We gardeners know what good soil looks like, smells like and feels like. We know its value and that without it all our gardening efforts are futile. Someone once said that 50 percent of your chance of having a successful garden is already determined before you put the first seed into the ground. The point is that soil conditions play a major role in plant health and productivity. Great varieties, fantastic fertilizers, elaborate irrigation systems and magic tonics cannot make up for lousy soil.
Unfortunately, whenever we move into a new place or decide to take up gardening for the first time, the soil we usually start off with is not fit for weeds. When starting to garden a new spot I consider it a personal challenge to turn that patch of earth into something you can stab a pencil into and have it start to root and grow. The good news is that almost any soil can be made fertile and productive.
There are several factors that determine a soil’s suitability for supporting a successful garden. Nutrient content is one of the first of these to consider. There are a number of different nutrients needed in various quantities by growing plants. Those needed in the largest amounts we call primary nutrients. Nitrogen, phosphorus and potassium are primary nutrients.
Secondary nutrients are calcium, magnesium and sulfur. These are needed in smaller amounts. Minor nutrients, including iron, manganese, zinc, boron, copper, molybdenum and chlorine are as important to plant growth as the big three, but are only needed in very small amounts. A deficiency of any one nutrient limits plant performance, sort of like the old adage that a chain is only as strong as its weakest link.
The ratio between nutrients is also important. An excess of one nutrient can cause problems with another. Phosphorus for example can tie up iron, making it unavailable to growing plants. Additionally, soil pH affects nutrient availability. High (alkaline) and low (acidic) pH levels can both result in nutrient deficiency symptoms in your garden even though hose nutrients are present in the soil. This is why pecans growing on high pH soils often suffer from zinc deficiency.
Texture describes the type and size of particles that make up a soil. Sand, silt and clay are three basic texture types. Sand particles are like large boulders next to the tiny silt particles and the infinitely smaller clay particles. Sand drains well but does not hold moisture or nutrients very readily. Clay on the other hand drains very slowly but holds water and nutrients very well.
Structure is the way the soil particles group together. Some clays are very "massive," forming solid, impervious blocks that are as hard as concrete when dry. Such impervious clays may be great for lining a farm pond, but are not what we need in the garden.
Others clays are made up of particles that group into looser clumpings of particles giving them a loose structure that we refer to as "friable." Grab a large clod of such a clay and it will easily crumble in your hand with a little pressure. Clays with good, friable structure are better aerated and drain better than those with poor structure.
Organic matter is truly the key to great soil. It helps sand hold water and nutrients better and helps clay form better structure, thus improving the quality of both for plant root growth. Our Texas soils are notoriously low in organic matter content. We "burn it up" as fast as the cycle of nature can produce it. In order to increase our garden soil’s organic matter content we need to add more on a regular basis.
I must admit that I am not a fan of "rule of thumb" fertilizer recommendations. The perfect fertilizer for that next planting of broccoli, for example, depends on what is already in the soil. The soil phosphorus levels may be excessive and the potassium deficient or vice versa. With a soil test you can know just what is needed to bring things back into balance. Years of using 13-13-13 or 10-20- 10 fertilizer have created phosphorus excesses in many garden and landscape soils. Rather than fertilize by a formula year after year, have your soil tested.
Soil test every year for two or three cycles when you start a new garden area. After that, testing every 3 or 4 years is probably often enough. It takes time to bring about some changes in the soil. Lime, used to raise pH, and sulfur, used to lower pH, may take months to a year or more to take their full effect.
There is no single ingredient or fertilizer that can make the positive difference in your garden soil than compost can. Nature makes its own compost as leaves and grass clippings and other and slowly decompose back into the soil.
The plant materials that are composted are filled with the nutrients those plants took up through their roots during the growing season. Thus these composted materials are perfect for replenishing nutrients back into the soil. However, compost does much more than add nutrients and improve structure, although that alone makes it worth its weight in gold.
Compost is alive with billions of microbes. These microscopic organisms break down the organic matter and release its nutrients. They also secrete substances that help glue soil particles together forming better structure. Their activity produces organic acids that help dissolve soil minerals releasing more nutrients into a nutrient-rich "soup" on the surface of the soil particles. This creates a perfect environment for plant roots to grow and thrive. Regular additions of compost help moderate extremes in soil pH as well as eliminate the effects of certain nutrient deficiencies and excesses.
Additionally, compost makes the soil more attractive to earth-worms. These "miners of the soil" do a tremendous service by opening up passageways through the soil. Secretions from their bodies glue soil particles together and help form tunnels that loosen the soil.
These tunnels also improve aeration into the lower soil pro-file. They enhance a soil’s ability to take in rainwater thereby reducing runoff. Over time their activity is an important factor in developing good soil structure. Earthworms are part of the process of turning the soil as they bring organic matter to lower levels while leaving their castings on the surface as a nutrient rich fertilizer for our gardens.
When a soil test indicates a particular nutrient is lacking, it Iron chlorosis on blackberries shows up as a yellowing of new growth. While there are a number of synthetic fertilizers that can effectively fix a nutrient problem, many gardeners prefer to use natural products whenever avail-able. Natural fertilizers include those of plant and animal origin and certain "mined" products.
Natural sources of nitrogen include blood meal (12-2-0), fish meal (10-6-0), and cottonseed meal (6-3-1.5). Sources of phosphorus include bone meal (raw 3-22-0) (steamed 1-15-0), and rock phosphate (0-20-0). Potassium-rich natural fertilizers include greensand (0-1-4), and supposal also known as Knag (0-0-22). In addition to these, wood ashes from the fireplace contain a 0-2-6 ratio of nutrients, but are very high in pH and should therefore be avoided on high pH soils.
Additionally, there are a couple of great choices for foliar feeding or for a starter solution for new transplants. Seaweed provides a minor source of plant nutrients along with many other health-promoting plant sub-stances. Fish emulsion is also a great way to provide a quick nutrient boost. Soil tests often indicate a need for fertilizers in a 3-1-2 or 4-1-2 ratio of nutrients as this is the blend that turf and many ornamental and vegetable plants need. Natural blends like 8-2-4 and 6-2-2 are now available for such needs.
Of course we cannot leave out manure. Whatever is available locally is probably your best bet. In general, horse and cow manure is lower in nutrients than poultry manures. My personal favorites are rabbit and sheep manure. Their balance of nutrients is great for most garden plants.
A word of caution is in order. Avoid manure from cattle grazed on pastures treated with broadleaf herbicide products. Certain types of these products can still be present in the manure at concentrations high enough to damage tomatoes and other sensitive species of vegetable crops.
Green manure crops are plantings grown to later mow and turn under to build the soil. There are many different crops that could be used in this way. Some are legumes, fixing nitrogen into the soil in nodules on their roots. Others are not legumes but produce significant amounts of top and root growth, which helps add lots of organic matter to the soil. The chart shown below gives a few suggestions, with their growing season. While very few of us start with great soil, it is most definitely something we can build over the years. So if you are struggling with an unproductive garden patch or flower beds, banging a rototiller over the concrete clay or watching nutrients and water disappear into a lifeless sand, now is the time to turn it all around. Remember to start with a few inches of compost, nature’s living fertilizer, and add another inch or so every time you transition from one planting season to another. You will find your gardens more healthy and productive, and gardening a whole lot more rewarding, too.