The condition of your garden soil can make or break the productivity of the garden. Yet, what most people see when they look at their soil is a lot of dirt. It’s the stuff that comes into the house on our clothes, shoes, fingernails, and dogs. However, soil is much more than that.
What gardener doesn’t dream about having perfect soil–crumbly, well-aerated, sweet-smelling, stuff that would grow 10-foot-high corn, elephant-size watermelons, and even lip-smacking tomatoes? Technically, the perfect garden soil contains 50 percent solid matter and 50 percent “pore” space (the space that allows absorption of liquid). Moisture occupies about half the pore spaces, soil air the other half. Of the solid matter, roughly 45 percent should be mineral matter, 5 percent organic. The water in this soil carries the dissolved nutrients easily to plants’ roots, and the air in the soil provides a constant supply of oxygen while at the same time carrying off carbon dioxide. It also contains all the nutrients necessary to make your plants healthy.
Know Your Soil
Most garden soils are far from perfect, yet many gardeners plant without making any improvements and then wonder why their vegetables are far from ideal. Most backyard soils are going to need a little help. If you look in your own garden, you’re likely to find clay, sand, and silt.
Clay soil is composed of fine, flat, wafer-like particles that fit together tightly and take in water slowly. Chemically, clay is chiefly silicon and aluminum, with small amounts of sodium, magnesium, iron, calcium, and potassium. When you sprinkle a clay bed, the water runs off instead of sinking in. If the clay particles do absorb moisture, they hold it too tightly for the plants to use much of it. When it’s rubbed between the fingers, wet clay soil feels smooth, soft, and slippery.
When clay dries, it often has the consistency of brick (and yes, I’ve made adobe bricks from this stuff). The particles are so compressed that there isn’t any space for air to penetrate, and plant roots have great difficulty forcing their way down. Plants grown in untreated clay soil are often stunted and have pale green or yellow leaves.
Sandy Soil is at the opposite end of the scale. It is lighter than clay but has particles 25 times larger. While sand is easy to dig in, it has almost no capacity to store water, which moves freely through the soil and quickly leaches out the nutrients. Sandy soils warm up faster than clay soils and reflect a considerable amount of heat. Most sandy soils, however, contain enough clay and silt to retain some water and nutrients.
Sandy soil rubbed between the fingers feels grainy and gritty; gravelly soils are self-evident. Plants grown in sandy or gravelly soils frequently have yellow or pale green leaves.
Silt falls somewhere between clay and sand. It consists of medium-size gritty particles that pack down hard almost like clay and is seldom very fertile. If a silt topsoil covers a layer of heavy clay, the plants may be stunted because the clay layer traps and holds water. Silty soil rubbed between the fingers feels slippery but has a grainy texture. Plants grown in silty soils often have pale green or yellow leaves.
Loam is the kind of soil every gardener wants, and although it isn’t the theoretical ideal described earlier, it’s close enough to grow great vegetables. Loam is crumbly granular soil that has close to even quantities of different-size particles and a good supply of humus (decomposed organic material). A combination of root growth, worms, and bacteria gives this soil’s grains a good structure, enabling both adequate retention of water and proper drainage. Similarly, air moves freely through this soil, so roots can find their proper depth. Technically, the U.S. Department of Agriculture considers loam to consist of 7 to 27 percent clay, 28 to 50 percent silt, and 20 to 45 percent sand. Plants grown in loam are usually vigorous, healthy, and green.
Improving Soil Structure
You can improve clay, silty, and sandy soils by adding massive amounts of organic material. Shovel 6-8 inches of compost, ground bark, sawdust, leaf mold, manure, or peat moss over the top of the garden area (adding nutrients according to the formulas listed below) and then spade or rototill this layer into the soil.
Organic particles in clay soil hold the compacted clay particles apart while acting as a kind of glue to hold the fine clay particles together in crumbs. This opens up the soil and allows air and water to circulate freely, which gives vegetables a fighting chance.
Adding fine-textured organic material to sandy soil fills the spaces among the grains and helps retain water both by stopping the flow and by absorbing some of it.
If you decide to go the raised-bed route, plant your garden in a bed that’s 8-12 inches high and filled with equal parts loam, sand, and organic material (compost, rotted manure, and similar matter). These raised beds provide beneficial drainage, give the roots a good growing medium, and warm up faster in the spring than regular garden beds.
You can buy a good organic fertilizer from a nursery or order one from the sources listed below. You can also mix a worthy organic fertilizer yourself. Here are three formulas.
Formula One Formula Two Formula Three
2 pints blood meal 4 pints cottonseed meal 2 pints blood meal
4 pints bonemeal 3 pints bonemeal 4 pints bonemeal
3 pints greensand 3 pints greensand 2 pints wood ashes
For the average garden, use 1 1/2 gallons per 100 square feet.
Vegetables generally need 15 nutrients for maximum growth. Three elements–oxygen, carbon, and hydrogen–dome from air and water. The other 12 exist in the soil. Nitrogen, phosphorus, and potassium are the major macronutrients needed by vegetables in large amounts.
Nitrogen, produces leaf growth and gives leaves a vibrant dark green color. It helps generate a healthy root system, increases the set of fruit, and nourishes soil microorganisms. It is especially import for such leafy vegetables as lettuce, spinach, cabbage and collards. Nitrogen deficiency causes yellow leaves and stunted growth. Excess nitrogen delays flowering, produces excessive growth, reduces the quality of fruits, and renders crops less resistant to disease.
Phosphorus stimulates early root formation, hastens maturity, and is important for the development of fruit, flowers, and seeds; it also helps provide disease resistance and winterkill protection. A phosphorus deficiency causes dark or bluish green leaves followed by bronzing, reddening, or purpling, especially along veins and margins. Lower leaves are sometimes yellow, drying to greenish brown or black. Plants are often stunted, spindly, late to mature. Excess phosphorus produces iron and zinc deficiencies in corn, beans, tomatoes, and other plants.
Potash (potassium) is important in plants’ ability to manufacture sugar and starches. It improved the color of flowers and the length of time fruit is edible. It promotes vigorous root systems and is essential in growing good root crops. It produces strong stems, reduces water loss, increases vigor, combats disease and reduces winterkill. Potash deficiency causes dry or scorched leaves, and there may be small dead areas along the margins and between the leaf veins. Plants are sometimes stunted and appear rusty while their fruit is often small and thin-skinned. Excess potash produces coarse, poorly colored fruit.
Magnesium is important in chlorophyll production. It promotes early and uniform maturity and is important in fruit growth. Magnesium deficiency causes yellowing of the lower leaves at the margin, tips, and between the veins. The leaves wilt from the bottom up until only the top leaves appear normal. Magnesium deficiency in corn shows up on the leaves as yellow stripes. Excess magnesium may produce a calcium deficiency.
Manganese is important for green plant development. It is essential to both respiration and normal chlorophyll formation. Manganese deficiency causes stunted growth and mottled yellowing of lower leaves. Excess manganese may produce small dead areas in the leaves with yellow borders around them.
Copper is an enzyme activator and plays vital roles in both chlorophyll and protein formation. Copper deficiency produces dark green, grayish-olive, or blue leaf edges that curl upward. Flowering and fruit development is checked, while carrots are poorly colored and bitter. Excess copper stunts roots and prevents the uptake of iron.
Zinc is another enzyme activator and is necessary for normal chlorophyll production and cell division. Zinc deficiency brings about mottling, yellowing, or scorching of the tissues between veins.
Iron promotes chlorophyll production. Insufficient iron causes mottling, yellowing, or scorching of the tissues between veins.
Sulfur helps maintain the dark green color of plants. It is also a constituent of proteins and growth-regulating hormones. If soil doesn’t have enough sulfur, young leaves turn pale green or yellow while the older leaves remain green (yellowing in nitrogen-deficient plants start with the older leaves). Plants become dwarfed and spindly.
Calcium promotes early root formation, improves general vigor, and increases resistance to disease. Calcium deficiency causes distortion in young stems, and stem tips die. Excess calcium can cause a deficiency (reduced intake) of potassium and magnesium..
Molybdenum form chlorophyll and sugar, which is important for seed development and required by the nitrogen metabolism of all plants, although only in minute quantities. Insufficient molybdenum leads to stunted, crinkled leaves that are pale green or yellow and malformed.
Boron influences the conversion of nitrogen and sugars into more complex substances. A deficient amount of born is shown in the scorching of tips and margins of younger leaves. Excess born turns leaves yellowish red.
The availability of all nutrients needed for plant growth also depends on the soil’s pH, so keep that in mind when you consider the possible causes of a problem.
Where to Find Natural/Organic Fertilizers
Catalog Code Seed Catalog Web Address
ABU Abundant Life Seeds www.AbundantLifeSeeds.com
BOU Bountiful Gardens www.bountifulgardens.org
BURP Burpee www.burpee.com
COO The Cook’s Garden www.cooksgarden.com
HAR Harris Seeds www.harrisseeds.com
NIC Nichols Garden Nursery www.nicholsgardennursery.com
PAR Park Seed www.parkseed.comPEA Peaceful Valley www.GrowOrganic.com
PLA Planet Natural www.planetnatural.com
SHU R.H. Shumway www.rhshumway.com
TER Territorial Seed Co. www.territorialseed.com
TOT Totally Tomatoes www.totallytomato.com
VER Vermont Bean Company www.vermontbean.com
Peaceful Valley Farm & Garden supply www.GrowOrganic.com
WEB ONLY Dirt Works www.dirtworks.net
Soil, Alkaline or Acid?
Soil scientists express acid (sour soil) or alkaline (sweet soil) using a scale of 1-14 that represents hydrogen-ion concentration, or pH. It’s actually simple: 7 is neutral; below 7 is acid; above 7 is alkaline.
Vegetables are finicky. Each type has its own particular pH requirements, (see individual vegetables). Since it isn’t practical to make one planting section your garden one pH and another section a different pH, most gardeners compromise on a slightly acid to neutral soil (pH 6.5-7).
Testing pH is a simple task. A pH test kit works just fine. A battery operated pH meter automatically registers the pH when its prongs are placed in the soil, but is more expensive. If you need to make a number of pH tests on a continuing basis, a pH meter is the most convenient device. If you’ll be making only a few tests in a small plot, a pH test kit will do the job.
If your soil is too alkaline, your plants may show yellow leaves, stunted growth, and leaf margins that appear burnt. Alkaline soils are sometimes too salty, and in extreme cases, heavy brown or white salt deposits are left on the soil surface. Acid soil is not easy to detect visually and will generally require some sort of pH test. This often occurs in areas of low rainfall and poor drainage, as well as in regions where there are natural limestone deposits. The soil in the Southwest tends to be alkaline.
Soils turn acid when calcium and magnesium ions are leached out and replaced by hydrogen ions. This occurs frequently in areas of heavy rainfall. The Northeast tends to be slightly acid.
To counteract acidity, add ground or dolomitic lime at the rate of about 4 pounds per 100 square feet for each unit of pH below 6.5. To correct alkaline soil, add sulfur at the rate of about 4 pounds per 100 square feet for each unit of pH above 7.
When you create the right soil conditions at the start and infuse the soil with nutritional supplements each growing season, you wind up with a soil that will continually grow sound, healthy vegetables with only a minimum of additional effort.
Light Feeders Heavy Feeders Soil Restorers
beets broccoli beans
carrots Brussels sprouts peas
New Zealand spinach