January 2, 2015
Carrots in Soil. Photo by Katie Harris, Full Earth Farm
By Molly Jameson
Whether you are ready to start your very first garden or want to revitalize your existing garden, the important thing to remember is that a healthy garden requires life. But what is it that separates a thriving, healthy garden that can support fruit and vegetable production from one that cannot? The answer is in the soil. As soil transitions from being impoverished to being enriched, many living entities will form very complex ecosystems that occur right beneath our feet.
Just a teaspoon of healthy topsoil can contain up to one billion bacteria and numerous other microorganisms such as fungi, protozoa, and nematodes. So how can you as a gardener attain these microorganisms in your own garden space? The answer is organic matter. Organic matter is mostly composed of decaying plants, animals, and soil microorganisms. Less than 5 percent of organic matter is actually living organisms, yet without this fraction, the organic matter could not exist.
Microorganisms will improve your garden by providing soil structure, aeration, and the conversion of fertilizer into soluble, plant-available forms. When soil microorganisms decompose organic matter, they create groups of soil particles that are bound together. These are known as soil aggregates. Aggregates reduce soil compaction and greatly increase porosity for strong root growth and improved drainage. It is not until the organic matter is decomposed by microorganisms that it provides all of these essential benefits to soil for a productive garden.
The portion of organic matter known as humus (pronounced “hume”-us) is very beneficial to gardeners. Humus decomposes very slowly, and is comprised of many complex organic compounds, including lignin, protein, and sugars that enhance soil’s physical and chemical properties. Humus is the glue that binds the small soil aggregates, providing micro, meso, and macro (tiny, small, and large) pore space for improved infiltration, but also enhanced soil water retention. Humus will provide a slow-release nutrient source, as it has a very large surface area capable of retaining many essential nutrients imperative for plant development. Humus acts as a soil buffer, which maintains proper soil pH, and can also bind heavy metals which otherwise may cause plant metal toxicities.
Microorganisms such as rhizobia bacteria and mycorrhizae fungi provide direct benefits to your garden by forming symbiotic relationships with legumes – such as beans and peas – for atmospheric nitrogen fixation. This essentially provides free fertilizer to your garden, so be sure to include legumes within your crop rotation. Soil also provides an excellent habitat for nematodes, which are microscopic roundworms. Although the plant-parasitic types give nematodes a bad reputation, most soil nematodes are free-living and can be very beneficial for their ability to decompose organic matter.
A quick test to see whether your soil could use more life is to pick up a handful of topsoil and gently squeeze it in your palm. If the soil particles easily fall apart and quickly fall through your fingers, it probably means your soil is predominately sandy in texture and you may lack a healthy population of soil microorganisms. Not to worry – adding compost and organic mulch (grass clippings, chopped leaves, pine needles, etc.) can do wonders to encourage a favorable environment for life. It is also important to keep your soil moist (but not soggy), as all life requires water. Also remember to keep your soil aerated, as most good bacteria are aerobic and therefore require oxygen. Many pesticide applications can negatively affect diverse microorganism populations, and should generally be avoided. Although plastic mulch can be useful for growing some crops, avoid excessive use, as it can reduce air flow and can disturb the formation of organic matter.
The key to a healthy living soil is maintaining all of the components that life requires. Food, water, and air will mean diversity in your garden. A complex food web will help you combat any unwanted garden pests, securing the health of your soil and the health of the many fruits and vegetables your garden grows for years to come.
Molly Jameson is an Extension Agent with Leon County/University of Florida IFAS Extension. For gardening questions, email us at Ask-A-Mastergardener@leoncountyfl.gov