In Texas, trees should be fertilized in the Spring and Fall. Any plant must be actively growing for fertilizer to be of any use. Fertilizers are not food. Plants make their own food through photosynthesis, which utilizes the light from the sun to create sugar from carbon dioxide and water. The only thing plants eat is sunlight. To be healthy, all plants require the same sixteen nutrients. When a plant is deprived of any of them the plant becomes sick and dies. This rarely happens because most of these nutrients are already present in the soil. There are times, however, when some of these nutrients are not present in large enough quantities or aren’t available because of the high PH in our soil.
Fertilizers contain varying amounts of macronutrients, which are the three numbers that you see on the bag that you buy, with very small amounts of micronutrients. Fertilizers generally contain large amounts of the macronutrients, with little micronutrients, while bio stimulants contain little macronutrients, large amounts of micronutrients, and beneficial fungi. These fungi work in a symbiotic relationship with the root system, drawing in moisture and nutrients for the plant, and in return the plant feeds it carbohydrates.
How To Use Them
Of the sixteen essential nutrients, carbon, hydrogen, and oxygen are taken from water and air and are always available. The other thirteen are almost always absorbed by the roots. The thirteen essential mineral elements obtained from the soil are divided into three groups based on the amounts of it that are needed by plants. The nutrients that are used in small amounts are called micronutrients or trace elements. These include boron, chlorine, copper, iron, manganese, molybdenum, and zinc. Acid loving plants have trouble obtaining iron in Austin because our soil is so alkaline. The secondary nutrients, calcium, magnesium, and sulfur, are used in greater quantity and deficiencies are more common. Sulfur is often added to good fertilizers that are sold for acid deficient soils, as a buffering agent. At Real Green, we add the sulfur ourselves, to all fertilizers and bio stimulants we apply. Nitrogen (N), phosphorus (P), and potassium (K) are the macronutrients that are needed in the largest quantity. Although these are required in greater quantity, they are no more needed than the micronutrients. Often these nutrients are in the soil but are unavailable because of over fertilization with products that have a high salt content.
Nitrogen: Nitrogen forms new cells and is essential to total plant development. A shortage of nitrogen stops plant growth and cell production. Symptoms of nitrogen deficiency include a yellow-brown color on the veins and tips of the leaves, stunted growth, and pale older leaves. Too much nitrogen can cause tall, spindly plants that easily topple over and nitrate poisoning, which makes leaves red. Nitrogen is also essential to compost piles, as it aids in the breaking down of old plant residues. Good sources of nitrogen include: blood meal, cottonseed meal, fish meal, soybean meal, rabbit manure and tea grinds. You can also grow a cover crop of legumes in the fall to raise the nitrogen level.
Phosphorus: Phosphorus produces vigorous seed and root development. A shortage of phosphorus slows cell division and results in stunted growth and late maturity. A symptom of phosphorus deficiency is spindly plants with purple streaks in the stems. Since phosphorus moves slowly in the soil, it is essential to have it available during early plant development. Good sources for phosphorus include: bone meal, rock phosphate and colloidal phosphate. Incorporating organic matter into the soil makes the phosphorus there more available to the plants.
Potassium: Also called Potash, this nutrient helps produce strong and sturdy stems. It advances root growth and helps plants resist disease and cold weather. A shortage of this nutrient causes stunting and stem weakness. Symptoms include yellowing of leaf edges leaf veins. This nutrient must be available during early plant development. Good sources of potash are: cow manure, compost, granite meal, greensand and wood ashes.
pH – pH is a measure of acidity or alkalinity on a scale of 0 to 14, with 7 being neutral. The pH of the soil affects many elements including nutrient availability, plant nutrient uptake, and microorganism activity. Because soil pH affects many factors, it’s important to maintain proper pH through the growing season. Considering the complexity of factors involved, the recommended soil pH for each individual variety is very important. pH testing will let you make informed decisions if a soil pH adjustment is needed.
For soils that are too acidic, add lime to the soil in the fall. Some sources of lime are: Dolomitic limestone. This will raise the pH of the soil while supplying calcium and magnesium. Apply in late fall for next year. Hydrated lime will provide quicker results because of the smaller particle size and is especially useful for raising the soil pH quickly. Be aware that hydrated lime may injure young plants. Apply at least 3 weeks before planting your crops. Wood ashes can also be added to acidic soil to correct the pH level.
For soils that are too alkaline, add powdered agricultural sulfur, aluminum sulfate or iron sulfate to the soil. For a long term solution, continually add acidic organic matter to the soil, such as peat moss, pine needles and oak tree leaves until the pH level is correct.
Lawn fertilization is applied on the surface and rarely reaches the root system of a tree. Furthermore, many lawn fertilizers actually contain a herbicide. These fertilizers are called a “Weed and Feed”. These herbicides are targeted towards broad leafed plants (weeds). The big problem here is that trees are also broad leafed plants, and these herbicides can kill trees. Some trees will become sick after one application, while others can withstand many years of repeated applications before becoming ill. Another issue is timing; Pre-emergent herbicides should be applied when everything is dormant, while fertilizers are only effective when plants are growing. Trees are targeted by many defoliating pests. These pests can strip a tree in days. A healthy tree has the ability to replace this damage, as well as fight other fungal and disease problems. Without foliage, a tree has no way of feeding itself.