How A Fungus Can Be Beneficial To Growing Plants In Your Landscape
By Al Will - Professor Emeritus
For millions of years “mother nature” has done a superb job. Just look at
our relatively undisturbed national parks and other natural habitats that have
been preserved for our enjoyment and you will see healthy plants. “Mother
nature” has produced a living soil, filled with wonderful microbial populations
of beneficial bacteria, fungi, nematodes and protozoans that supply the plant
with all of the necessary nutrients for healthy growth. In your last copy of
the F. G. bulletin we talked about the beneficial soil bacteria; now, it’s
time to learn more about the beneficial fungi in the living soil. So, the
answer to the question “can a fungus be beneficial to growing plants in your
landscape” is yes.
The beneficial soil fungi are called Mycorrhizae, pronounced my - core - rye’
- zee. Scientists have determined that probably more than 98% of all the plants
in the world have a mycorrhizal association. The actual functions of the
mycorrhizae are as follows:
- Aid in the faster absorption of water and nutrients from the soil beyond the normal root zone.
- Help protect the roots from soil pathogens.
- Reduce water and summer heat stress.
- Extend the normal root zone
- Increase tolerance to heavy metals, saline soils, and drought.
- Improve the plant’s tolerance to extremes of soil acidity and alkalinity.
- Improve yields of fruit and vegetable crops
- Help to establish root systems in newly transplanted plants
- Promote more and better root and shoot growth
- Reduce fertilizer requisites by half or more, once established
Can plants survive without mycorrhizae? Yes; nurserymen for the most part
do not inoculate their sterile soils with mycorrhizae and yet they produce
some very nice plants: However, when those nice plants are placed in your
landscape, some decline and die even after our best efforts to keep them
alive. What happened? Since our highly alkaline landscape soils are so
different from the plants’ original soil, they could not adjust. One of
the functions of the mycorrhizae is to improve the plants tolerance to
extremes of soil acidity and alkalinity. You might ask, doesn’t my soil
have mycorrhizae? Well, maybe yes, maybe no. If your house is newly constructed
the answer is no; mycorrhizae are found only in soils where plants have been
established for long periods of time. If your house was built some years ago,
some mycorrhizae have probably moved in, but in many instances it is hit or
miss as to whether or not there are enough mycorrhizae in your soil. Remember, “mother nature” took millions of years to develop the mycorrhizae in natural habitats and your landscape probably does not fit into that time frame.
What are mycorrhizae? The word mycorrhizae is derived from two words
“mycor” which means fungus and “rhizae” which means root. Put the two
parts together and we have “fungus root”. Mycorrhizae form a symbiotic
relationship between the fungus and the root. When the fungus is present
and the symbiotic relationship has been formed, the benefits to the plant
as described above will occur. A recent, as yet unpublished experiment on
Lychees conducted by the University of Florida in Homestead has shown a 26%
increase in growth in inoculated versus non-inoculated, container grown
trees. At the present time research on mycorrhizae is being conducted in
many countries around the world. Just log on to the Internet and do a
mychrrhizae word search and you will be amazed at what turns up.
There are two types of mycorrhizae - ectomycorrhizae and endomycorrhizae.
Ectomycorrhizae colonize the outsides of the root cells and are most
typically found in northern coniferous forest such as pines, firs and spruces,
and hardwood forests such as oak, beech and birch. Here in south Florida oak
and pine are the two most common ectomycorrhizal trees. The fruiting bodies
of these fungi are born above ground in what we know as puffballs or mushrooms
and the spores of the eclomycorrhizae are wind disseminated.
Endomycorrhizae colonize on the inside of the cell walls and spores are
found below ground and not wind disseminated. The most common endomycorrhizae
are vesicular-arbuscular mycorrhizae (VAM), and are associated with mangoes,
citrus, mahogany, avocados, and in general, except for oak and pine trees,
all of the remaining landscape and vegetable plants grown in South Florida
except members of the cabbage family.
Both types of mycorrhizae produce an extensive web-like growth called hyphae
outside of the root. Mycorrhizal fungi develop an immense network of hyphae
that, in effect, serve as extensions of the plant root system. Because the
surface area of the hyphae may be several hundred times the surface area of
the roots, plants have access to a much larger volume of soil, and thus water
and nutrients, than they would through their roots alone. By sending threads
of hyphae far from the normal root zone, mycorrhizal fungi also improve the
soil structure, thus improving the porosity of the soil.
Mycorrhizae, like beneficial soil bacteria, are not a panacea; they only
help “mother nature” do what she does best, i.e. grow better plants. One of
the more interesting facts about inoculating your soil with mycorrhizae is
that it only has to be done once. After the initial inoculation the mycorrhizae
will continue to grow with the root system and in time even inoculate other
So, what can you do to add mycorrhizae to your soil. The process is simple;
at the time of planting just mix the mycorrhizae with the back fill; in the
case of potted plants use a pencil as a dowel to punch 2 to 4 holes, 3 to 4
inches deep in a pot, then add 1 tablespoon of material to each hole. In
existing landscapes, set up a grid 30 inches on center, then with a broom
handle punch holes 10 inches deep, put 1/4 cup of mycorrhizae in each hole
then fill the hole with soil.