High Elevation Gardening Web Log "Blog"

Most native plant species have the advantage of drought adaptation, thus they require less care
and less water than non-native species. However, prior to purchasing seed, you should check the habitat requirements for the mature plants and make sure that you can provide those needs.

Once you have chosen which plants you wish to grow, you will need to provide three basic needs to the growing plant: Sunlight, water and soil. The soil is by far the most complex of the three basic needs and it can be crucial in determining propagation success. In addition to the basic plant nutrients (nitrogen, phosphorus and potassium), the soil also contains a host of microorganisms that play an important role in plant growth. Probably the most important of these organisms is a group of fungi known as mycorrhizal fungi. The term mycorrhiza literally means "fungus-root." These organisms form symbiotic associations with plant roots that are
generally beneficial. The fungus provides the plant with improved water and nutrient uptake, while the plant provides the fungus with a source of food (photosynthate). Additionally, mycorrhizal fungi can also provide their host plant with improved drought tolerance, protection from soil-borne pathogens and protection from certain herbivores. The benefits provided to the plant by the fungi are particularly important in dry soils with low fertility, like those found in much of northern Arizona. As an added bonus, they are completely natural.

You may be wondering at this point which plant species form these amazing partnerships, and the answer is nearly all of them. Approximately 95 percent of all known plant species form mycorrhizal relationships. There are two main types of mycorrhizal fungi. The arbuscular mycorrhizas associate mainly with herbaceous species (herbs, grasses and forbs). Arbuscular mycorrhizal fungi form structures for the "exchange of goods" inside of the plant roots and these structures can not be seen with the naked eye. The ectomycorrhizas make up the second main group and they associate primarily with woody plant species (trees and shrubs). Ectomycorrhizal fungi form little fungal "socks," also known as fungal mantles, on the outside of the root tip and these can be seen by the naked eye.

Adding a source of mycorrhizal inoculum to your potting soil will provide many benefits to your growing plants and is easily done by mixing a portion of native soil to your potting mix. Because fungal spores are very small, it takes very little native soil to provide your seedlings with what they need. Collect enough native soil to fill your container approximately 1/6 full and mix this with enough potting soil to fill the remaining space. Native soil should be collected from the top 8 inches of soil, preferably from below a healthy specimen from a site where your plants are natively found. For example, if you choose to grow pinyon pine, you would want to collect soil from beneath a healthy pinyon in a pinyon-juniper woodland. If you are unable to obtain native pinyon soil, then using soil from beneath another pine species (e.g., ponderosa pine) will also be helpful. And, as a last resort if you can not obtain any local live soil (because the ground is frozen), then you can purchase mycorrhizal inoculum from certain garden stores or on the World Wide Web. Commercially available mycorrhizal inoculum contains very common species of arbuscular or ectomycorrhizal fungi or both, depending on the type you purchase.

Although this source of mycorrhizal fungi will not be as appropriate as native fungi, the
commercially available inoculum will still provide your growing plants with many benefits and this is a better option than having no mycorrhizal fungi at all.

The application and use of soil microorganisms, specifically mycorrhizal fungi, in improving
propagation and out-planting success is on the rise. This practice has been found to significantly reduce seedling mortality in the greenhouse as well as mortality upon out-planting. For those of you in disbelief, try growing some seeds with native soil (with mycorrhizal fungi) and some seeds in sterile potting soil (without mycorrhizal fungi) and observe the results for yourself. For more information on where you can acquire mycorrhizal fungal inoculum and on how to determine what type of mycorrhizas your plants form, please contact Kris Haskins at the Arboretum at Flagstaff. 774-1442, ext. 114.

The author is a research scientist at the Arboretum at Flagstaff. For more information
about the Master Gardener Program, call 774-1868, Ext. 17 or visit our Web site: highelevationgardening.arizona.edu.