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Don't lime withouta soil test

November 10, 2006 1:34 am

ANSWERING QUESTIONS is part of an extension agent's job. Today I'll answer some recent questions about lawn and garden activities in November.

QWhy do you recommend soil testing? Can't we just buy lime and fertilizer and skip the soil test?

ASoil tests provide us with key information on the health and general condition of our soils. We need to think of soil as the growing medium for our turf and landscape plants. All plants have a desirable range of growing conditions. These growing conditions include an ideal pH range and nutrient requirements. A soil test tells us the soil's pH and provides information on the level of minerals or nutrients in the soil.

Soil pH measures the acidity of the soil's water. As soil pH changes, the availability of the soil's nutrients changes. To be absorbed by plant roots, the minerals or nutrients must be dissolved and in solution. Soil pH has a direct effect on the nutrients' solubility and availability. A pH range of 5.8 to 6.5 provides optimum nutrient availability to plants.

When soil pH is below 6.0, the primary plant nutrients nitrogen, phosphorus and potassium become less available to plants. In soils with a pH above 7.5, iron, manganese and phosphorus are less available.

You might note that phosphorus availability is reduced both by a pH below 6 and by a pH above 7.5. When soil pH is maintained at a level to keep phosphorous available to plants, other plant nutrients--nitrogen, potassium, calcium, magnesium, sulfur, zinc and manganese--also are highly available to the plants.

In highly acid soils (low pH), aluminum and manganese can become more available and more toxic to plants. On the other hand, soils with a low pH can have high levels of some plant nutrients that are not in solution and not available to plants. Simply adding more fertilizer does not make plant nutrients more available.

Soil pH is the key controlling factor for nutrient solubility/availability, and is second only to water as a limiting factor in successful plant growth. Lime is relatively inexpensive and the effects of a lime application last for 4 to 6 years. In managing your turf and landscape area, determining soil pH and correcting it to meet the needs of the desired plant or plants should take priority over the addition of fertilizers and other soil amendments.

A soil test is the only way to accurately determine pH and nutrient levels. A soil test cost $7, and soil test kits and directions are available from any Virginia Cooperative Extension office. These reports give very specific recommendations on lime and fertilization requirements for the type of plant to be grown. As a general rule, soil test reports can be used to guide lawn and landscape maintenance activities for two to three years.

QWhen should I apply lime?

ALime can be applied any time of the year when the ground is not frozen. The best time is fall and early winter. Lime moves slowly through the soil, and it can take months for the full benefits of a lime application to be realized. This slow movement of lime in the soil is one reason why a fall application is recommended: It allows time for the lime to move through the soil and do its neutralizing job prior to spring growth activities.

It is important to apply only the amount of lime recommended by a soil test. As I mentioned earlier, a high soil pH reduces the availability of key plant nutrients.

QIs there a difference between ground lime and pelleted lime, and which one is better?

AThe difference is primarily in the form. Lime is made by grinding or pulverizing limestone, and this manufacturing process results in the powdery form of lime. The powder, or ground, form of lime is often called ag (agricultural) lime. Lime pellets are made by combining finely ground ag lime with a cementing agent to form pellets. Both provide satisfactory results when applied correctly.

Pelleted lime is less dusty and is easily spread using a rotary or cyclone-type spreader. The pellets dissolve when they come into contact with water from rain or irrigation. When used for establishing a lawn, pelleted lime products should be spread on the soil surface and watered in prior to tilling. The watering-in dissolves the lime pellets and helps provide a more uniform distribution of lime particles in the soil. Otherwise the neutralizing activity of the pellets will be confined to zones around the pellets.

The type of spreader you use will influence the choice between ground lime or lime pellets. Ground lime is best applied with a drop-type spreader, and lime pellets work well with a rotary spreader.

Regardless of your choice, it is important to have a uniform application and avoid streaks from overapplication in some areas and missed spots in other areas. A two-step application process helps avoid the streaks and missed spots. Apply half of the lime going in one direction and the second half of the lime in a direction perpendicular to the first application. This two-step application process works well with fertilizers, too.

QCan I spread fertilizer and lime on the same day?

AAs general rule you can spread both lime and fertilizer on the same day. However, some fertilizers contain urea as a nitrogen source. Applying lime and urea-containing fertilizer at the same time will cause a loss of nitrogen due to a pH increase around the fertilizer granules. Information on the fertilizer package should include a list of nitrogen sources; it may be on the back and in smaller print. Allow three weeks between a lime application and the application of a fertilizer that contains urea as the nitrogen source.

In a case where you have urea as a nitrogen source in your fertilizer, I would apply the fertilizer first and follow that with a lime application in three weeks. For those who follow a two- or three-step lawn fertilizing plan, the lime application may need to be delayed until three weeks after the last fertilizer application.

QIs November too late to apply lawn fertilizer?

AFor fescue and other cool-season lawns, fertilizer should be applied while the lawn is actively growing. Cool-season lawns are still actively growing in November, and you can apply fertilizer. Lawns that are fertilized in the fall benefit by improved plant density and root development, and have reduced weed and summer disease problems, and higher drought and heat tolerance. Virginia Cooperative Extension recommends fall fertilization plans that can include up to three fertilizations from mid-August through November. While in some respects November is late to start on a multi-month fertilization plan, lawns can benefit from a single November fertilizer application. For lawns where a November application will be the only application of fertilizer, the sooner you can apply the fertilizer the better. For lawns that will have more than one application of fertilizer, there should be a month between applications.

In either case, the amount of fertilizer applied should provide between 1 and 1 pounds of nitrogen for each 1,000 square feet of turf.

Bermudagrass, zoysiagrass and other warm-season grasses respond best to fertilizer applications between April 1 and Aug. 15. November is outside of the optimal time to fertilize warm-season grass lawns, and no applications should be made.