How garden soil is formed
When limestone disintegrates it forms an alkaline or clay soil, composed of very fine particles that tend to cling together, making drainage bad and cultivation difficult. If it is treated properly by frequent cultivation and the addition of humus (organic content) and sand, it becomes one of the best types of soil, because it will retain moisture.
On the other hand, when soil is formed by the disintegration of sandstone or granite, a coarse, sandy, acid soil results, and unless it is treated correctly it may be arid, retaining moisture poorly. The addition of rotted, materials and lime or clay mixed with sod will be helpful.
Soils carried by winds or water, as in glaciers or rivers, and usually found in deltas and lake regions are called transported soils. They differ widely in types and usually are rich. Soil which is formed by the disintegration of rocks and which remains at the place of disintegration is called sedimentary soil. Soils formed chiefly by the decomposition of vegetable matter, as in low or swampy areas, usually are too acid for the growth of many flowers and vegetables and must be drained thoroughly and dressed with lime to neutralize the acidity.
The depth of soils varies greatly in various localities. It may be just a skim, only a few inches, in rocky areas, or it may be several feet, as in lake areas or river lowlands, such as the Mississippi delta.
The average plant grows in the top layer of soil, the roots spreading laterally in quest of food and moisture. The subsoil, or layer below the topsoil, generally is poor in fertility and in ready, usable ingredients for plant growth. If, however, the subsoil is mixed with topsoil, laced with organic matter, and turned up to the sun and the other elements, it soon becomes a part of the topsoil and supports plant life.
A fertile soil must contain organic life ranging from one-celled microscopic animals to worms, organic material upon which the living organisms feed and which they digest and break down for plant assimilation, porosity for aeration and drainage, and a degree of absorbing substance to help retain moisture.
Even an inexperienced planter can tell a good garden soil-if there is a luxuriant growth throughout the season the soil is usually good, with proper drainage and sufficient moisture-retaining qualities. This may be a helpful guide in the selection of property as a site for a home and garden. The presence of garden worms is always an excellent indication of good, loose garden loam; worms would not be present in a heavy, water-logged soil for they would drown.
Here are some helpful hints as to the qualities of soil: If the soil is wet and cold and plants are slow to start, drainage is needed. If the soil is sticky and tends to cling together, some sand should be added. If it is sandy, the addition of humus and leaf mold will help.
Testing soil acidity
It is a very sound practice to have the soil of the garden site tested. A gardener may obtain a thorough analysis by sending samples to the state agricultural station or the county agricultural agent. Do not send soil samples to the United States Department of Agriculture. To take a sample, drive a 2-inch pipe into the ground to the depth of the topsoil and knock the dirt thus gathered onto a piece of paper. Take a half dozen samples from different areas of the garden, mix them together, let them dry, and pack them in a jar. Attach a label on which is stated how the soil has been used and to what purpose it is to be put, and ask for recommendations as to treatment and handling.
The gardener may obtain a simple test for acidity with strips of litmus paper bought at a drug store., Litmus papers are red and blue. Put strips against wet samples of soil for a few minutes. If the blue paper turns red, the soil is acid. If the red paper turns blue, the soil is alkaline. If both turn purple, it is neutral. The degree of acidity may be judged by the speed with which the papers change colorsthe faster the change the greater the acidity.
The gardener may also use a soil testing set; inexpensive ones can be bought at most seed stores.
Most plants flourish in soils that are neutral or almost neutral; some thrive only in strongly acid soils, some only in strongly alkaline soils. In general, shaded soils are likely to be on the acid side as compared to soils exposed to the sun. Soils in woods are always more or less on the acid side because of the excess shade and the accumulated humus from decaying leaves.
Acidity is stated in pH numbers. The symbol "pH7" indicates neutral soil. Numbers, above 7 indicate alkalinity; numbers below 7 show acidity.
Soils generally are acid in the eastern section of the United States, but the pH readings vary widely. They generally are slightly alkaline in the Great Plains, neutral east of the Missouri River, and acid as the Mississippi River is approached. In the Rocky Mountains soils chiefly are alkaline but vary greatly, even within short distances. West of the Cascade Mountains and the Sierra Nevadas soils principally are acid.
The acidity of soils may be changed to meet the requirements of the plants. For instance, lime is one of the oldest promoters of alkalinity. Aluminum sulphate makes for greater acidity. If, however, acid soil is required, most plants will fare better if acidity is achieved by the use of a mulch.
Mulching is an important factor in any gardening operation. Formerly a mulch was regarded simply as a coating of leaves, straw, or well-rotted manure to keep the moisture in the soil; but gardeners today find that it offers many other benefits.
Actually the mere loosening of the soil with a rake or similar tool creates a mulch. While this removes weeds and grasses that are troublesome and unsightly in a garden, it may have the disadvantage of stimulating evaporation in hot, dry spells. A loose, organic mulch is preferred where practical.
A protective winter mulch requires a much heavier blanket of manure or other organic material. This keeps the plants from freezing and from dying of cold, and also prevents them from being heaved out of the soil when it contracts and expands as it freezes, then thaws. The winter rains and snows rot the organic matter and break down the plant material which it contains, letting it pass into the soil to be stored up as nourishment when the plants begin to grow in the spring.
A good substitute for the organic mulch as a protective cover is glass wool or rock wool, house wall insulation material, which is also very useful in blanketing small evergreens and tender upright plants against winter weather. Simply wrap the material around the plants and tie it in place with a cord. It should never be spaded into the soil, however, since it will not decompose or aid in the fertilization of the soil. This insulating material also may be used to cover a hotbed or coldframe.
Paper mulch has become widely used among amateur gardeners since it was popularized by the pineapple growers of Hawaii, who spread it between the rows of their plants to prevent evaporation. This mulch is a specially prepared paper, black, impervious and tough, and it can be saved and put to use again. For example, spread over seed beds to help with germination, it may be taken up when sprouting begins and placed between the plants to prevent evaporation.
Needs of annual plants
Annual plants require soil that is well supplied with plant food and retains moisture reasonably, while being well drained. Individually, however, these plants have a great difference in requirements. Some need light, some need shade; some will bloom where sown, others do better when transplanted; some need rich soil, others poorer soil; some may be sown before the last frost has come, others must be protected from frost at all times.
Preparing garden soil
In general, a rich, light loam well braced with rotted manure is best for annuals. If the soil is thin and poor, dig a bed 2 feet deep and fill it with soil especially prepared for the specific plants it is intended to grow. For instance, if the plants require heavy soil, use more clay; if they need lighter soils, put in more sand and leaf mold.
A good general purpose soil may be made from so-is of bluegrass with a heavy clay loam rotted for a year, then mixed with equal quantities of rotted manure, leaf mold, and sand. It will not help this specially prepared soil much to give it another coat of manure the second year, but thereafter it should be dressed annually.
When you have good garden soil or other soil of suitable texture at band, it is a common practice to dig the bed and put in this soil, well braced with rotted manure. When making a permanent flower bed it is well worth while to prepare the soil properly. Even if it is not worth the effort to make expensive and costly soil preparations, as in the case of a tenant who will not be in a rented place more than a year or two, good results may still be obtained with annual flowers provided they are selected with full consideration of prevailing conditions.