Preparing Soil for the Outdoor Season
All soil isn’t created equal. For a soil to really help plants and crops maximize growth and production, essential elements and nutrients are required. Eric Hopper explains what separates great soil from bad soil.
The most significant advantage of gardening outdoors is access to the ultimate energy source: the sun. There is simply no artificial lighting that can compare. However, for outdoor crops to reach their full genetic potential, they must have access to more than sunlight. Specifically, essential and beneficial elements must be available. The essential non-mineral elements (hydrogen, oxygen, and carbon) are obtained via water and air and as long as there is rain or irrigation, an outdoor garden will get the non-mineral elements.
Unlike the non-mineral elements, the essential and beneficial mineral elements are provided to the plant through the soil. To maximize performance, a grower must ensure his or her soil contains all the essential and beneficial elements.
Essential Mineral Elements
The essential mineral elements can be classified as either macro- or micronutrients. The macronutrients are the nutrients used in higher concentrations relative to micronutrients, which are absorbed in smaller amounts. The essential macronutrients are nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). The essential micronutrients are chlorine (Cl), iron (Fe), boron (B), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and nickel (Ni). Micronutrients, although absorbed in lower amounts than macronutrients, play an equally important role in plant health and crop production. A well-balanced soil will always have the essential elements (both macro- and micronutrients) available to plants.
In addition to the essential mineral elements, there is another set of mineral elements used by plants. These elements are called beneficial elements. Beneficial elements are not necessarily required for plant functions, but they have been found to show various favorable characteristics. The beneficial elements are silicon (Si), cobalt (Co), selenium (Se), and sodium (Na).
Soil vs Dirt
In organic gardening, soil isn’t just dirt. Instead, soil is considered a living organism chock-full of beneficial microorganisms. Soil will also contain organic material and/or ingredients that, as they are broken down by microorganisms, are converted into nutrients for plants. Although the terms dirt and soil are often used synonymously, they are not the same in terms of organic gardening. However, by amending ingredients rich in macro- and micronutrients, beneficial elements, and beneficial microorganisms, just about any substrate or dirt can be converted into a rich, living soil.
A good place to start when building an organic outdoor soil is to add compost material. Compost is a general term referring to composted (aged and broken down) organic matter and can be derived from a number of different sources but is usually derived from plant material and/or manure. Compost will contain a good level of essential elements in both macro- and micronutrients. Not only does compost provide significant nutritional value, it also adds an abundance of microbial life to the soil. These beneficial microorganisms are the foundation for nutrient uptake and aid in the stimulation of new root development.
Like compost, worm castings (or vermicompost) are a significant source of both macro- and micronutrients and beneficial microorganisms. Worm castings are known to enrich soils and improve disease resistance in crops. If using worm castings as a soil additive, be sure to purchase pure worm castings. There are many products on the market that are labeled as worm castings, but many contain only a small percentage of actual worm castings in their composition.
Organic Dry Ingredients
In addition to compost and/or worm castings, it is beneficial to add individual organic dry ingredients to soil. Individual organic dry ingredients can be added in various quantities, depending on the crop being grown. Generally, an organic soil with a wide variety of ingredients ensures the plants receive everything they need. However, some crops may require specific nutrients. Individual organic dry ingredients allow the cultivator to tailor the soil composition to the specific crop.
The following ingredients are commonly used by organic cultivators to amend their outdoor soil. These can be mixed (amended) into the soil at the beginning of the season and/or used as a top-dressing as needed:
Blood meal is a very rich, fast-releasing nitrogen source. Blood meal is a great additive for plants requiring high amounts of nitrogen.
Fish meal is another fast-releasing nitrogen source. Fish meal is a great nitrogen additive that enhances microbial life in the soil and also contains a significant amount of phosphorus, which helps trigger root development.
Feather meal is a slow-releasing nitrogen source best used for plants requiring high amounts of nitrogen over a three to four month period.
Soybean meal is a slow-releasing nitrogen source, but not quite as slow as feather meal. Soybean meal is a great additive for plants needing adequate nitrogen for two to three months and a little phosphorus boost to help promote fruiting or flowering.
High-nitrogen bat guano is rich in micronutrients, beneficial microbes, and, of course, nitrogen. The fast-releasing nitrogen and its beneficial diversity make high-nitrogen bat guano the fertilizer of choice for many organic growers.
High-phosphorus bat guano is an excellent source of phosphorus and is known to not only increase flower/fruit sets, but also their size, aroma, and flavor. Many brands of high-phosphorus bat guano are also a great source of calcium.
Bone meal is an excellent phosphorus source and is revered for its ability to promote strong root development. Bone meal is also a great source of calcium.
Fish bone meal is basically the same thing as bone meal except it is derived from fish. A great source of both phosphorus and calcium.
Seabird guano, like bat guano, is known to increase the amount of flower/fruit sets and their size. An excellent source of phosphorus and micronutrients.
Rock phosphate is a slow-releasing phosphorus source that is commonly extracted into a liquid form to increase availability. Best used for plants needing a slow and constant release of phosphorus.
Hardwood ash is the original source of “potash” fertilizers. Hardwood ash can be used as a direct soil additive to increase potassium levels.
Kelp meal is a source of readily available potassium and a variety of micronutrients and plant hormones. This great soil additive can also increase overall plant health and vigor.
Greensand is a slow-releasing potassium source. Generally speaking, greensand is used to improve a soil’s condition rather than boost potassium content.
Langbeinite is a naturally occurring mineral and is water soluble. It’s a good source of potassium, sulfur, and magnesium.
Oyster shell is an excellent source of calcium that accelerates root development and, in turn, improves nutrient uptake. Oyster shell also works as a pH buffer, helping to keep the soil from becoming too acidic.
Dolomite lime, or sweet lime, is a great pH buffer for any soil composition and ensures the soil’s pH doesn’t turn too acidic. Also a rich source of calcium and magnesium.
Glacier rock dust is a soil amendment that revitalizes trace elements and provides a foundation of minerals for healthy plant growth.
Alfalfa meal is rich in trace elements, but it is the abundance of natural growth stimulators that has gained recognition among organic horticulturists. Alfalfa meal accelerates growth rates while promoting abundant fruit or flowers.
Although many of the commonly used soil ingredients already contain a good level of beneficial microorganisms, many organic gardeners supplement additional microorganisms into their soil compositions. Three beneficial microorganisms commonly used by horticulturists are trichoderma, mycorrhiza, and bacteria. Beneficial microorganism products can be amended to a soil or top-dressed to help increase the number of beneficial microbes.
By building or amending an outdoor soil to make it a living soil full of microbial life and nutrition, a cultivator is giving his or her plants the opportunity to live up to their full potential. As a grower becomes more familiar with individual organic ingredients, he or she can tailor the soil composition to the needs of a particular crop. Many annual plants with separate vegetative and flowering cycles will respond best to the top-dressing of specific dry ingredients during transitional stages or during the fruiting/flowering stage. For example, as a tomato plant starts to fruit, a grower could top-dress ingredients with a higher ratio of phosphorus and potassium, as those best match the nutritional requirements of tomatoes during that growth stage. A well-balanced living soil with a wide variety of ingredients will generally supply a garden with all the essential and beneficial elements needed for healthy growth. The additional amendments and/or stage-specific additives will only increase performance and are considered the icing on the cake.
Written by Eric Hopper | Writer, Consultant, Product Tester
Eric Hopper’s past experiences within the indoor gardening industry include being a hydroponic retail store manager and owner. Currently, he works as a writer, consultant and product tester for various indoor horticulture companies. His inquisitive nature keeps him busy seeking new technologies and methods that could help maximize a garden’s performance.