SOIL

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SOIL
[13.1]

Of all the factors involved in growing plants, soil is the most complex. It has its own ecology, which can be modified, enriched, or destroyed; the treatment it receives can ensure crop success or failure.

There is no such thing as the perfect soil for Cannabis. Each variety can grow within a wide range of soil conditions. Your goal is garden soil within the range for healthy growth: well-drained, high in available nutrients, and with a near neutral (7.0) pH. Cannabis grows poorly, if at all, in soils which are extremely compacted, have poor drainage, and low in fertility, or have an extreme pH.

There are several soil factors that are important to a grower; these include soil type, texture, pH, and nutrient content. We will begin this chapter by discussing each of these topics in succession, and will then turn to discussion of fertilisers, soil-preparation techniques, and guerilla farming methods.

Types of Soil
[13.2]

Each soil has its own unique properties. These properties determine how the soil and plants will interact. For our purposes, all soils can be classified as sands, silts, clays, mucks, and loams. Actually, soils are usually a combination of these ingredients. If you look carefully at a handful of soil, you may notice sand granules, pieces of organic matter, bits of clay, and fine silty material.

Sandy Soils
Sands are formed from ground or weathered rocks such as limestone, quartz, granite, and shale. Sandy soils may drain too well. Consequently, they may have trouble holding moisture and nutrients, which leach away with heavy rain or watering. Some sandy soils are fertile because they contain significant amounts (up to two percent of organic matter, which also aids their water-holding capacity. Sandy soils are rich in potassium (K), magnesium (Mg), and trace elements, but are often too low in phosphorous (P) and especially nitrogen (N). N, which is the most soluble of the elements, is quickly leached from sandy soil. Vegetation on sands which is pale, yellowed, stunted, or scrawny indicates low nutrients, usually low N.

Sandy soils can be prepared for cultivation without much trouble. They must be cleared of ground cover and treated with humus, manure, or other N-containing fertilisers. In dry areas, or areas with a low water table, organic matter may be worked into the soil to increase water-holding capacity as well as fertility. Sandy soil does not usually have to be turned or tilled. Roots can penetrate it easily, and only the planting row need be hoed immediately before planting. Growers can fertilise with water-soluble mixes and treat sandy soil almost like a hydroponic medium.

Sandy soils are also good candidates for a system of sheet composting (spreading layers of uncomposted vegetative matter over the garden), which allows nutrients to gradually leach into the soil layers. Sheet composting also prevents evaporation of soil water, since it functions as a mulch.

Silts
Silts are soils composed of minerals (usually quartz) and fine organic particles. To the casual eye, they look like a mucky clay when wet, and resemble dark sand or brittle clods when dry. They are the result of alluvial flooding, that is, are deposits from flooding rivers and lakes. Alluvial soils are usually found in the Midwest, in valleys, and along river plains. The Mississippi Delta is a fertile alluvial plain.

Silts hold moisture but drain well, are easy to work when moist, and are considered among the most fertile soils. They are frequently irrigated to extend the length of the growing season. Unless they have been depleted by faulty farming techniques, silts are rich in most nutrients. They often support healthy, vigorous vegetation. This indicates a good supply of N.

Mucks
Mucks are formed in areas with ample rainfall which supports dense vegetation. They are often very fertile, but may be quite acidic. They usually contain little potassium.

Mucks range from very dense to light sandy soils. The denser ones may need heavy tilling to ensure healthy root development, but the lighter ones may be cleared and planted in mounds. Mucks can support dense vegetation, and are often turned over so that the weeds thus destroyed form a green manure.

Clay Soils
Clays are composed of fine crystalline particles which have been formed by chemical reactions between minerals. Clays are sticky when wet, and can be moulded or shaped. When dry, they form hard clods or a pattern of square cracks along the surface of the ground. Clays are usually hard to work and drain poorly. Marijuana roots have a hard time penetrating clay soils unless these soils are well-tilled to loosen them up. Additions of perlite, sand, compost, gypsum, manure, and fresh clippings help to keep the soil loose. Clay soils in low-lying areas, such as stream banks, may retain too much water, which will make the plants susceptible to root and stem rots. To prevent this, some growers construct mounds about six inches to one foot high, so that the stems and tap roots remain relatively dry.

Clay soils are often very fertile. How well marijuana does in clay soils usually depends on how well these soils drain. In certain areas "clay" soils regularly support corn cotton. This type of soil will support a good crop of marijuana. Red colour in clay soil (red dirt) indicates good aeration and a "loose" soil that drains well. Blue or gray clays have poor aeration and must be loosened in order to support healthy growth.

A typical schedule for preparing a heavy clay soil In the late fall, before frost, turn soil, adding fresh soil conditioners, such as leaves, grass clippings, fresh manure, or tankage. Gypsum may also be added to loosen the soil. Spread a ground cover, such as clover, vetch, or rye. In early spring, making sure to break up the large clods, and add composts and sand if needed. At planting time, till with a hoe where the seeds are to be planted.

As the composts and green manure raise the organic level in the soil, it becomes less dense. Each year, the soil is easier to work and easier for the roots to penetrate. After a few years, you may find that you only need to turn under the cover crop. No other tilling will be needed.

Loams
Loams are a combination of about 40 percent each of sand and silt, and about 20 percent clay. Organic loams have at least 20 percent organic matter. In actuality, a soil is almost always a combination of these components, and is described in terms of that combination, e.g., sandy silt, silty clay, sandy clay, or organic silty clay. Loams range from easily worked fertile soils to densely packed sod. Loams with large amounts of organic matter can support a good marijuana crop with little modification.

Humus and Composts
[13.3]

Humus and composts are composed of decayed organic matter, such as plants, animal droppings, and microbes. Their nutrient contents vary according to their original ingredients, but they most certainly contain fungi and other microorganisms, insects, worms, and other life forms essential for the full conversion of nutrients. As part of their life processes, these organisms take insoluble chemicals and convert them to soluble forms, which plant roots can then absorb. Humus and composts hold water well and are often added to condition the soil. This conditioning results from the aerating properties and water-holding capacity of humus and composts, as well as balanced fertility.

Humus and composts have a rich, earthy small, look dark brown to black, and may contain partially decayed matter, such as twigs or leaves. They are produced naturally as part of the soil's life process or can be "manufactured" at the site by gathering native vegetation into piles. Composts cure in one to three months, depending on both ingredients and conditions. Decomposition can be speeded up by turning and adding substances high in N. Composts are frequently acidic and are sweetened with lime when they are piled. This also shortens curing time, since the desirable microbes prefer a neutral medium.

Texture
[13.4]

Soil texture refers to density, particle size, and stickiness, all of which affect the soil's drainage and water-holding characteristics. The most important quality of the soil for marijuana is that it drains well - that is, water does not stand in pools after a rain, and the soil is not constantly wet. In a well-drained soil, the roots are in contact with air as well as water.

Cannabis does best on medium-textured soils: soils that drain well, but can hold adequate water. Loams, silts, and sands usually drain well and are loose enough to permit good root development. Some clays and most mucks are too compact to permit the lateral roots to penetrate and grow. In addition, they often drain poorly, and when dry they may form hard crusts or clods, a condition marijuana cannot tolerate.

Several simple tests will indicate the consistency and drainage qualities of your soil. Test when the soil is moist but not wet. First, dig a hole three feet deep to check the soil profile. In a typical non-desert soil, you will find a layer of decaying matter on the surface, which evolves into a layer of topsoil. Most of the nutrients available to the plant are found at this level or are leached down from it. The topsoil layer is usually the darkest. It may only be an inch thick or may extend several feet. When in good condition, the topsoil is filled with life. Healthy topsoil contains abundant worms, bugs, and other little animals, and is interlaced with roots. If you can easily penetrate the underlying topsoil with your hands, its texture is light enough for healthy root growth.

The next layer, or subsoil, may be composed of a combination os sand, clay, and small rocks, or you may hit bedrock. Sandy, rocky, and loamy subsoils present no problems as long as the topsoil is at least six inches thick. Clay or bedrock often indicates drainage problems, especially if the spot has a high water table and stays wet.

Next scrape up a handful of soil from each layer. Press each handful in your fist, release it, and poke the clump with a finger. If it breaks apart easily, it is sandy or loamy. Clods that stick together, dent, or feel sticky indicate clay or muck.

To test for drainage, fill the hole with water. Wait half an hour to let the moisture penetrate the surrounding soil; then fill the hole with water again. If the water drains right through, you are working with sandy soil. If it doesn't drain completely within 24 hours, the soil has poor drainage.

pH
[13.5]

The pH is a measure of how alkaline (bitter) or acid (sour) the soil is. The pH balance affects the solubility of nutrients, and helps the plant regulate metabolism and nutrient uptake. The scale for measuring pH runs from 0 to 14, with 7 assigned as neutral. A pH below 7 is acid; a pH above 7 is alkaline.

Marijuana grows in soils with a pH range from 5 to 8.5, but it thrives in nearly neutral soils. Relative to other field crops, it has high lime requirements, similar to those for red or white clover or sunflower. But it does well in fields where plants with medium lime requirements, such as corn, wheat, and peanuts, are grown.

The solubility of nutrients is affected by soil type as well as by the pH. In soils with a high content of organic matter, all nutrients are soluble between 5.0 and 6.5. Phosphorous, manganese, and boron are less soluble at pH values above 6.5. Acid soils are usually found in the United States east of the 100th meridian and along parts of the West Coast, and a deep topsoil layer. Marijuana does best in acid soils when the pH is adjusted to a range of 6.3 to 7.0. {Figure 58. Map of pH for US.}

Mineral soils in the dry western states may be slightly acid to highly alkaline. Most nutrients are very soluble in these soils, as long as the pH ranges from 6.0 to 7.5. Some of these soils are too alkaline (over 8.5); so their pH must be adjusted to near neutral to ensure healthy growth.

Adjusting the pH

First test the soil pH in the garden area. Previous gardeners may have adjusted native soils, or your yard soil may have been trucked in to cover poor native soils, so that the pH of your garden soil may be different from that of other soils in the area. Different soils vary in the amount of material needed to adjust the pH. Sandy soils do not require as much as loam, and loam requires less than clays, partly because of the chemistry, and partly because of the density and physical qualities of the soils' particles.

Adjusting Acid Soils
Acidic soils are treated with limestone, which is expressed as an equivalent of calcium carbonate (CaCO3). Limestone is usually quarried and powdered, contains large amounts of trace elements, and comes in different chemical forms: ground limestone, quicklime, and hydrated lime (which is the fastest acting form). Dolomitic limestone is high in magnesium and is often used to adjust magnesium-deficient soils, such as those found in New England. Marl (ground seashells) is also mostly lime and is used to raise soil pH. Eggshells are another source of lime. They should be powdered as finely as possible, but even so, they take a long time to affect the soil. Wood ashes are alkaline and very soluble; so they have an almost immediate effect.

Every commercial lime has a calcium carbonate equivalent or neutralising power which is listed on the package. To find out how much to use, divide the total amount of limestone required by the pH test (see Figure 59) by the calcium carbonate equivalent. For instance, a field requires fifty pounds of limestone, but the calcic limestone you are using has an equivalent of 1.78. Divide the 50 by 1.78. The resulting figure, about 29 pounds, is the amount required. Commercial limes also list the grade or particle size of the powder. In order of fineness they are: superfine, pulverised, agricultural grade, and fine meal. The finer the grade, the faster the action. {Figure 59. Approximate amount of lime required to adjust pH of a 7" layer of different types of soil.}

For best results, lime should be added at least four or five months before planting. In this way, the lime has a chance to react with the soil. But acid soils can be limed profitably and time before planting, or after, as long as the lime does not come into direct contact with the plants. Most growers add lime at the same time that they fertilise and turn the soil. That way, tilling and conditioning are handled in one operation. The lime should be worked into the soil to a depth of ten inches. Lime can also be added by spreading it before a rain. Make sure that the soil is moist enough to absorb the rain, so that the lime does not run off. Growers who have not adjusted the pH can dissolve lime in water before they irrigate. However, this is not advised if the water runs through a hose or pump, because mineral buildup may occur in the equipment.

Adjusting Alkaline Soils
Most alkaline soils have a pH no higher than 7.5, which is within the range for optimum growth. Soils that are too alkaline can be adjusted by adding gypsum, which frees insoluble salts, and include iron, magnesium, and aluminium sulphate. Marijuana has a low tolerance for aluminium; so marijuana growers should use iron or magnesium sulphate in preference to aluminium sulphate. Sulphur and gypsum are worked into the soil in the same manner as lime.


{Table 19.}
Some growers correct alkaline soils by adding an organic mulch or by working acidic material into the soil. Cottonseed meal, which is acidic and high in nitrogen, can also be used. As it breaks down, cottonseed meal neutralises the soil. Pine needles, citrus rinds, and coffee grounds are all very acidic, and can be used to correct alkaline conditions. The addition of soluble nitrogen fertilisers aids the breakdown of these low-nitrogen additives. (See Table 22 in the section on "Fertilisers" in this section.)

Adjusting Alkali Soils
Alkali soils (pH usually above 8.5) are hardpacked and crusty, and sometimes have an accumulation of white powdery salts at the surface. They may not absorb water easily and can be extremely difficult to work. To prepare alkali soils with a permeable subsurface for cultivation, farmers leach them of their toxic accumulation of salts. The soils is thoroughly moistened so that it absorbs water. Then it is flooded so that the salts travel downward out of contact with the roots. Gypsum can be added to free some of the salts so that they leach out more easily. Gypsum can be added at the rate of 75 lbs per 100 sq.ft., or 18 tons per acre. Leaching requires enormous quantities of water, an efficient irrigation system, and several months.