Lime may provide the key to better plant growth in sections where the soil is acidic. Therefore the gardener in such areas needs to understand how to use this indispensable material.
Plants differ widely in their tolerance to acidity in the soil. A few, such as blueberries and evergreens, will tolerate extreme acidity. However, most of our cultivated plants prefer nearly alkaline soil.
If the soil in your gardens or lawns is acidic, it will be necessary to apply lime to neutralize the acidity and grow healthy, vigorous plants partially.
The addition of lime to an acid soil will also unlock plant foods that otherwise may be unavailable to the plants; supply the essential plant foods, calcium, and magnesium; create a condition favorable to the growth and activity of beneficial soil organisms; and a limited extent, improve the soil texture.
What Makes Soil Acid?
The soil’s acidity is usually determined by the type of rocks from which the soil was originally derived.
Quartz, granite, sandstone, and shale produce acid soils. Limestone and marble are alkaline. In low areas, the presence of a high percentage of organic matter makes for acidity.
Important Factor In Soil Acidity
The amount of rainfall is another important factor in the soil’s acidity. The chemical substances capable of neutralizing acids are soluble in water.
These are dissolved in proportion to the quantity of water seeping through the soil and then carried off in the drainage water. These alkaline ions are then replaced by the acid hydrogen ions from the water, thereby increasing the soil acidity.
The removal of plant material from soil tends to make it more acidic. The tomatoes you pick, the flower stalks hauled to the dump, and the grass clippings from the lawn are all rich in alkalizing elements, which must be replaced, or the soil will gradually become more acidic.
Other Factors
Two other factors contributing to the increase of acidity in your garden and lawn soils are the continued use of acid fertilizers and the addition of organic matter, such as peat, unlimited compost, and green manure.
Determining Acidity
There is no simple way to determine the acidity or alkalinity of the soil. The presence of green moss and sour grass or sorrel in a garden or lawn is considered by many as an indication that the soil is acidic.
This is not true. And, peculiar as it may seem, the symptoms of trouble shown by a plant growing in too-acid soil may be similar to those caused by over-sweet soil.
Soil Test
The only certain answer is a soil test made by a reliable laboratory. This is an easy and simple operation.
It consists of taking a cupful of the top 6″ inches of soil from two or three places in the troublesome section, mixing them, and sending about a cupful of the mixture to your County Agent or State Agricultural Experiment Station.
Soil Testing Kits
Soil testing kits can be purchased from garden supply stores. Those testing for acidity only is inexpensive. These should be of great help in keeping tabs on the condition of the soils in your gardens and lawns.
However, I consider it very important to check the readings periodically by sending some tested soil samples to headquarters for comparison.
How Is Acidity Measured?
Terms
Such as “very” or “slightly,” used in describing soil acidity, are indefinite. Even the term “acid” may mean one thing to one person and something else to another.
A universal scale of 14 points, known as the “pH” scale, was adopted many years ago to provide a definite means of measuring the reaction of soils and other substances.
In this scale, the halfway point, or 7, is neutral. The numbers above 7 indicate the degree of alkalinity, and those below 7 the acidity.
Modern Soil Testing
Modern soil-testing laboratories use an electric pH meter to test soil reactions. This is a potentiometer calibrated to read the pH values directly. They are extremely sensitive instruments and must be frequently checked for accuracy.
Soil Testing At Home
In the test kits commonly- sold for testing soil at home, one general dye or several different and more sensitive dyes may be used to determine the soil’s reaction. Color charts are included with complete directions for use.
Trouble In Using Test Kits
Unfortunately, there are several possible sources of trouble in using these kits, such as:
- The dyes are not too stable and may deteriorate over several months.
- The color of the dye may be completely absorbed as it seeps through the soil sample.
- The chart colors may be poor to start with or fade within a few months.
- The tester must have a good eye for colors, or the reading will be wrong.
Hence my suggestion above for frequent checking of the tests you make.
What Do Plants Prefer?
You will find lists of plants with their preferred reactions in many garden books. In most cases, there will be a spread of 1 1/2 to 2 points for each plant.
In some cases, you will also find that authorities differ as much as a point or more in their recommendations.
This may be partly due to the difference in other growing conditions experienced by these gardeners. I would suggest that it only demonstrates how tolerant plants are to varying degrees of acidity.
Growing Conditions
The acid-loving or acid-tolerant plants should grow well in soils with a pH of 4 to 5.5. Most plants commonly grown in lawns and gardens prefer slightly acidic soil. Therefore, they should grow well in soils with a pH of 5.8 to 6.8.
Under average growing conditions, the so-called “lime-loving” plants, such as delphinium and others, will grow better in soil with a pH of 6.8 than in soil with a pH of 7.2. This is because the desirable plant food elements are more soluble in slightly acid soil than in slightly alkaline soil.
What Kind of Lime Is Best?
There are three types of lime commonly sold under the general terms land or agricultural lime.
Hydrated lime is a very fine, fluffy powder similar to flour in appearance and feel. It is soluble in water and gets to work immediately when spread on the soil and watered. It may contain from 60% to 80% percent active sweetening power.
Limestone
Limestone is a grayish, gritty, cement-like material consisting of finely ground lime rock. It takes time to dissolve and, as a result, is slow to get to work.
It may contain from 20% to 50% percent sweetening power, the effectiveness of which is in proportion to the fineness of the grinding.
Farm and garden supply stores commonly sell a mixture of the above two types of lime. The benefits of both are thus combined.
Over the years, there has been little difference in the effectiveness of the various types of lime when applied in equivalent quantities.
The total content of calcium and magnesium determines the “sweetening power,” so compare the percentages in the analysis, which must be on the bag or tag.
For quick results, use the slightly higher-priced hydrated lime. For the “long pull,” use the more easily applied, better keeping, and less expensive ground stone.
Is Dolomitic Lime Better?
During the past few years, soil experts have better understood the value of the so-called “trace” elements. These are plant foods, such as boron, zinc, magnesium, and others, used by plants in minute quantities but are essential for normal plant growth.
Magnesium
Magnesium is important to plants in synthesizing carbohydrates, fats, and proteins, as well as an essential constituent of chlorophyll and valuable in producing good seeds. It is deficient in many soils, particularly those that are acidic.
Dolomitic lime contains from 20% to 30% percent magnesium and 30% to 50% percent calcium and gradually replaces ordinary lime in many sections of the country.
It is available in both the hydrated and ground stone types and sells for about the same price as the old kinds. I would recommend it if it is not too difficult to obtain. You may have to go to a farm supply store to get it.
When Is Lime Applied?
As lime is most effective when thoroughly mixed with the soil, it should be applied before the land is prepared for planting.
When plowing or turning over highly acidic soil, it is best to spread lime before and after the operation, thus getting it mixed well with the soil.
If plants are already growing and the need for lime is determined, it can be spread without injury to the plants and either watered or cultivated. In such a case, the hydrated lime should give the quickest results.
Mixing With Fertilizer
Limestone can be mixed with fertilizer and then spread, or applied before or after the fertilizer, as there is practically no chemical reaction.
If it is considered desirable to use hydrated lime and fertilizer simultaneously, it will be best to apply one first and rake or harrow it in and then spread the other. In this way, the two raw materials do not come into direct contact.
How Much Is Used?
The proper amount of lime to use on a certain lawn or garden area will depend upon the degree of acidity of the soil, the texture of the soil, and the kind of plants to be grown.
If you give the proper information when sending your soil for a test, recommendations for the amount of lime to be used will accompany the test results.
Recommendation For Average Conditions
The usual recommendations for average conditions are 4 to 5 pounds of limestone or 3 to 4 pounds of hydrated lime per 100 square feet of garden or lawn.
As previously suggested, when starting a new lawn or garden in highly acidic soil or below a pH of 5.5, it is best to use two applications of these amounts, one before turning the soil and the other after.
Once the soil is up to par, or a pH of 6.3 for most plants, applying the recommended quantity of lime every 5 to 6 years should keep the soil in good condition.
Are Wood Ashes Good?
Gardeners who consider wood ashes a good source of potash seldom considers that they also contain from 4 to 10 times as much lime as potash.
As a result, they may find their soil becoming alkaline in reaction to the detriment of the plants they are trying to help.
Hardwood Ashes
The best hardwood ashes will not contain more than 8% percent potash, and the average fireplace ashes will seldom contain more than 2% percent potash.
These same ashes may contain up to 20% lime. Therefore, when you consider using wood ashes, consider their sweetening value.
They are an excellent source of lime, so use them to correct soil acidity, and you will get some valuable potash.
44659 by Paul W. Dempsey