets nutrients it couldn't access on its own. In return, it supplies the fungi with carbohydrates produced through photosynthesis - a trade that sustains both partners throughout the growing season.
As a secondary benefit, mycorrhizal fungi produce a sticky protein called glomalin that binds soil particles together. Over time this improves soil structure, water retention, and aeration - the fungi are improving your soil even as they feed your plants.
Why Most Vegetable Garden Soil Lacks Mycorrhizal Fungi?
Ninety-five percent of the world's undisturbed plant species have mycorrhizal partners in their root systems. Most cultivated vegetable garden soil does not. The gap comes down to a few common practices.
Tilling is the biggest culprit - mycorrhizal hyphae are fragile and take weeks to form a working network; a single pass with a tiller breaks them apart. Synthetic phosphorus fertilizers create a different problem: when the soil already has abundant phosphorus, the plant stops investing carbohydrates in feeding the fungi and the relationship collapses. Soil compaction limits the oxygen that fungi need, while bare soil between growing seasons eliminates the host roots that keep fungal populations alive. The result: most garden beds start each season with very low mycorrhizal activity, and the plants growing in them never get the underground support they would have in undisturbed soil.
Which Vegetables Benefit From Root Fungi — and Which Don't?
Most common vegetables form strong mycorrhizal relationships. A small but important group does not — and applying inoculant to them is wasted effort.
Vegetables that DO benefit:
Tomatoes, peppers, eggplant, squash, zucchini, cucumbers, pumpkins, melons, beans, peas, corn, carrots, onions, garlic, leeks, lettuce, and most herbs all form endomycorrhizal relationships and respond well to inoculant applied at planting time.
Vegetables that do NOT benefit:
- Brassicas: broccoli, cabbage, kale, cauliflower, Brussels sprouts, turnips, radishes, arugula
- Beets, spinach, Swiss chard
These families evolved without mycorrhizal relationships. Adding inoculant to them produces no effect. Save the product for the plants that actually use it.
How to Apply Root Fungi at Planting Time?
The products containing Mycorrhizae are most often applied as part of the planting process. The Mycorrhizae are sprinkled into the hole before the plant is placed in the hole. Some products can be applied around existing plants. For details see the instruction with the product descriptions in Tool Shed linked below.
MYKE® is used for fruits, vegetables and culinary herbs, when transplanting seedlings or sowing seeds indoors or outdoors. It ensures an abundant and bountiful harvest of superior quality. It contains mycorrhizae on a natural fine granulated carrier (compost and peat) providing a good seed germination environment.
Instructions For Use With Seeds
1. Turn over soil
2. Spread a layer of MYKE in the bottom of furrow.
3. Sow seeds
4. Cover with soil, water thoroughly
Instructions For Use With Seedlings
1. Turn over soil and dig a hole according to the root ball size.
2. Apply a layer of MYKE on the sides and bottom of the hole
3. Be sure that the new roots are in contact with the product.
4. Cover with soil and then water well.
When using MYKE growth supplements ( called MYCORISE™) only one application is needed. The product should be placed as close to the roots or the root zone as you can so the roots can be colonized by the fungus in the product. It takes about 4 weeks for this to happen. As the roots grow, the mycorrhizae will develop and multiply along with those expanding roots.
MYKE Vegetable Garden is available in 1.4 quart (for 95 plants) and 3.6 quart (for 265 plants) containers.
For more information and a retail source go to Web Site for MYKE
Common Questions About Root Fungi and Mycorrhizae
Do fungi have roots?
Fungi don't have true roots like plants do. Instead, mycorrhizal fungi grow thread-like structures called hyphae that extend outward from plant roots into the surrounding soil - functioning like roots by absorbing water and nutrients from spaces too small for actual roots to enter. The hyphae network can expand a plant root's effective surface area by 10 to 1,000 times, which is why mycorrhizal fungi are sometimes described as "roots of the roots."
Which vegetables don't benefit from mycorrhizal fungi?
Vegetables in the brassica family - broccoli, cabbage, kale, cauliflower, and Brussels sprouts - don't form mycorrhizal relationships, so applying inoculant to them has no effect. Beets, spinach, and Swiss chard also don't respond. Most other common vegetables including tomatoes, peppers, squash, cucumbers, corn, beans, and carrots benefit significantly from mycorrhizal inoculant applied at planting time.
How do mycorrhizal fungi feed vegetables?
Mycorrhizal fungi attach to vegetable roots and extend hyphae outward into the soil, scavenging phosphorus, nitrogen, calcium, and water from pores too small for plant roots to reach. This can expand the root's effective nutrient-gathering area by up to 1,000 times. In return, the plant supplies the fungi with carbohydrates produced through photosynthesis, a trade that benefits both partners. The fungi also produce a protein called glomalin that binds soil particles together, improving soil structure as a side effect.
Why does my garden soil lack mycorrhizal fungi?
Tilling is the main cause - it physically breaks apart the hyphae networks mycorrhizal fungi spend weeks building. Synthetic phosphorus fertilizers suppress the relationship because the plant no longer relies on the fungi to access phosphorus. Soil compaction, chemical pesticides, and bare soil between growing seasons reduce populations further. Undisturbed natural soils almost always have thriving mycorrhizal networks; most cultivated vegetable beds don't.
Getting Root Fungi Right in Your Vegetable Garden
Adding root fungi at planting time is one of the few soil interventions that keeps working all season, once the mycorrhizal network is established, it continues feeding your vegetables without additional effort. The key is timing: apply inoculant directly to seeds or root balls at the moment of planting, before the root system has a chance to develop without fungal partners. If you're also feeding with synthetic fertilizers, hold off on high-phosphorus products for the first few weeks - they suppress the very relationship you're trying to build. Get the soil biology right first and you'll need less of everything else.
