Most of the nutrients needed for the growth and development of plants are absorbed from the soil by the roots. Over the seasons, these soil nutrients become depleted and must be replenished or our garden plant health will decline.
There are 17 chemical elements known to be essential for plant growth, flowering, and fruiting.
The primary macronutrients, nitrogen (N), phosphorus (P), and potassium (K), are used in the largest amounts by plants and are thus prone to deficiency in soils. These nutrients are the primary ingredients in most garden fertilizers and the percentages of each are prominently displayed on the bag as the N-P-K numbers. These percentages are always presented in the same order - nitrogen, phosphorus, potassium.
Nitrogen is required for healthy vegetative growth (leaves and stems) and is especially important in young plants. High levels promote dark green leafy growth but not fruits and flowers. Thus a fertilizer higher in nitrogen is great for lawns and leafy vegetables but disastrous when you are trying to grow tomatoes!
Phosphorus is important in all functions of plant growth but especially for root development and growth, and in the production of flowers, fruits, and seeds. Starter fertilizers, which can be used when transplanting trees, shrubs, and perennials, are much higher in phosphorus than nitrogen and potassium. They stimulate root growth and help avoid transplant shock. “Bloom booster” fertilizers with 20%-30% phosphorus help promote flower bud formation.
Potassium is important for the overall vigor of plants. It promotes disease resistance, root formation, and cold hardiness. Plants deficient in potassium will have weak roots and stems.
A complete fertilizer supplies all of the primary macronutrients in varying amounts. Depending on your needs, you might pick one with higher nitrogen, higher phosphorus, or higher potassium.
A balanced fertilizer supplies equal amounts of each of the 3 nutrients. These fertilizers, such as 10-10-10, are often used for general applications.
Single element fertilizers (straight or incomplete fertilizers) supply only one of the primary nutrients, e.g. Espoma Urea (45-0-0), Triple Super Phosphate (0-45-0), or Potash (0-0-60).
The secondary macronutrients are calcium (Ca), magnesium (Mg), and sulfur (S). These nutrients are very important to plants but are used in smaller amounts than the three primary macronutrients.
Micronutrients, also known as trace elements, are not nutrients of lesser importance to plant health but those that are required in minute quantities. With the exception of iron and manganese, micronutrients are seldom deficient in our garden soil, however, some can become unavailable to plants when the soil pH is either too high (alkaline) or too low (acidic). Maintaining your soil pH between 6.0-6.5 will keep these nutrients available to the plants. Some fertilizers are fortified with micronutrients.
There are several ways to improve the fertility of your soil but the most common way is to apply fertilizers, either organic or synthetic (chemical fertilizer). There are advantages and disadvantages to using either form, however, in André’s opinion, organics are by far the way to go.
Organic fertilizers such as the Espoma “Tones” release nutrients slowly over time. They rely on soil organisms to break the nutrients down into a form that the plants can use. Because they are slow release, they are applied less often than chemical fertilizers. Organic fertilizers are usually applied once in the spring and again in the fall. Organic fertilizers rarely burn the roots or foliage of your plants.
Synthetic fertilizers generally provide nutrients in a form that is available to the plants right away; they don't have to be broken down by soil organisms first. Although there are some slow release synthetic fertilizers, most are water soluble and release nutrients quickly. This provides a quick boost to the plants. Unfortunately, these readily available nutrients can leach out of the root zone fairly quickly so these fertilizers must usually be reapplied more frequently than organic fertilizers. In addition, excess nutrients that the plants aren't able to absorb are more likely to leach into the groundwater. Synthetic fertilizers are usually more concentrated than organic fertilizers and must be applied carefully to avoid damage to growing plants.
More significantly, organic fertilizers add all important organic matter to the soil, thus improving soil structure. Remember, good soil structure improves drainage in clay soils and increases the water-holding capacity of sandy soils. Some organic fertilizers including the Espoma "Tones" add beneficial microbes and mycorrhizal fungi as well as nutrients to the soil. The benefits of mycorrhizal fungi in garden soil are becoming increasingly recognized worldwide.
Mycorrhizal fungi form a symbiotic relationship with plant roots to improve the uptake of water and nutrients. Tremendous numbers of mycorrhizal threads attach to the roots of plants and then fan out into the surrounding soil. These "extensions" of the root system exponentially increase the area that a plant can exploit for the raw materials needed for growth. The mycorrhizal filaments capture and assimilate nutrients, minerals, and water which can then be transferred to the plant. This relationship has been shown to greatly increase plant tolerance to drought stress and reduce transplant shock. In addition, mycorrhizals are known to secrete chemicals which dissolve hard to capture nutrients like phosphorus and iron, making them more available to plants. They even produce antibiotics which attack and kill many disease organisms that enter the "root" zone!
Espoma has now incorporated mycorrhizal fungi and other beneficial microbes into many of their organic potting mixes and garden soils. The addition of Myco-tone, a proprietary blend of 11 different strains of mycorrhizae, has been proven to promote root growth, increase water uptake, and reduce drought stress and transplant shock.