As the kingdoms of life go, fungus gets a bad rap. Plants and animals get our attention and our love, but fungi are generally associated with death and decay.
Molds are a sure sign of decomposition, and even the friendliest fungus, the mushroom, can be poisonous.
As such, you might be forgiven for thinking that the only place the green industry runs into fungus is as a disease to be driven off by chemical application. This, however, is far from the truth. The lawns you tend to on a daily basis contain hardier, stronger plants, thanks to one fungus in particular, mycorrhizae.
Mycorrhizal fungus is the most important organism found in soil, and it’s been there for hundreds of millions of years. The word mycorrhizae comes from two Greek words: mycos, meaning “fungus,” and rhiza, meaning “roots.” That gives you a pretty good idea of what it is, both a fungus and a root at the same time.
Mycorrhizal fungi is no wallflower; it gets around, establishing a symbiotic relationship with the roots of just about every plant on Earth, including grasses, grains, flowers and trees. There are two main categories of mycorrhizae: endomycorrhizae and ectomycorrhizae. If it makes it easier to remember which is which, the prefix ‘endo’ means inside, and ‘ecto’ means outside.
“The endomycorrhizae literally attaches itself to the roots, penetrates cell walls, and becomes one with the roots,” said Robert Neidermyer, PhD, director, soil and plant science at Holganix, a soil-amendment manufacturer based in Glen Mills, Pennsylvania. “The ectomycorrhizae just kind of lay up next to the roots, coming into very close proximity, but don’t attach themselves.”
Of the two players, endomycorrhizae is by far the most popular. Approximately 80 to 90 percent of all plants in the world form symbiotic relationships with it. These include a wide variety of green, leafy plants and cultivated grasses, as well as many dryland, wetland, aquatic and riparian species.
Ectomycorrhizae, on the other hand, forms symbiotic relationships with only about five percent of all the plants in the world. These are mainly tree species, including pine, spruce fir and hardwoods such as oak and birch. Some commercially important plant species also benefit from linkage with ectomycorrhizae.
Plants need three things to survive: sunlight, water and nutrients.
Mycorrhizae functions as a delivery system for the latter two. The plants and the fungi work together as a single, functioning unit. The plants perform photosynthesis above the ground, while the mycorrhizae colonize the roots below the ground, sending tiny filaments far out into the soil, well beyond the roots they’ve colonized.
Deeper roots can make a big difference in getting a plant the resources it needs, but it can’t make nutrients where they don’t exist. “If you’ve got poor soil with very little nitrogen or any other nutrients in it, and no mycorrhizae and bacteria either, you have to figure out a way to add them back in, or your plants just won’t do very well,” said Dennis Richmond, owner and CEO of Richmond Hydromulch and Seeding, LLC, in Wylie, Texas.
One common way to help the soil is to put those nutrients back in directly. “Fertilizers are nutrients—nitrogen (N), phosphorus (P), and potassium (K),” said Neidermyer. “The N, P and K numbers you see on the bag are the inert chemical elements that are used to grow plants; they cannot grow without them.”
“Mycorrhizae and bacteria act as probiotics for the soil,” he said. “They’re microorganisms that exist in association with plants and help them function, picking up nutrients and moisture for them. They aren’t fertilizers, as they aren’t chemicals; they’re actual, living organisms.” In other words, mycorrhizae act as “fertilizer helpers,” bringing the nutrients in the fertilizer right to the plants’ roots.
Some symbiotic relationships in nature benefit one of the partner species much more than the other one. But the plant-mycorrhizal partnership is an equal union that both sides benefit from greatly.
As the filaments grow and stretch out, they behave like military reconnaissance squads, conducting sweep searches for water and nutrients over a large underground area. Once the water and nutrients are found, the filaments transport them directly back to the roots of the plants. In return, the plants, through photosynthesis, reward the mycorrhizae with the glucose it needs to thrive.
For plants, the major advantage of this relationship is an enhanced supply of available nutrients, including carbon, potassium, phosphorus and nitrogen. They also get a faster uptake of minerals, such as calcium, copper, iron and zinc, and in greater amounts than would normally have been available to their roots.
The presence of mycorrhizae also gives plants an increased tolerance to adverse soil conditions. The plants can continue to grow and do much better than they would without the fungi’s help, even in degraded, nutrient-deficient soils, or soils with lower-than-ideal pH and higher-than-ideal soil temperatures.
Plants have better root formation, fewer root diseases and soil-pest problems and require less fertilizer when mycorrhizae is around. “There isn’t as much of an opportunity for pathogens looking to come in and impact the plants in a negative way, when you have a good mycorrhizae base,” said Barrett Ersek, founder and CEO of Holganix, “so fungus and disease pressure become much less of an issue.”
They also need less water. The filaments the fungus sends out have the ability to take up moisture from much deeper in the soil, beyond the reach of the plant’s roots.
Mycorrhizae varieties don’t need much water themselves, but their filaments will continue seeking it for the sake of the plants, enabling those plants to survive dry spells that would otherwise be fatal.
In an optimal scenario, a healthy organic lawn tended by mycorrhizae will be a slow-growing lawn.
Synthetic fertilizers result in fast growth, which is good when you need quick results, but carries a cost on the maintenance end. “You’re going to then need to cut more frequently, or you’re going to need to cut the lawn more slowly, because you’ve got more clippings to deal with, and you have to move the machine slower,” said Ersek.
That means more frequent maintenance visits, longer visits, or both. A growth with deep roots, that is both green and slow, will save you money. Try it for yourself, and you may find that what you save mowing may outweigh what you spend on ensuring that slow growth.
Of course, where the fungus really shines is in helping to establish new plantings. Trying to set a plant into a landscape always carries an element of risk. We minimize these risks by optimizing the conditions as much as we can. We mulch, we irrigate, we fertilize, and we pray that the roots grow strong and deep as quickly as they can. Adding mycorrhizae to the soil is another way to ensure the job won’t fail.
Topsoil that’s been disturbed by construction just isn’t the same afterwards. Among other things, its natural mycorrhizal content will be significantly diminished. If those fungi aren’t replaced, it’ll be more difficult for vegetation to reestablish itself on that site.
Some reclaimed and reused topsoil is biologically active enough to provide sufficient mycorrhizal content. If good topsoil is present on a site before its disturbed, it can be preserved by removing it and stockpiling it somewhere nearby.
However, this stockpiling is often done incorrectly, with soil piled up in tall, vertical rows and left alone for long periods of time. Only the very upper levels of the piles remains biologically active; the remaining 80 percent of the soil is dead. New topsoil can be hauled in, but that’s usually very expensive.
“If they pulled soil out of the subsurface from ten feet down, brought that up to the top, and that became the topsoil, you’d probably have some mycorrhizal issues,” said Richmond.
A cheaper solution is to bring the existing topsoil back to life by adding soil amendments that can replace the missing mycorrhizae. Verdyol Biotic Earth and Holganix are two examples, but there are many others.
Verdyol Biotic Earth incorporates sustainably-harvested sphagnum peat moss as its main organic component. The sphagnum moss is supplemented with straw, flax fibers, and precise amounts of mycorrhizae, selected because they work well with sphagnum peat moss.
“Holganix contains 20 different species of both ecto- and endo-mycorrhizae,” said Neidermyer. “That pretty much covers all the different types of plants that would be used in hydroseeding applications. There are separate formulations, depending on what mixture of grasses and/or wild seeds you’re using.”
Robert Arello, owner and president of Hydrograss Technologies, Inc., of North Oxford, Massachusetts, and Sarasota, Florida, doesn’t think adding mycorrhizae alone is the answer.
“We’ll use combinations of mycorrhizae with other things, like humic acid, either in a dry or liquid state,” he said. “We also use Sustain’s organic turkey manure, and Bioprime, a product that has a combination of slow-release fertilizers and a plant-growth promoter that softens seed coats.” (Some mycorrhizae supplements already contain humic acid.)
Ersek warns against adding too much humic acid, especially in a very concentrated form. It could cause a burn. As for mycorrhizae, however, “You can’t possibly put too much down. It won’t hurt anything.”
However, he does say that when you’re talking about adding biostimulants—Holganix is one— you’ve got to think about everything else you’re putting in the tank; specifically, fertilizer. Remember that you’re greatly increasing the efficiency in which those plants uptake the N, P and K.
“If you’ve put down too much fertilizer and then add a biostimulant, you’ll accelerate that burning effect, because you’ve just turbocharged it,” Ersek cautions. “And there are some other chemical additives that get enhanced with biostimulants which can also add burn potential.”
If you’ve never added a biostimulant product to your hydroseeding mix before, Ersek advises cutting the fertilizer back by 50 percent. Some of his hydroseeding contractor customers with more experience using such products cut their fertilizer rates back even further.
Arello says that with denser, more claylike soils, hydromulching alone may not be adequate. “We had that problem with one particular site. We actually punched holes into the dirt, scarified it so we could really work that mycorrhizae down in there.”
Ersek says that it doesn’t matter whether you use jet or mechanical agitation, either. Yes, mycorrhizae are living organisms, and some may get beaten up or even killed by paddle agitation, but the collateral damage is so tiny that it’s not really a concern. As far as killing mycorrhizae goes, Arello says that sites with salty well water are much more likely to commit mycorrhizae-cide.
Amendments like these can be added directly to hydroseeding mixes and applied to sites even where there is little or no topsoil— or water—present. When hydroseeding, you’re usually not applying any additional water, other than that used to make the slurry itself.
You can see how the fungi’s water-seeking ability is a big plus here. If you’re hydroseeding in a drought-stricken area, or one where irrigation is either not allowed or not available, the addition of mycorrhizae could be the single biggest factor in the success of that project.
We’ve spent a lot of time talking about mycorrhizae, but we shouldn’t close before mentioning the importance of soil bacteria. “It’s the bacteria that promote early germination,” said Neidermyer.
“As soon as a seed germinates, the very first thing that gets going are its roots,” he said. “The mycorrhizae associate with the roots, and that’s important, because you need to bring water and nutrients to the newly germinated, emerging plant so it can thrive.”
Soil amendments containing mycorrhizae help vegetation not merely get established, but off to a great, healthy start. Adding mycorrhizae to a hydroseeding mix will help the seeds derive maximum benefit from the fertilizer that was applied along with them. And, it can do it using less water, and at less than half the cost of hauling in brand new topsoil from far away.
You work every day to try to build a good foundation for beautiful, healthy landscapes. Too often, you have to compromise between making progress towards this goal, and keeping up a lawn’s appearance, when that lawn won’t look good with strictly organic methods. If you can make that compromise less difficult by including mycorrhizae in your toolbox, why wouldn’t you?