Soil Critters
Bringing the Earth to Life

By Steve Jones
Master Rosarian

Most people are not aware that there are literally millions of "critters" in each gram of soil, which equates to about a good pinch of soil. These "critters" are bacteria, actinomycetes, fungi, yeasts, protozoa, algae, and nematodes. They are microscopic organisms that live in the soil. It sounds terrible, but we exist today because of them. They are what give the soil life, which is necessary to grow plants, the backbone of our existence.

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

Bacteria are the most common microorganism. They are found in the top foot or so of soil, and survive most conditions. Of all micro-organisms, bacteria comprise about 70 percent of the total. There are approximately 3 to 20 million bacteria in that 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 humans.

Actinomycetes are rod-shaped bacteria that are saprophytes, those who 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 in the process, liberate carbon, nitrogen and ammonia, and help form humus.

Fungus is among us. It is true, in the air, water, plants, and in the soil.  Fungus helps break down organic matter. There are between 5,000 to one million fungi per gram of soil which is about 3 percent of the total organisms in soil. The most important fungi are the mycorrhizae. These fungi 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 in the plant, and provides greater surface area for the plant to absorb water, air, and nutrients. You can purchase mycorrhizae for poor soils, however, it is not cheap and they will form naturally.  

Yeasts are present in minor amounts in the soil, from 1,000 to one million per gram of soil. They are generally found around the plant root areas. Their actual function is unknown.

Protozoa are the regulators of the bacteria population. They are present in all soils and there are less than 1/2 million of them in most soils.

Algae are present in about the same levels as the protozoa. They are generally in the top portions of the soil and assist in fixation of nitrogen in the air.  

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, and 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 you have a low organic matter composition, add more compost 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 compost 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 tractor scoops from a local soil company.

When you add more organic material to the soil, you will also raise the pH of the soil, in other words, more acidic. This is good for our area since we tend to have slightly basic soil. To find out what you have in your soil, do a soil test. The first is pretty easy. 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. You can get an approximate idea of how much organic matter is in your soil. 

The best test is to send a soil sample to a lab for full analysis. A full test will tell you everything about your rose garden soil including levels of nutrients and pH. Most labs will analyze it for rose growing and tell you how much of what to add to your soil, if necessary.  A full analysis will run around $25 per sample. It is worth the price.

© Copyright Steve Jones. All rights reserved.

This article is an ARS Award of Merit Winner, originally published in "Rose Ecstasy," bulletin of Santa Clarita Valley Rose Society, Kitty Belendez, Editor.

Photos © Copyright by Kitty Belendez

For questions about Santa Clarita Valley Rose Society, contact:
Kitty Belendez


Updated January 4, 2016