Soil and pH

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Soil and pH

Soil texture and soil pH will influence how you use fertilizer.

Soil Texture

Soil with good texture can hold adequate water, oxygen, and nutrients for plants. Soil with poor texture won't.

You can improve the texture of any soil by mixing in organic matter such as purchased planting mixes, soil conditioner, peat moss, composted manure, or compost. To add organic matter to a bed or planting hole, mix it into the soil with a turning fork or tiller as you cultivate. You will want to use a layer at least 2 inches deep to mix into the soil; more if the ground is very hard clay or extremely sandy.

Most soils are either a porous sand or a heavy clay. In some regions, very fine silt is also common. Clay and silt pack down hard and do not drain well. Sand particles are much larger than particles of clay or silt, leaving more space for water to run through, which is why sandy soils dry out so fast. Clay soils stay waterlogged after a heavy rain.

The ideal garden soil is loamy. Which means that most of us end up having to improve at least part of the soil in our yard, especially in new neighborhoods where most of the topsoil was scraped away before building. Organic matter in the soil holds moisture yet improves drainage (figure that one out). It also increases oxygen, which is needed by roots and helps the soil store nutrients until plants are ready to use them.

Tips for Fertilizing Sandy Soil

Because of its structure, sand does not hold on to nutrients very well. Many plant nutrients dissolve in water, so they tend to leach out of sandy soil fast. For this reason, it is important to use a timed-release fertilizer that won't wash through the soil before plants can make use of it. Gardeners having sandy soils, such as are common Florida and along the coasts, often have to fertilize more than gardeners in areas such as the Midwest, which have naturally rich, loamy soils.

Sandy soil dries out quickly, so it's important to use mulch to slow down evaporation from the soil's surface.

Tips for Fertilizing Clay Soil

Clay soil has many tiny spaces that hold on to water and nutrients. Because water that holds dissolved nutrients moves through clay soil slowly, it's important to mix fertilizer into the soil well.

If you have a problem site that stays wet and packed down all the time, consider making raised beds. Besides improving the soil's drainage and texture, people are less likely to walk in clearly marked beds. Footsteps squeeze the air out of clay soil, which makes it even more hard and dense

Much of the organic matter you add to the soil will disappear within a year or two. It decomposes. This is why it is important to add organic matter each time you plant. Eventually the organic matter leaves behind humus, a rich, more lasting form of organic matter. One way to keep adding organic matter is to mulch your plants with finely ground or shredded bark. As it decomposes, it adds to the soils' organic content.

Soil pH

The subject of pH (the measure of soil acidity) often intimidates new gardeners, but it shouldn't. Soil acidity is easy to test, and problems are usually easy to correct.

Soil pH affects the ability of the soil to release the nutrients in fertilizer. If the pH level is too high or two low, nutrients can get "locked up" in the soil chemistry and become unavailable to plants.

Soil pH is measured with the numbers 1 to 10. A pH below 7 is acid. A pH above 7 is alkaline. Most plants thrive in a pH of 6 to 6.8. Check soil pH by buying a soil test kit or pH meter. You can also find out how to send soil samples to your state soil testing lab by contacting your County Extension Service.

. If needed, adjust the pH of your soil by applying lime to acidic soil or by applying sulfur or gypsum to alkaline soil. See the rates in the box to the right.

. Most plants grow well in soil with a pH between 6.0 and 6.8, but some do better if the soil pH is a little higher (cabbage family vegetables, buffalograss) or slightly lower (azaleas, centipede grass). The ideal pH of many popular garden plants is listed in the Lawn and Garden sections of this site.

. Soil pH changes slowly, but it does change. Check your soil every year or two, or more often if your plants do not grow well despite proper fertilization.


Pounds of Lime Needed to Raise Soil pH to 6.5 (lbs. per 1,000 square feet)
Soil pH	Sand	Soil Type Loam	Clay
6.0	20 lbs	35 lbs.	50 lbs.
5.5	45 lbs.	75 lbs.	100 lbs.
5.0	65 lbs.	110 lbs.	150 lbs.
4.5	80 lbs.	150 lbs.	200 lbs.
4.0	100 lbs.	175 lbs.	230 lbs.
Note: For amounts greater than 50 lbs., split into multiple treatments of 50 lbs. or less with a 2-week interval between applications.
Pounds of Sulfur Needed to Lower Soil pH to 6.5 (lbs. per 1,000 square feet)
Soil pH	Sand	Soil Type Loam	Clay
8.5	45 lbs.	55 lbs.	65 lbs.
8.0	25 lbs.	35 lbs.	45 lbs.
7.5	10 lbs.	16 lbs.	25 lbs.
Apply lime or sulfur with a drop-type spreader to avoid kicking up too much dust.

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