Liming Your Lawn or Garden This Fall

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Bucket with soil and soil testing probeDoes your lawn or garden need lime? The answer to this question is a definite maybe. This is because our soils vary so much from one yard to the next. For some yards, lime needs to be added every few years to keep plants healthy.

What is Lime?

Lime is a soil amendment made by grinding limestone, a naturally occurring type of rock that is very high in calcium. Two types of lime are commonly used in lawns and gardens, agricultural lime and dolomitic lime. Agricultural lime, also sold as garden lime, is made from calcium carbonate. Dolomitic lime is made from dolomite, a type of rock very similar to limestone except it also contains magnesium. Both types of lime provide calcium for plants, but dolomitic lime also supplies magnesium, a nutrient that is also needed. Other types of lime you may find for sell include hydrated or slaked lime and quick or burnt lime. These are not recommended for lawns and gardens.

What Does Lime Do?

In addition to supplying calcium, lime makes soils less acidic. Acidic soils, referred to by old timers as sour soils, have a low soil pH. Most vegetables, fruits, and ornamental plants grow best when the pH is slightly acidic, between 5.5 and 6.5. At levels lower than this many nutrients become unavailable to plants even if they are present in the soil, while elements like aluminum become too available and can burn roots. When soil pH is too high plants may develop iron chlorosis or yellowing between the veins. If your soil pH is too low (below 5.5), most plants will not grow well no matter how much fertilizer you add. If your soil pH is already 6.5 or higher adding lime can harm plants by raising the pH too high. This makes nutrients unavailable, resulting in nutrient deficiency symptoms like yellow leaves and stunted growth. This is especially true for acid loving plants like azaleas, camellias, loropetalum, and blueberries which grow best when the pH is around 5.0-5.5.

How to Tell if Your Soil Needs Lime

The only accurate way to know if your lawn or garden needs lime is to have the soil tested. Soil test kits can be purchased at garden centers or online, but they do not provide accurate results or tell you how much lime you need to add. Fortunately, in North Carolina, there is an easy way to determine your soil pH and get recommendations for how to adjust it, through North Carolina Department of Agriculture’s soil testing lab in Raleigh. North Carolina’s soil testing lab is one of the largest and busiest in the country. To have your soil tested, collect samples from different areas of your yard. You will need to randomly collect three to five samples from each section of your yard where you grow something different, for example, 3 to 5 samples from your lawn, 3 to 5 samples from your vegetable garden, etc. Samples should be taken around 6” deep. For each sample you are going to submit (example – lawn, garden, flower bed), aim to collect a total of about a cup and a half of soil when the 3 to 5 random samples are mixed together. Boxes and forms for samples are available from NCCE-McDowell Center. Completed samples should be mailed to the soil testing lab at the address listed on the box. Samples can be submitted any time of the year and results are posted online at the Agronomic Division Public Access Laboratory (PALS). Results are usually ready within a few weeks of submitting. If your soil test results recommend that you add lime, do so the next time you plan to till the soil. Lime moves very slowly in soil naturally so needs to be mixed in to get the most benefit. In lawns or established landscape beds, pelleted lime can be applied using a fertilizer spreader.

Soil testing is FREE from April through Thanksgiving. From December through March, the cost is $4.