Creating the perfect soil for your garden
Evaluating the Soil in your garden
In some gardens the soil is like glue when it's wet and like brick when it's dry. In others you can pour on water until the bill reaches three figures and still find some plants drying up.
But even if that first spadeful of soil looks as if it wouldn't grow weeds, there's no reason to be discouraged. With a little time and effort you can solve almost any soil problem and produce a growing bed that rivals, and often exceeds, the quality of commercial farms.
Read the descriptions of soil types below and compare them with your own soil. If it needs improvement, check over the soil amendment chart and plan accordingly. The important thing to keep in mind is that any soil problem has some kind of solution. After all, you can garden on concrete if you use containers and a good potting mix.
Building good soil
Don't be impatient. It may take several seasons of proper soil preparation and maintenance to achieve a permanent change in soil quality. In the interim, a wise choice of plants, regular watering and fertilizers can give heartening results.
You will begin to see improvements in the growth of your seeds and transplants the first season and an increasing abundance as each year passes. Finally after a while you will have a garden that welcomes anything that you plant there.
Heavy soil is easy to recognize but hard to work with. When it's wet it sticks to your spade. Squeeze a handful together and you'll get a gummy plastic mass that doesn't break apart even if you tap it with your shovel. When heavy soil dries, it tends to crack, and often becomes hard enough to deflect a pick.
Individual particles of clay are very fine. With a microscope you would see them as flat plates. Because of their shape, they pack tightly together. One large particle is just 1/25 the size of the smallest grain of sand. There's no air in soil like this, and drainage is poor. Plant roots will refuse to grow because of the lack of air and often drown because of the lack of drainage.
You can improve heavy soil by adding an organic amendment, such as compost, peat moss, or leaf mold. Mixed in thoroughly, these materials immediately create countless tiny air pockets between the flat plates of clay. As they continue to decay, a material called "humus" forms, preventing the clay particles from packing down again.
The advantage of heavy soil is that the clay particles tend to retain moisture and fertilizer. And if you improve it by adding an amendment, heavy soil pays you back by making every drop of water and every ounce of plant food count.
Sandy soil. At its worst, sandy soil is the exact opposite of clay. No matter how often you wet it, the big rounded particles quickly dry up. There's plenty of air in soil like this, and roots can go where they like. But water pours right through, taking with it any plant food you've added.
Sandy soil can be improved by adding organic amendments. The amendment particles fill the open spaces between sand particles and help to retain water and nutrients. As an amendment decays, however, the resulting humus tends to leach away with each watering. That won't happen right away, but if, after a few seasons, you seem to be watering more than usual, give your soil another application of the organic amendment.
Organic soil amendments
Soil amendments are of two distinctly different types. The first type may be almost anything that comes originally from an animal or plant (bone meal, peat moss, or manure). Some of these amendments are primarily a source of nutrients and are normally used as organic fertilizer. An example is bone meal which is rich in phosphorus.
Others have no nutrients but help fluff up heavy soil and then rot to produce humus (peat moss is of this type). Some contain tiny amounts of plant nutrients (manure is an example) but are used mainly as soil improvers.
Mineral soil amendments
This type of amendment comes in small-chunk form. Added to fine, heavy soil, it stays in place more or less permanently adding texture and tilth. Some examples are sand, perlite, pumice, and vermiculite. Most of these materials are too expensive for large areas but are often used in special soil mixtures for containers or in the home garden.
Qualities of soil amendments
In choosing an amendment, the most important consideration is texture. If possible, choose an amendment that is granular and fine-grained. Granular materials are easier than fibrous materials to mix evenly into the soil. And, in general, even-textured materials amend the soil better than highly variable ones. For example, sawdust that has a high percentage of large shavings and wood chips is less effective than the same kind of sawdust that is composed of tiny particles.
If you live in an area with a normal amount of rainfall, some salt content in soil amendments will cause little if any trouble. But if you live in a region with low rainfall, the salt content is crucial. Manures often contain quantities of salts. Without heavy rains to wash away these salts, you may find that young or sensitive plants begin to show burned leaf edges.
Materials such as sawdust, ground bark, and straw quickly decompose after you mix them with soil. The rotting agents are fungus and bacteria. As they work to break down the amendment, they use up nitrogen. Unless you add nitrogen to the soil along with the conditioner, your plants will not have enough nitrogen for growth. You may use either a chemical fertilizer, such as ammonium nitrate, or an organic fertilizer, such as blood meal. The chemical fertilizers may burn plants when used in large quantities, so the organics are safer as a rule.
If you choose a chemical garden fertilizer, the package label tells you only the percentage of nitrogen it contains, so you'll have to translate the first number on the package of fertilizer into actual pounds of nitrogen. Look for a group of three numbers on the label, something like 10-8-6. From left to right, these numbers give the percentage of nitrogen, phosphorus, and potassium in the material.
The hypothetical 10-8-6 fertilizer contains 10 percent nitrogen compounds, 8 percent of a phosphorus compound, 6 percent of a potassium compound, and 76 percent inert material. If you use raw redwood sawdust you'll need to add 1/3 pound actual nitrogen for each 10 cubic feet of sawdust you add to the soil.
If you have a 25 pound bag of a fertilizer labeled 10-8-6, you would calculate that 10 percent of 25 pounds is 2.5. This means that the bag of fertilizer contains 2.5 pounds of actual nitrogen. Since you need to add 1/3 pound of nitrogen, you will use roughly 1/7 of the fertilizer. You don't have to be absolutely exact. Just visually divide the bag into seven parts and scoop out what you need. If you use blood meal or hoof-and-horn meal no figuring is necessary.
Also an important consideration in choosing an organic amendment is the quantity of ash (mineral matter) it contains. Ash is of questionable value in improving soil. And the higher the percentage, the less efficient the conditioner.
For example, a truckload of fine sawdust may contain from 1/2 to 3 percent ash. A truckload of poor quality manure may contain up to 50 percent ash. Almost every grain of the sawdust is useful as a soil improver, while half the manure is composed of salts, stable dust and dirt, gravel scooped up with the manure, or possibly just earth from the pens.
The professionals use a complicated term - "cation exchange capacity" - when they are talking about whether or not the fertilizers that you add to amended soil are going to stay there. Some materials will hold to nitrogen and other nutrients, whereas others let them slide away.
Wood products are poor at holding nutrients, but that doesn't matter if the soil is heavy, since it's already a good nutrient holder. Because peat moss does the best job of conserving added nutrients, it is ideal for use in containers and sandy soils. Manure actually supplies nutrients on its own and is also good in sandy soil. However, because of its salt content, it should not be used in containers.
How much amendment to add:
When you add an amendment, the final soil mixture should contain at least one quarter amendment and three quarters soil.
But if your soil is almost pure clay or sand, the finished mix should contain about half amendment and half soil.
If your spade or rotary tiller penetrates 9 inches deep (most do), you should apply a 2 to 3-inch layer of amendment over normal soil before tilling the soil. For a half and half mix, you'll need enough material to make a 4 to 5-inch layer.