Healthy Soil
Adapted from Rodale’s All-New Encyclopedia of Organic Gardening, pages 541-550, with permission from Rodale Institute
Healthy soil is the key to successful organic gardening. The basic principle that organic gardeners live by is to feed the soil, and let the soil feed the plants. The challenge for organic gardeners is to balance the soil so that it provides all the conditions plants need to thrive.
You may wonder why the soil in your yard and garden would be out of balance. There are several possible reasons:
- The surface soil around many homes may have been disturbed—and even removed—during construction, and nothing done to restore the soil afterward.
- Driving equipment, such as a lawn tractor, or repeatedly walking on soil compacts it, harming it’s structure.
- Your soil's natural characteristics may not be favorable for gardening. For example, you may have a soil that is so sandy that it does not hold sufficient water and nutrients to support vigorousplant growth, or your soils pH may be so acidic many kinds of plants won't thrive.
- Unless you're a longtime organic gardener, the soil may be depleted by years of cropping without replenishing organic matter, the soils natural storehouse of nutrients.
- If you've used chemical fertilizers, the soil microorganisms that play an important role in maintaining natural fertility may have died off.
The first step in the process of improving your soil organically is to learn about its characteristics. There are many tests that will help you analyze your soil. After testing, you'll know what problems your soil has, and you can take steps to remedy them. Your soil improvement process will include adding organic matter and other soil amendments. While you work on improving your soil, you may want to use organic fertilizers to boost plant performance.
Investigating your soil
One question home gardeners frequently ask is, “Should I be adding anything to the soil this spring?” The best way to answer that question is to investigate your soil—to learn about its structure and content by observing and testing.
There are several simple soil tests you can do yourself to learn about your soil structure, drainage and earthworm activity (earthworms are a key indicator of soil health). You can also submit soil samples from your yard for soil analysis. When you want to know about the nutrient content of your garden soil, Burpee’s Deluxe Garden Soil Testing Kit is easy to use and provides you with everything you need to perform 15 tests each for available nitrogen, phosphorus and potassium, and 30 tests for soil pH. The handy, battery-free Electronic Soil Tester gives you instant readings on fertility and pH during the growing season.
Preparing a Soil Sample
You may want to collect many samples from around your yard and combine them to submit for a single test and report. Or you may want to prepare separate samples from your vegetable garden soil, your lawn, and an area where you hope to create a flower border, for example. However you'll have to pay three times as much to get these separate tests of recommendations.
Follow these steps to prepare a sample that will accurately reflect the content of your soil:
- Scrape away any surface litter or plant growth from a small area of soil. Use a soil probe to cut a core of soil, or dig a hole with a stainless steel trowel or other tool (if you don't have stainless steel tools, use a large stainless steel spoon) and collect a slice of soil from the side of the hole. For cultivated areas, collect a core or slice to a depth of 6 inches. For lawns, collect your samples only from the top 4 inches of soil.
- Repeat the sampling procedure at 10 to 15 different locations around your yard or the particular area you are sampling.
- Mix the soil cores or slices in a clean plastic or stainless steel container.
- Place some of the mixed sample in a plastic container or bag, and put it in the bag supplied by your Cooperative Extension service or the soil testing laboratory for shipment.
Don't touch the sample with soft steel, galvanized or brass tools or with your bare skin. The content of some minerals in soil is so small that minerals picked up from these metals or your skin could throw off test result.
You'll send your sample, along with an information sheet concerning your soil's history and your future gardening plans, to the testing laboratory by mail. Be sure to write on the information form that you want recommendations for organic soil amendments.
Improving Your Soil
Now that you’ve tested your soil, you’re ready to take action. There are no overnight or even single-season organic solutions for an imbalanced soil. Unlike gardeners who rely on soluble synthetic chemical fertilizers to keep their plants green and growing, organic gardeners boost the soil’s natural fertility through a two-, three-, or four-year program that results in a fertile, rich soil. However, your plants don’t have to suffer during the soil-building years. You can supplement your soil building program with organic fertilizers to meet your plants’ needs for nutrients.
Phosphorus is critical for root growth early in the season and flowering and fruiting later. If your soil test shows low levels of phosphorus, bone meal is an easy-to-apply organic solution. It comes with calcium, which plants need to build new cells and other functions.
Plants need a steady supply of nitrogen, the nutrient that fuels leaf and stem growth. Instead of fertilizers made with synthetic sources of nitrogen, organic gardeners rely on natural soil amendments such as blood meal. In addition to powering plant growth, blood meal nurtures the soil food web.
Did your test say your is too acidic? An application of garden lime will help bring it to the optimal level of about 6.0 to 6.5.
Many experienced organic gardeners today are adding biochar to their garden soil mix. It’s a by-product of burning wood and plant debris in sustainably managed forests. It helps soil retain moisture and activates the microorganisms that plants depend on.
Adding Organic Matter
The single most important step you can take to improve your soil is to increase its organic matter content. Adding organic matter will help improve your soil’s structure and biological activity. Organic material stimulates the growth and reproductive capacity of the bacteria and other micro-organisms that help create a vital and productive soil. Adding finished compost or other partially decayed organic material can also go a long way toward helping solve mineral deficiencies in your soil and can even modify soil pH.
There is a wide range of organic materials available to gardeners. The best of these is compost - a mixture of decayed organic materials. Other good organic materials include:
- Aged manure
- Chopped leaves
- Straw
- Grass clippings
- Peat moss
Adding Microbes
If you’re a gardener who’s switching to organic methods from chemical methods, or if you’ve inherited a garden that’s been treated with pesticides, you may have soils with very low biological activity. Give some extra help to the struggling microbial populations by applying bacterial cultures that give your soil and compost piles a biological boost. Some of these cultures are in a dry, dormant, powdered form. After you spread this material over your soil or into a compost pile, the microbes become activated and biological activity accelerates. Keep in mind that you must keep adding sufficient organic matter to feed the increased populations of soil microbes, or you won’t get any lasting benefit from your investment.
If your earthworm count is low, don’t despair. Once you provide more organic material to feed them, they will usually return. Earthworm egg casings can lay dormant as deep as 20’ in the soil for as long as 20 years.
Dry or granular, fast-acting chemical fertilizers can repel earthworms when they dissolve in water and leach down into the soil. Earthworms are highly sensitive to changes in the physical and chemical environment and will avoid the salty conditions created by the chemical fertilizers. If you are making the transition from chemical fertilizers to organic soil amendments and fertilizers, have patience. As your soil reaches a healthy balance, you will see more earthworm activity.
Adding Minerals
There are several organic soil amendments you can add to correct specific pH and mineral imbalances. In most cases, you should only add these amendments according to recommendations from soil tests or plant analyses. If you add too much of a natural mineral supplement such as rock phosphate, you can create an excess of a particular nutrient. The excess may damage plants or may interfere with uptake of some other nutrients. For more information on soil amendments, see the Fertilizers entry.
Adapted from Rodale’s All-New Encyclopedia of Organic Gardening (2009), with permission from our friends at Rodale Institute, a nonprofit dedicated to growing the regenerative organic agriculture movement through rigorous research, farmer training, and education. Burpee has been a longtime partner of Rodale Institute and supports its mission to grow organic agriculture in the U.S. with an annual scholarship for a student in the Regenerative Intensive Farmer Training program.