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Thursday, November 4, 2010
18-24-6??? Understanding Fertilizer Numbers: N-P-K
Trying to determine what fertilizer to use can be an overwhelming task. Which formulation do you need for your particular situation? Should you get the bag of 18-9-9 or the bag of 5-10-5?
And what the heck do those numbers mean anyway?
It may seem intimidating, but you can figure it out. When selecting a fertilizer – whether it’s for annuals, vegetable gardens, trees and shrubs, perennials or lawns – the first question to answer is, “What analysis do I need?” The analysis is actually the three large numbers you see on every fertilizer label – put there by law – such as 10-20-10 or 10-10-10 or 18-46-0. These numbers represent the percentage (by weight) of the three major nutrients required for healthy plant growth, always in the same order: nitrogen-phosphorus-potassium (N-P-K). Each of these nutrients affects plant growth differently, and the formulation you select should depend on your specific gardening needs.
The first number is the percentage of nitrogen in the bag. So a bag of 24-8-4 has 24 percent total nitrogen. Nitrogen provides plants with the ability to produce more chlorophyll, which in turn allows plants to grow quickly. With each additional nitrogen application, plants will grow taller and develop a darker green color. So if you want a dark green lawn, use a lawn fertilizer that’s high in nitrogen – but then expect to mow more often.
The second number in the analysis is the percentage of phosphorus in the mix. For example, a bag of 24-8-4 would contain 8 percent phosphorus. Phosphorous aids in root development and increases flowering ability and bloom size. The fertilizer industry smartly markets high phosphorus fertilizer as “Bloom Booster.” High-phosphorous fertilizer should be used when plants are being established in your garden – when sowing a new lawn or planting a new tree, for instance.
The third number represents the percentage of potassium found in the product. A bag of 24-8-4 has 4 percent potassium in the mix. Potassium has many functions: It guards the plant against diseases and aids in drought protection and cold tolerance. It also serves a role in improving root development and helps in the process of photosynthesis. You might consider using a high-potassium fertilizer at the start of winter and summer to protect crops from temperature extremes or when insects and disease have caused damage to your plants.
Now, if you’re a left-brainer, you’ve probably noticed that the sum of the percentages don’t equal 100 percent. That’s because there are other nutrients and filler product in fertilizer mixtures. This filler helps to apply the nutrients evenly over an area. So no need to double-check the math.
An experienced gardener may recognize a plant’s need for fertilizer. For example, plants that are deficient in nitrogen may start turning light green or yellow. Similarly, purple foliage (on an otherwise green plant) is a telltale sign of phosphorus deficiency. The only true way to determine how much fertilizer a crop needs is to conduct a soil test. Most states offer soil samples through their Cooperative Extension Service at no charge (or for a small fee). A soil test ensures that the correct amount and type of fertilizer will be used on your plants.
Next time you’re in the garden center selecting fertilizer, don’t let the numbers on the package intimidate you. Just consider what your plants need and match their needs to the numbers. You, and your yard, will be fine!
by Daniel Overcash
How Much Water Does My Grass Need?
Obviously, this depends on the season, the grass type, and the soil type. A general rule of thumb is that your lawn should receive at least 1 inch of water per week. However, how often you water also depends on how you want you lawn to look. Many people simply do not water their lawn enough.
On the other hand, you can also water your lawn to much. Basically, your lawn needs moisture (water), nutrients, and air to grow. By watering to much, you can continuously saturate your soil to the point were the grass roots lack air and cannot grow deep enough roots. On the flip side, by not watering enough, you can dry-out the grass, soil, and root system, and your lawn may either go dormant or ultimately die during hot summer months! That's when Tim the "Yard God" next door starts giving you a hard time - if you know what I mean. Here are a few tips to keep that from happening to you:
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- The best way to gauge if your lawn is not receiving enough water is to probe the soil to see how moist or dry it is. Soil probes usually either take a sample out of the ground or use electronic sensors to test the moisture. If you're not interested in buying one of these instruments, you can simply take a narrow screw driver or stiff wire and push it into ground in several places. If you are able to penetrate to the suggested root depth (usually 6-8 inches), then your soil is properly saturated. If not, then your watering is not reaching the desired depth and you may need to water for longer periods of time (see: How Does the Soil Effect My Watering).
- You may want to perform a sprinkler test if you find that you're not getting enough water in the soil but do not know how much your sprinkler produces in a given time. A sprinkler test can be carried out by simply placing equal sized old coffee cans or containers around the area that you run your sprinkler and let it run for 20 minutes. Once completed, take a measurement of the water that has accumulated in each container. This will show you two things: One, if you are getting an equal distribution of water in the area. If not, make the necessary adjustments to your sprinkler or sprinkler heads and test again. Two, it will tell you how much water is sprayed in twenty minutes. For example, if you have accumulated 1 inch of water in your container, then you are spraying 3 inches (20 minutes X 3 = 60 minutes) of water per hour. As discussed in the soil section, the desired water amount can depend on the soil and its ability to absorb. As a rule of thumb, to reach the desired root depth (usually 6-8 inches) it generally can take sandy soils 1 hour per inch of water, clay soils 4-5 hours per inch of water, and Loam Soils up to 2 hours per one inch of water. However, this is only a general guide and it will vary for each lawn. In many cases, to reach the desired depths, clay soils will take 1 1/2 inches of water, loam soils can take 1 inch of water, and sand soils can take 1/2 an inch of water. So, depending on your soil type, make your adjustments accordingly.
- The ideal situation is to have your lawn develop a deep, healthy root system (usually 6-8 inches deep) by watering just enough (especially during the summer months) to keep your lawn nice and green. If you're unclear as to how much water is needed for your grass, your soil, or what the best time to water is, then click on each to learn more. As a general rule of thumb, you want to water more in times of high heat, lots of sunlight, high winds, dry air, and drought. Alternately, you may want to water less in times of cooler temperatures, lots of clouds or shade, low winds, humidity, and high rainfall
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