It's ALIVE! Soil and Mycorrhiza

Mighty Mycorrhiza – Super soil staple or snake oil scam?

By Amy McDowell

Promises, promises. We’ve all heard advertisements making promises about some amazing new product and what it can do for our homes, our lives, our gardens. A healthy spirit of skepticism has become part of our nature.

So what is the scoop on mycorrhiza? At least 25 mycorrhiza products are available in garden centers across the U.S.—oddly named products like Myke and Myco Stim to name just a couple. What are these products, and what will they do for your garden?

Mycorrhiza is a beneficial relationship between plants and fungus. “Mycorrhiza is a natural part of the soil and a part of plant nutrient uptake,” writes Ted St. John, Ph.D. in The Instant Expert Guide to Mycorrhiza, 2000. “The fungi are the dominant soil microorganisms, and soil biology depends heavily upon the presence, density, and types of mycorrhizal fungi.”

Mycorrhizal fungi are easily destroyed when the plants are removed and the soil disturbed. “They are always missing from freshly graded sites,” St. John writes.

Adding mycorrhizal fungi spores to your soil (called inoculating) will not necessarily produce big, robust plants, as many of the products claim. Being familiar with soil biology, I was thrilled when companies began packaging micorrhizae for home gardeners. In recent years I’ve tried several of the products in my garden without noticeable results. Although there are greenhouse and field studies that show amazing differences in plant growth, I’ve learned that it’s unlikely that you would notice differences like that in a trial in your own garden.

“Plant growth response in itself is not likely to tell the story. If uninocculated plots have been kept healthy by fertilization, any mycorrhizal effects will have been masked,” St. John writes.

Realistically, you can expect inoculated plants to be stronger, better able to survive harsh weather conditions, and protected from disease. Your site will be more resistant to invasion by weeds and most important, mycorrhiza will improve soil structure.

St. John recommends looking for a “propagule” or spore count on the label so you know what you are getting for your money. Mix the micorrhiza product with seeds as you sow or apply it to all sides of the root ball as you put plants in the ground. You can sprinkle mycorrhizae over the surface of the soil or till it in, but it doesn’t begin working until it connects with live plant roots.

Although he warns gardeners to be wary of hype and exaggerated claims, St. John solidly backs mycorrhiza as beneficial for gardens. “What is very clear, from every study that has done the tests, is that inoculation is greatly superior to no inoculation,” he writes.

The soil -- It's ALIVE!

Small plants + live soil = big rewards

By Amy McDowell

A trend has hit the perennial garden scene with a lot of force in recent years. The idea is to focus your money and energy on amending the soil and spend less money and energy on the plants.

After two decades of installing perennial gardens, author Tracy DiSabato-Aust has shown that perennials can double or triple in size during their first season—if the soil has been amended with organic matter. She convinces clients of her Ohio design and installation firm that investing in the soil is the top priority. To offset the expense of soil amendments and site preparation, she plants 4-inch (and sometimes even bare-root) perennials. Believe it or not, her tiny perennials outperform gallon-size perennials within a single season. In following years, the plants are naturally healthier and more robust because of the live soil. Photos documenting the amazing growth are included in her book, “The Well-Tended Perennial Garden”. (Timber Press, 1998)

Live soil isn’t some mushy black matter you can buy in a bag for 99 cents. Live soil has billions of bacteria, millions of fungi, plus protozoa, paramesei and nematodes—all in a single spoonful. Organic matter is the key to live soil, because it provides food for the bacteria, fungi and microbes.

Landscape Architect Terry Guen, who coordinated the design and construction of the 25-acre Millennium Park in downtown Chicago, said they purchased live soil for the park from a site in Indiana. With guidelines for soil handling and storage, they kept it healthy and alive throughout construction. They were careful not to smother or compact it by piling it too deep or driving over it with heavy equipment. As the world’s largest millennium project, planners insisted on large plants for the site, but the care they took on buying and maintaining healthy, live soil is noteworthy.

When building a new bed in your garden, add life to your soil with organic matter. Sprinkle two pounds of bone meal per 100 square feet, then add a 4-inch layer of organic matter such as compost, sphagnum peat moss or leaf humus. Till it in as deeply as the tiller will go, rake it smooth, and you are ready to plant your little ones. Then step back and watch them leap.

Composting Leaves

Keep Your Leaves

By Amy McDowell

Asters, mums, and plump orange pumpkins are adorning our porches and perching on our steps.  There are corn stalks, straw bales, and gourds – evidence of a generous fall harvest.  It’s beginning to look a lot like autumn – everywhere you go.

This is a great time of year to begin that compost pile you’ve been thinking about.  Composting is simple, and it keeps valuable resources on your lot that you can never replace, no matter how much money you spend.

Healthy soil is loaded with organic matter – that is, decaying plant debris – and all kinds of microscopic organisms. One gram of healthy soil will have 37 billion bacteria and 4 million fungi, plus larger organisms like protozoa, paramesei, and nematodes. Healthy soil means healthy plants, whether they are flowers, shrubs, trees, or turf.

Composting can be as simple as raking your fall leaves into a pile and tossing a few shovels full of soil on top. The leaves will break down more quickly if you shred them first. There are several styles of inexpensive leaf shredders on the market, or you can shred the leaves by running over them with your bagging mower. Shredding the leaves is not necessary, but it is helpful and speeds up the composting process.

If you are wondering where to get the extra soil, consider digging a shallow pit for your leaves and leaving the excess soil around the edges to sprinkle over the top.

You can always till leaves directly into your garden or spread shredded leaves across the surface if you don’t want to make a compost pile. Whatever your method, the key is to keep your leaves, grass clippings, and all of your yard waste except sticks and branches.

Why is your yard waste such a valuable resource for your yard?  In the soil, bacteria and fungi break down plant debris into smaller and smaller pieces for microbes to feed on.  With no plant debris, there is no food source. The soil is unhealthy and barren. In the typical urban environment, the soil is starving because there is no organic matter. Chemical fertilizers are a temporary fix, and they cannot replace precious organic matter.

If you live in an area where the soil has been disturbed by new construction, rest assured that the soil can recover, but it may take decades. The more organic matter you can add to the soil, the more quickly the soil organisms can heal the damage.

As the trees are beginning to shed their leaves, now is a wonderful time to begin composting and recycling your yard’s priceless resources.

Amy McDowell is an Iowa Certified Nursery Professional. She has an associate’s degree in commercial horticulture and has worked in the field for ten years. She lives and gardens in Polk County.