COLUMN: Linn Mills

     I am always asked which fertilizer is best. There is no best fertilizer. It depends on what you want. Fertilizer with nitrogen gets plants to green up and grow. Use phosphorous to help roots, flowers and fruit. Add potassium to build quality and disease resistance into your favorite plants. It sounds so simple, but it is not. Each nutrient has its job. When they all come together in the right combination, you can expect "blue ribbon" plants in your yard.
      Today, I want to focus on fertilizers and what these fundamental building blocks of plant nutrition do for your plants.
      You will find all kinds of fertilizer on the nursery shelves. You'll find some blended for specific crops such as roses and tomatoes, while others will be straight nitrogen or phosphorous. Whatever bag you choose, there will always be three numbers on the bag; it's the law. You'll find combinations such as 16-6-8; 6-6-6; 5-10-5; 16-20-0; 25-3-6; 33-0-0; 21-0-0 and so on.
      The first number in the sequence always represents the percentage of nitrogen, the second the percentage of phosphorous and the third the percentage of potassium; these are the fundamental building blocks of plant nutrition. A 16-6-8 fertilizer has 16 percent nitrogen to 6 percent phosphorus to 8 percent potassium. They add up to 30 percent. Suppose you had a 100-pound bag of 16-6-8 fertilizer. You'd have 30 pounds of fertilizer and 70 pounds of inert material -- the stuff for the fertilizer to cling to for easier handling, storing and spreading.
      Nitrogen is the primary nutrient needed for normal plant growth. Compared with the other essential nutrients, nitrogen is the one absorbed by plants in the greatest quantities. It imparts to leaves and stems a characteristically deep green, healthy color. The most apparent function of nitrogen is the encouragement of above-ground growth. But take note: it is very soluble, so it leaches easily beyond the plant roots. This is why gardeners who water a lot must add nitrogen more often. If you fail to add nitrogen, what is in the plant moves to the new shoots and the older leaves turn yellow.
      Nitrogen originates from three sources. The atmosphere above us is 78 percent nitrogen, but it is unavailable to us. It makes its way to a plant's root zone by storms that carry the nutrient to the soil via rainfall. The organic matter in our soils also contains nitrogen. However, it is in a form that is unavailable to plants. It takes various microorganisms to convert it to an available form. Commercial fertilizer companies make this nutrient available by extracting it from the atmosphere and putting it in fertilizer form.
      Phosphorus is the second of the three nutrients listed on the fertilizer bag and is essential in all phases of plant growth. It is associated with increasing root growth, creating a flower show, forming fruit, hastening crop maturity, increasing disease-resistance and forming seeds. I must hasten to add that it also stimulates seed germination. That might not mean much to you at first, but if you have a lawn full of crabgrass and other weeds, the added phosphorus aids their seeds in germinating.
      You must know two facts about phosphorus to get it to work for you. First, it is stubborn and affixes to the soil. When you apply it to the soil surface, it seldom reaches the roots. Even then, the plant only uses a small percentage of the phosphorus within the growing season. The only way to ever get it down in the soil is through cultivation. You can apply it in bands below soil level, near the plant's root zone. When you plant trees and shrubs, mix it in with the soil you use to fill in around the plant.
      Second, it's also nearly impossible for plant roots to absorb in cold weather. The most common visible deficiency symptom of phosphorus is a reddish color in the lower leaves of plants. You'll see a lot of reddening of plants after the recent cold front.
      To enhance phosphorus use, choose sources that are finely ground such as bonemeal, and that are readily available, such as superphosphate, or are applied as foliar spray, such as fish emulsion. Which source you use depends on how much your plants need; give them a small amount of whichever one you choose.
      Potassium, the third element on the fertilizer bag, is essential for plant growth. You will often see it referred to as "potash." You can trace potash back to colonial days when they burned wood and other organic materials in pots to manufacture soap. They rinsed the ashes with water and allowed the water to evaporate. The residue was largely potassium. Today we mine potassium.
      Potassium functions within the plant in a number of ways. It increases the resistance of some plants to disease; and it helps plants overcome the effects of adverse weather and soil conditions. In a general way, potassium contributes to the overall vigor of plants, and it plays a role in the enzymatic process and transforms different kinds of sugars throughout the plant. Under normal growing conditions and with adequate nutrient supplies, many plants use as much potassium as they do nitrogen, which is three to four times the amount of phosphorus used.
      Learning opportunities. The Spring Flower Show featuring African violets, irises, orchids and flower designs will be held from noon to 5 p.m. Saturday and April 20 at the Nevada Garden Club Center, 3333 W. Washington Ave. For more information or if you want to exhibit flowers, call 255-1263.
      The annual Iris Show featuring many prize-winning irises will be held Saturday and April 20 at the Meadows mall, 4300 Meadows Lane, during mall hours. For further details, call 294-5059.
      "Plants For Our Climate" will be the subject of Pete Duncombe's talk at 7 p.m. Wednesday at the Desert Demonstration Garden, 3701 Alta Drive. Master Gardener Guides are sponsoring a class for children ages 5 to 10 entitled "Seed Needs" at 9 a.m. Saturday at the Desert Demonstration Garden. Parents who want their children under 5 years to attend must remain at the program with the child. Reservations are required by calling 258-3205.
     
      Linn Mills is a horticulturist for the University of Nevada Cooperative Extension.