In the News

Use Lawn Fertilizers Sparingly at Lake Tahoe
date posted: June 24 2003

Because landscape fertilizer is one of the most damaging of all pollutants to Lake Tahoe, we must be extremely careful and conservative in its use. While native and adapted plants are recommended for most of the landscape area at Tahoe because they require no fertilizer once they are established, lawns are often used as accent features close to the house, where they can add a component of defensible space. Fertilize turf just twice a year, applying only the correct amount, so excess fertilizer does not leach through the soil or run off and contaminate water in the Tahoe Basin.

Pay attention to the timing of your fertilizer application. In the spring, apply lawn fertilizer after the snowpack has melted, when the lawn begins to need irrigation. Apply fertilizer again in late August in higher, cooler locations or the first half of September in warmer sites near lake-level. This late summer application should be done when the “average daily temperature” for three or more consecutive days is below 50 degrees Fahrenheit. Add the day’s high and low temperatures and divide by two to determine the average daily temperature.

Use the correct amount of fertilizer on lawns
To determine the correct amount of fertilizer for each application, calculate the square feet of lawn by multiplying the length by the width. In many cases, it is easiest to divide the turf area up into sections that approximate a square, rectangle or triangle; then calculate the individual areas and add them up.

Select a fertilizer that contains nitrogen (N), phosphorus (P) and potassium (K) for spring fertilization. The best type contains three or four times more N than P or K. Some homeowners are experimenting with phosphorus-free fertilizers because phosphorus is one of the most damaging of lake pollutants.

Apply ½ pound to ¾ pound of actual nitrogen for every 1,000 square feet of lawn. Read the fertilizer bag label to calculate the correct amount to add. If the net weight is 20 pounds, but only 20 percent of that (4 pounds) is actual nitrogen, then it takes 5 pounds of the product to get 1 pound of actual nitrogen. Be careful of generic bag recommendations such as, “This bag will cover 3,000 square feet.” Use Tahoe’s recommended rates and calculations for best results.

A lawn that’s 40 feet by 25 feet has an area of 1,000 square feet. Each application requires ½ pound to ¾ pound of actual nitrogen. If 5 pounds of the product contain a pound of nitrogen, you should apply 2½ pounds to 3 pounds of this fertilizer twice a year.

The goal of lawn fertilization is to stimulate root growth, which is essential for controlling erosion. Using the fertilizer application rates recommended above, turf roots will take up the nutrients rapidly in late spring and again in late summer or early fall and put them to work strengthening and deepening root systems.

Because of this, conventional fast-release fertilizers such as sulfate of ammonia are acceptable for the late summer or early fall application. If applied in the fall, slow-release fertilizer pellets may remain on the turf for months, making them vulnerable to washing off slopes and into waterways during rain showers. On the other hand, if used for the spring application, slow-release fertilizers will release nutrients to the lawn throughout the summer. Since rapid spring “green-up” may not occur, homeowners should be patient, and refrain from applying extra fertilizer in the hopes of faster results.

Follow up with good irrigation

Follow up lawn fertilization immediately with good irrigation. Apply enough water to soak the ground 6 to 8 inches deep (e.g. ½ to ¾ of and inch if using a cup measurement). This washes the fertilizer off the leaves and into the root zone of the grass where it’s quickly taken up into the plant. Do not over-irrigate. This will leach (flush) the fertilizer down past the root zone and contaminate groundwater. On-off watering two or three times following a fertilizer application avoids carrying the fertilizer away in surface runoff. Compacted soils may require less time “on” and longer time “off.” Test the depth of wetness by inserting an 8 to 10–inch screwdriver into the soil. When it penetrates easily 6 to 8 inches, enough water has been applied. This is true throughout the summer.

More on fertilization
Follow the above suggestions to protect Tahoe’s water quality. In addition, avoid applying fertilizers in or near stream environment zones (SEZ) or shore-zone areas; never apply fertilizers over snow; and be careful not to overfertilize. Also, in beds and gardens and to establish ornamental and erosion-control plants, slow-release and organic fertilizers are recommended, but use them sparingly to reduce pollution. The best way to increase plant nutrients in soil is to add organic matter, such as compost, before planting takes place. More information about landscape management is available in the Home Landscaping Guide for Lake Tahoe and Vicinity. You can receive a free copy as part of a free Best Management Practices (BMP) Site Evaluation by calling the Tahoe Resource Conservation District, (530) 543-1501, Ext. 6, or the Nevada Tahoe Conservation District, (775) 586-7223, Ext. 1. You can view current fertilizer management regulations at http://www.trpa.org/fertilizerprogram/fertilizerprogram.html.

Watch for “The Lake Tahoe Report” on KOLO-TV News Channel 8 Tuesdays at 5 p.m. to learn more. Next week, learn about soil erosion and why it can cause serious environmental problems. “The Lake Tahoe Report” is a collaborative effort of the Lake Tahoe Environmental Education Coalition, University of Nevada Cooperative Extension, UC Davis and the USDA Forest Service. For more information, contact Heather Segale, University of Nevada Cooperative Extension, (775) 832-4138, or logon to www.lteec.org or www.unce.unr.edu.