There's a great deal to know and learn about fertilizers. There are two classes of fertilizers: synthetic and organic. Synthetic fertilizers are those made by chemicals and un-renewable resources. Organic fertilizers are mostly from plant or animal byproducts (such as manure, fish emulsion, worm castings). Here you can learn a little more about both and also learn about macronutrients and micronutrients. For instance, what does the NPK stand for on a fertilizer label? Why do plants utilize macronutrients in greater quantities? And, which nutrients are mobilized in the plant and which are not? One thing is for certain; the micronutrients are just as critical as the macronutrients.
Fertilizers
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Question:
Should I fertilize and water my outdoor plants during the winter?
Answer
Fertilizing of trees and shrubs during the winter in the High Desert should not be done. Fertilizer could stimulate plants to come out of dormancy, start new growth and winter damage could occur. These plants are resting" above the ground but do have activity in the roots if soil temperatures are warm. Normally trees and shrubs that go into winter with adequate soil moisture do not need watering during the winter. Usually winter rains or snow provide enough water. Deciduous plants do not need much water because the leaves, where transpiration occurs, are gone and nutrients needed for growth are not required because there is no shoot growth. The same holds true for most evergreen plants. When the air temperatures are cold and sunlight is reduced, why grow? However, if winter moisture is not sufficient to keep the roots moist they will die. If no winter moisture occurs for four to six weeks then water."
Question:
Should I fertilize and water my house plants during the winter?
Answer
Houseplants are generally tropical in origin and survive best in warm humid environments. Houseplants need to be watered because of the limited soil volume they are confined to. House temperatures are warm and allow plants to continue to grow. The best way to determine soil moisture is to stick a finger in the soil one to two inches. If the soil feels dry, water; if soil feels moist, don't water. Fertilizing houseplants during in the winter months is not encouraged because of reduced light from the sun. However, if you are spoon feeding" your plants, that is giving a little fertilizer at each watering, cut back on the fertilizer by giving 1/3 to 1/2 the normal amount. Many house plants need high humidity to be "happy", this is especially true with ferns. With forced air heating in many homes, house humidity can be lower during the winter than during the hot summer because of swamp cooler use. Humidity can be created by placing the potted plant on top of a pebble filled shallow dish. Fill the dish with water as needed, maintaining the water level near the top. The dish should have a diameter nearly as large as the plant diameter. The pebbles are import so that the potted plant is not sitting in water which will cause soil saturation, and thus root rot. As the water evaporates a humid environment is created in which a tropical plant will grow and thrive. This is much better than using a squirt bottle three times a day to try and humidify the plant!
Question:
How much fertilizer do shade trees need, what kind is the best, and when should it be applied?
Answer
Ornamental trees and shrubs planted in fertile, well drained soil that are growing normally do not need extra nutrients. If they are not doing well fertilization may be helpful but only after the problem causing poor growth is corrected. Symptoms of poor growth may be light green or yellow leaves; smaller and/or fewer than normal leaves or dead spots; wilting of foliage; few flowers; short annual twig growth; and branch tip die back. These symptoms of poor growth may be caused by poor environmental situations like: inadequate soil aeration and moisture, or nutrition; adverse climatic conditions; wrong pH; or insects and diseases. Normally the only nutrient applied to established trees and shrubs in nitrogen. Other situations like chlorotic leaves, manifested by yellowing of leaves but veins remain green, require specific applications of a nutrient, in this case iron. The amount of nitrogen needed will depend on the size of the plant. Measure the diameter of the trunk about one foot from the ground. Apply 0.05 pounds of actual nitrogen/inch of trunk diameter. If a tree has a trunk diameter of six inches multiply by 0.05 to get 0.3 pounds of actual nitrogen. Divide the amount of nitrogen by the percentage of nitrogen content of the fertilizer to be applied. For example: 0.3 pounds of nitrogen applied as 21% ammonium sulfate would be: 0.3/21% = 1.43 pounds of ammonium sulfate fertilizer from the bag. Distribute the fertilizer evenly by measuring the distance between the trunk and drip line and multiply by 125%. This will determine the outer boundary radius for fertilizer application. Distribute the fertilizer evenly in the outer 2/3 of this circle. For example: If the trunk is eight feet from the drip line, then the outer boundary will be ten feet, (8 X 125% = 10). Apply fertilizer around the tree or shrub in a doughnut shaped band this 3.3 feet to 10 feet from the trunk, (10/3 = 3.3). Applications are best applied from early spring.
Question:
I am confused about fertilizers. What do the numbers on the bag mean? What are the differences between organic and chemical fertilizers?
Answer
By law 3 numbers are required on a fertilizer bag. These are the percentage by weight of nitrogen (N), phosphorus (P) and potassium (K) or N-P-K in that order. Therefore, a bag of ammonium phosphate is marked 16-20-0 or 16% N , 20% P, and 0% K. The N is actual total N no matter what the form. P is really the percentage of P205 and K is really percentage of K2O. (A small side-note: to get the actual amount of P you must multiply the number on the bag by 43% and by 83% to get the actual amount of K. These percentages are derived by taking the atomic weight of the element in question and dividing by the atomic weight of the molecule that the element is in. There have been efforts to revise the current labeling of fertilizers so that only the percentage of P and K appear, but these efforts thus far have ended in failure.) Our soils need N for normal plant growth. This is because it leaches from the root zone. N is absorb most of their N in the NH4+ ammonium and NO3- nitrate. These are both inorganic molecules. Generally plants use nitrate form over the ammonium form. Ammonium is converted to N in the soil by aerobic bacteria and some fungi, therefore cool, wet soils have less active bacteria and will yield less nitrate nitrogen. Nitrate forms of nitrogen are taken up by plants directly and is better used in cool, moist soils. Many nitrogen based fertilizers are made by a process which uses atmospheric nitrogen, the air we breath is about 78% nitrogen, and natural gas or methane under high pressure and heat. Organic forms of nitrogen must be mineralized that is converted into inorganic nitrogen by soil microorganisms for plant use. Also the carbonaceous material of the organic matter is broken down in to humus by soil organisms and use N as an energy source. Organic sources of nitrogen included blood meal which is usually around 15% nitrogen. Our desert soils are also low in native phosphorus and should be added at planting time. Phosphorus binds with the soil and does not leach or can not be melted" into the soil with water like nitrogen. There are several forms of phosphorus many being produced by treating phosphate rock with an acid like phosphoric acid. This yield triple super phosphate or 0-45-0 on the fertilizer bag and can be neutralized with ammonia to make ammonium phosphate and liquid fertilizers. Organic forms of phosphorus are available with bonemeal, 0-12-0 being the most common. Potassium is not needed usually in our desert soils. There are many fertilizers on the market which have other nutrients for plant growth. Higher priced fertilizers have some of these nutrients added and increase the cost. Organic based fertilizers like manures and composts have lower plant nutrient levels but add organic matter to our soils and are more beneficial in this regard than chemically based fertilizers. However, the cost and high amounts needed of organic fertilizers for normal plant growth are very high when compared to bagged chemical fertilizers.
Question:
Surflan is called a preemergent herbicides. What does that mean, how and why are they used?
Answer
Preemergent herbicides are a class of weed killers that are applied to the soil before weeds emerge from the ground. The activity of these compounds usually kill germinating seedlings before they emerge from the soil. The new roots and/or shoots absorb some of the material and the plants die. The herbicides are applied to the soil and are usually incorporated into the soil by tillage or irrigation after application. This is necessary because environmental factors such as sunlight cause these products to degrade over time. With pesticides there are several names of each compound that must be understood to avoid confusion. For a single pesticide compound there are three classes of naming. The first is the long chemical name from which a good chemist can reconstruct the molecular structure. The second is the common name, which is registered and approved by the EPA, and is peculiar to that compound no matter who is manufacturer. This common name is analogous a scientific or Latin name of a plant. The third name is the trade name. This name is copyrighted by the seller, but the same chemical can have many trade names. Similar to common plant names. After patent rights expire on the compound anyone can manufacturer the chemical and give it any name they choose. All of this information is found on the label by law. For example a common preemergent herbicide has a chemical name of: 3,5-dintro-N4, N4-dipropylsulfanilamide. The common name is oryzalin. Some trade names are Surflan, (this is the name that the manufacturer uses), Monterey Weed Stopper, or Weed Blocker. The manufacturer sells this compound to others who package Surflan in smaller home use size containers and give their packaged material another name like Monterey Weed Stopper.
Surflan and several other preemergent herbicides are yellow to orange in color. This is because they were synthesized and discovered they had herbicidal activity by the dye industry. Surflan for example is bright orange. When it is being applied by city employees, for example, on median islands or in park landscapes people have become irritated thinking they were using "Agent Orange"! This is not the case. The two are not related. The best time to apply Surflan herbicide in the landscape is in the spring and/or again in the fall. Surflan persist from four to six months depending on environmental conditions. It works well over crushed granite or gravel that does not have plastic under it. Surflan can also be applied to lawns, flower beds (where flower seed is not planted) or transplanted through. Surflan must be watered in within 30 day or it is broken down by sunlight. Here in the high desert it is best to get it watered in with in the first week. With proper and timely application a "weed barrier" is formed and many grasses and broadleaf weeds will be controlled. As with all pesticides read the label and follow all instructions.