Want to show off your green thumb for growing outstanding vegetables, flowers, turfgrass, or other plants? Then start by ensuring that the growing conditions are right for whatever type of plants …
Want to show off your green thumb for growing outstanding vegetables, flowers, turfgrass, or other plants? Then start by ensuring that the growing conditions are right for whatever type of plants that you want to grow by collecting soil for soil samples prior to planting. The Auburn University Soil Testing Laboratory offers soil analysis services to help growers (commercial farm producers as well has home owners and home gardeners alike) make informed decisions about soil nutrients (what type of fertilizer do I need) as well as soil pH and liming recommendations on the farm or in the backyard. By supplying recommendations to help growers maintain plants and create a more sustainable growing environment, soil testing can help get spring gardens off on the right foot.
There is a very old saying that goes “Don’t be so careful to prevent ants from sneaking in the back door that you let elephants get in the front door”. This old saying does remind me of what we home gardeners often do. We spend untold amounts of money on fertilizers, chemicals, seeds, and all kinds of gardening tools and gadgets in hopes of making a successful garden. Our over-attention to such details (not that they aren’t important) often causes us to overlook a very common reason for poor yields and bad plant performance in the garden. That reason is low pH in our garden’s soil. We will gladly spend tons of money on fertilizer because we can usually apply enough of them to see growth response in our plants; we will even spend several hundred dollars on tools, tillers, etc because they are something we can use. But how many of us will spend $7 on a soil test?
Very simply stated, pH is the measure of how much acidity or alkalinity is in your soil. Soil pH is measured on a scale of 1-14 with seven being neutral, less than seven being acidic, and greater than seven being alkaline. It is absolutely impossible (no matter what anybody may tell you) to look at a soil and tell what the pH is or how much if any lime to apply. Soils are not the same and the pH can vary considerably from one spot to the next even in the same field or garden.
Most garden crops grow best in a pH of 5.8 – 6.5; however there are a few plants such as blueberries, azaleas, camellias, gardenias, and centipede grass that like a lot of acidity in the soil. These crops will require little or no liming and can have problems growing in high pH soils.
In soils with very low pH’s, common metals such as aluminum and manganese go into solution and are taken up in large amounts by plants. Taken up in large amounts, these metals can become quite toxic to plants and it is the toxicity from these two metals that actually kills many plants growing in low pH soils. We all know that clovers and other legumes do not grow well in acidic soils (this certainly includes alfalfa) mainly because the element molybdenum needed by legumes cannot be taken up. Calcium and magnesium also cannot be taken up by many plants. Finally, soil micro-organisms such as bacteria and fungi do not grow and function properly. On the other hand soil with an extremely high pH (alkaline soils) often force acid loving plants to suffer from iron deficiency because the iron in the soil does not go into solution so the plant can take it up. Azaleas, blueberries, and centipede grass are notorious for suffering from iron deficiency. For those of you who have consulted me with strange intermarginal yellowing of such plants, you will know that the first thing I recommend is not a chemical spray but rather a soil test. All plants that need a lot of iron to grow will grow better in a low pH soil. It is in this manner that your soil’s pH can partially determine what plants you can and cannot grow. Zinc and manganese deficiencies can also occur at high pH. One of the most interesting things is that nitrogen can become deficient at very high or very low pH’s, so if you’re soil’s pH is way too high or way too low it doesn’t matter how much nitrogen you put on the plants… they can’t use it! At the price nitrogen fertilizers are these days that can be quite costly as well as being detrimental to the environment.
As far as liming agents go, there are many from which to choose. Calcitic lime or agricultural lime is the old standby that we are all familiar and is the standard by which all other liming materials are measured. Dolomitic lime is now very common in both garden centers as well as farm supply stores. Dolomite lime not only benefits the soil by raising the pH but it also adds magnesium to your soil. Basic slag is an age-old liming agent (actually a byproduct of the steel industry) that is making a comeback. Basic slag offers only about ½ the liming power of agricultural or dolomitic lime, but it does offer many micronutrients not fount in other lime. Use about one and one-half times the recommended rate if you lime with basic slag. There are other liming agents as well including hydrated lime, burned lime, or even wood ashes; however, these should be used with caution as they can be very caustic when applied to living plants.
Lime may be applied at any time during the year. For gardeners, winter or early spring just prior to soil preparation is usually most convenient. Do not, however, apply caustic ashes or burned limes to actively growing plants. Ground limestone or dolomitic lime will not harm growing plants. Placement is very important to getting your money’s worth out of liming. Lime is not very soluble in water, so it will need soil contact in order to work very well. When preparing gardens, incorporate the lime to a depth of four to six inches prior to planting.
The simple task of soil testing and liming can and will save you a lot of money by reducing the amount of fertilizer you waste, by promoting healthier more nutrient efficient growing conditions for your plants, and by reducing the toxicity associated with low pH soils. Never forget that whatever it is that you are trying to grow, start by soil testing and adjusting your soil’s pH and then worry about all the other stuff.