Most people are aware of the large critters that move through our soils such as moles, gophers, beetles, earthworms, etc., however, they may not be aware that there are about one billion “critters” in each gram of soil, which equates to about a good pinch of soil These “critters” are bacteria, actinomycetes, fungi, yeasts, protozoa, viruses, algae, and nematodes They are microscopic organisms that live in the soil, and we exist today because of them They give soil life, which is necessary to grow plants; the backbone of our existence.

Each microorganism has a unique function and they exist in most soils For sterile soils, or ones with low activity, you can actually replenish these critters, but it is not cheap, and they will reproduce naturally in the right conditions, which will be discussed later in this article.

Bacteria are the most common microorganism in soil, are found in the top foot or so of soil, and survive most conditions Of all microorganisms, bacteria comprise about 70 percent of the total; there are approximately 3 to 20 million bacteria in a gram of soil Bacteria are important because they feed on organic matter, help with decomposition to return nutrients to the soil, assist in the reactions of materials which will make them available to the plant, especially nitrogen, and fix nitrogen from the air Without bacteria, plants could not absorb nitrogen, and therefore, will not survive Most of these bacteria are harmless to man Tetanus is one of the more harmful bacteria in the soil and causes lockjaw, a nearly fatal disease Thus, it is important for all gardeners to have their tetanus immunizations and have them updated every ten years Anthrax and Botulism are two other bad actors that live in the soil.

Most bacteria are aerobic (needs oxygen) to function If the soil contains less than one percent oxygen, then it because anaerobic (without oxygen) When this happens, the “good” bacteria will give way to the bad or offensive bacteria that thrive in anaerobic conditions, such as riverbed silt.

Actinomycetes are rod shaped bacteria that are saprophytes, those that live off, or gain nutrients from decaying matter The antibiotic Actinomycin is obtained from these soil bacteria There are about 1 to 20 million actinomycetes per gram of soil, which makes up about 13 percent of the total soil organisms Their main function is to help with the decomposition process, and during the process, liberates carbon, nitrogen and ammonia, and helps form humus They are very effective in breaking down cellulose.

Fungus is definitely among us Fungi can be found in the air, water, plants, and soil Fungus helps break down organic matter There are about 5,000 to 1 million fungi per gram of soil, which is about 3 percent of the total organisms in soil The most important fungi are the mycorrhizals These fungus collect on the roots of the plants and form a symbiosis relationship with the plant, where they “live” off each other without harm to either host The fungus lives off nutrients from the plant, and provides greater surface area on the roots for the plant to absorb water, air, and nutrients You can purchase mycorrhizals for poor soils, however, it is not cheap and they will form naturally Some fungi are visible to the eye If you pick up an old, rotting piece of wood and notice strands of white fiber like material, that is one of the fungi There are some hazardous soil fungi which includes the agent for the “Mummy’s Curse” and Valley Fever (Coccidioides immits).

Yeasts are present in minor amounts in the soil, from 1,000 to 1 million per gram of soil They are generally found around the plant root areas Their actual function is unknown, but it is believed they help decompose organic materials.

Protozoa are the regulators (predators) of algae, bacteria and fungi populations They are present in the top few inches of soil and there are <1/2 million of them per gram of soil.

Algae are multicelled microorganisms that live in the top few inches of the soil They assist in nitrogen fixation from the air and produce plant growth stimulating compounds There are 100 to 50,000 algae in a gram of soil.

Viruses and prions are present in soils in very small amounts They are more destructive than beneficial, but are not major problems.

Nematodes are basically small worms Some are good and others bad In Florida, a type of nematode invades rose plants; therefore roses are grafted onto Fortuniana rootstock which is resistant to nematodes However, most soils have good nematodes They also assist in the breakdown of organic material and they help keep down populations of grubs and termites There are 10 to 5,000 nematodes per gram of soil

The ideal soil should contain about 5 percent or more of organic matter  The importance of organic matter is to increase soil organisms, thus making soil more plant friendly, which will help grow better roses With low organic matter soils, bacteria and earthworm activities are poor, and with that, the plant will not have enough nutrients available for growth

If the soil has a low organic matter composition, add more humus, compost, manures, etc., to the top 4-6 inches of the soil To go from a 2 percent to 5 percent organic mixture in your soil, you need to add about 2,000 pounds of organic material per 1,000 square feet and work it into the top 4-6 inches of the soil 2,000 pounds of compost is about 2 cubic yards, which is about two skip loader scoops from your local soil company.

Adding organic material to the soil will increase soil pH, in other words, make the soil more acidic This is good for areas that are alkaline (basic) Microorganisms are affected by pH, so it is important to make sure the pH is in the proper range To find out how much organic material is in your soil, do a simple soil test Scrape off your mulch cover and take soil samples from different parts of your rose bed Take a small handful and place in a large jar with a lid Add water to about 3/4 full, and shake vigorously The soil particles will drop out depending on the size; rocks, then sand, then silt, then clay, then organic material The organic material may also float This test will approximate the organic matter is in your soil The best soil test is to send a sample to a laboratory for full analysis A full test will tell you everything about your soil including levels of nutrients and pH Most labs will analyze it for ideal rose growing and tell you how much, if anything, needs to be added to your soil A full analysis will run around $25 per sample It is worth the price.

With the high use of fumigants, chemical fertilizers, insecticides, and fungicides, the amount of soil critters will decline, and plants will suffer So make sure your soil is alive with these “critters” so you will have healthy soil, which will grow healthy plants