In the Northwest, turf grasses and pastures are not native and even though specific seeds have been hybridized to do well in our climate, they still need help from us to grow and flourish. Soils in the Northwest are typically acidic because of soil forming factors such as the type of rock the soil comes from, topography and rainfall. To grow pasture successfully, low pH (acidic) soils need to be raised to somewhere between 5.8% and 7% throughout the root zone (top 6 to 8 inches of soil) depending on the soil and grass type. This can be accomplished through the addition of lime—something all pastures in western Washington require in order to stay productive. Adding lime should be an ongoing process every one to three years, depending on your specific conditions.
To know how much lime to use, you will need to know what the pH of your soil is, what type of soil you have and what the nutrient levels are in your soil. These questions can be answered with a standard soil test. A soil test will cost you about $10 to $40 and it will take about a week to get the results. Your test results will tell you: a) pH levels and corresponding lime requirements, b) levels of available plant nutrients, c) levels of toxic heavy metals if abnormal, and d) recommendations on nutrients needed to optimize yield. There are dozens of places where you can send in your soil to have it tested—contact your local Conservation District for a list of soil testing laboratories or visit WSU Soil Testing. We have also used the University of Massachusetts Soil Testing Lab: Common Liming Terms.
The main thing to remember is to use an agricultural lime (naturally occurring) vs. a caustic lime (a chemical compound) that can burn plants. Caustic limes are: calcium oxide, hydrated lime, and quicklime.
When do I apply? What results will I see?
Unlike fertilizers (which can actually hinder grasses when applied at the wrong time) lime can be applied anytime. Optimally, lime should be tilled into soil before planting. On existing pastures it is best to apply lime during a rainy period so it breaks down faster. You may want to rotate the areas where you apply your lime so not all pastures are tied up at once. Limestone is fairly water insoluble and will take time to break down.
When you apply lime, you may see some immediate results, such as greening. As the pH in the soil changes, nutrients such as nitrogen will become available or “released” to plants, giving them a lush, green appearance. Many nutrients get bound up in acidic soil, while plant-damaging elements like aluminum and hydrogen are more available in acidic soil. It is always more cost effective and healthier to correct pH before you determine your fertilizer needs. It is also important to choose the type of fertilizer you use wisely. Ammonium nitrogen fertilizers are one of the leading causes of creating acidic soil while organic fertilizers will help maintain a higher pH, increase microbial soil activity, reduce thatch and make nutrients more available to plants.
Although lime will not kill moss or weeds, as your soil pH becomes healthier you will notice they will be crowded out, especially if you keep your soil from becoming too compacted. Phil Marks, a Northwest seed expert and broker, suggests aerating your soil, especially in the spring before applying lime. When you aerate before spreading lime, the lime will work its way into the soil structure more easily and activate faster.
How much and how often? Where do I purchase lime? How do I apply?
Your soil test will tell you how much and what type of lime to apply while taking into consideration CEC and pH Buffer factors (learn more about these here: Soil Acidity and Liming – Part 2 or UMass Soil testing Results and Interpretation of Soil Tests). How often? As often as necessary to maintain a pH around 6.5 (something you’ll want to monitor through periodic soil testing).
Randy Akada from Wilber Ellis, a local lime wholesaler, says, “The most common mistakes people make trying to use lime and correct pH are:
- putting down all the recommended lime at once
- not getting a soil test
- over fertilizing.”
If your test recommends a high lime quantity, like two tons per acre or more, put it down in two or three batches over the course of a year.
Many feed stores such as LJC Feed sell lime by the bag under various labels such as “Dolopril” (a prilled calcium/magnesium product), “Calpril”(a calcitic lime if your soil doesn’t need magnesium) and “Dolomite” (powdered lime). Anything with a derivative of “dol” in it will have magnesium.
It is best to spread lime through some type of broadcast spreader. Drop spreaders will sometimes leave piles of lime because of the fineness of the product. A few good heavy duty tractor spreaders are shown below if you want to make a worthwhile investment that will save lots of time and labor each year:
Web sites of seeder and spreader manufacturers:
One last piece of advice is to spread lime on a calm day and to get some moisture on your lime right away!