Creating a Beautiful Garden Begins With Your Knowledge of the Soil
The Three Main Types of Soil
Learn All You Can About Your Soil
People who don't garden might take soil for granted. It's something that is simply there. But a good gardener knows that the more knowledge you have about the soil around you, the better gardener you will be.
There are only three main soil types - sand, silt, and clay, all with different properties. The soil, formed over a very long period of time, is classified according to the kind of the particles of which it is made and you will find it helpful to learn as much about each kind of soil as you can. All soil consists of rock particles of different sizes along with organic matter (decayed plants, animal matter, etc). The soil is formed from the process of breaking down rocks, called weathering (physical, chemical or biological).
Rock is usually large (gravel) but in smaller sections, it is called sand. Even smaller than that is silt. Then, finally, there are very tiny pieces known as clay.
But these things are simply "starter" bits of information. Hopefully, this article will explain to you all you need to know about soil to become successful in the craft of gardening.
Clay soil is not completely made of clay and it is the type of soil about which gardeners have nightmares. In the summertime when it dries up, it can feel a lot like concrete. It is composed mainly of clay and silt particles, along with a very small amount of sand and humus (the organic component of soil). All of the particles in clay soil are small and the soil is a dark color, sometimes black.
Clay soil is fertile and highly-compacted. It is poorly aerated, has a high absorption rate of water, and drains very little. It can become very acidic. Unlike sand and silt, it is comprised of aluminum-silicate minerals that also have varying amounts of plant nutrients such as potassium, calcium, magnesium, or iron.
For most plants, you would need to add a lot of organic matter to the soil in order for it to be suitable for growing, although there are some plants that will thrive in a clay soil, depending on your location.
To determine if a soil is sandy, you can usually just feel of it. If it has a gritty texture and falls apart easily when squeezed in and then released from your hand, you can almost be sure that you have sandy soil, which is made up primarily of small bits of eroded rocks.
Sandy soil is light and drains quickly, which makes it easy to cultivate and very easy to work with in general. It warms up more quickly than clay soil but also dries out quickly and is low in plant nutrients, which are usually washed away by rain.
The soil can benefit from applications of organic matter to improve moisture retention. Amending it with well-rotted manure (fresh manure is too high in nitrogen and ammonia and can easily burn plants) or compost (including grass clippings, humus, and leaf mold) will aid in improving the soil the quickest.
Some of my personal favorites that grow well in sandy soil are sedum and lavender. There are so many different varieties of sedum available, and they are succulents so by nature, they are adapted to dry, sandy soil. Most are small groundcovers create a great look in rock gardens.
Lavender is a plant that actually requires good drainage, so it's a perfect choice for sandy soil. You can plant it in full sun and water it just long enough for its roots to become established. Then, you can forget all about them. They are drought-resistant and watering them too much will lead to their demise.
Loam is Your Goal for Soil
Loam is the ideal garden soil. It is a combination of the three soil types (less than 52% sand, 28-50 % silt, and 7-27% clay). To create loamy soil, prepare yourself for an ongoing process that involves working organic matter into the soil every year.
Creating Loamy Soil
Loam soil is suitable for growing most plant varieties and creating loamy soil should be your goal. A soil's texture, particularly its ability to retain nutrients and water are crucial, so amendments are necessary. Different-sized particles leave spaces in the soil allowing for air and water to flow. The roots of the plants feed on the minerals in the suspended water.
Decomposing organic matter creates the well-draining conditions plants need as it attracts beneficial organisms that will ensure that the soil is healthy. In order to create the desired loam soil, add organic matter such as compost, aged manure or peat moss to the area.
Organic matter, however, is used up quickly and needs to be amended each year. For most soils, you can add about a two- to three-inch layer of organic matter to the garden surface and work it into the top few inches.
Clay soils will benefit from the inclusion of sand to other organic amendments.
The Benefits of Humus to Soil
There are many ways in which soil can benefit from humus:
- It can aid in reducing soil erosion by wind or water, as it binds soil particles together into aggregates that not only will improve water intake rates but lessen runoff.
- It can improve the overall physical condition of the soil.
- It stores and supplies nutrients like nitrogen, phosphorus, and sulfur, which are released slowly and used by plant roots as organic matter decomposes.
- In sandy soil, it increases the capacity for holding water.
- The high negative charge of humus helps prevent the leaching of positively-charged nutrients. The negative charge also improves a soil's buffering capacity, or its ability to resist any changes, such as in changes of pH.
- It can stimulate the growth of beneficial soil bacteria, fungi, and earthworms.
Silt particles are too small for us to see and they have much smaller pore spaces but a lot more of them. Silt's fine particles are what give it a slippery, smooth texture, and those particles make it easy to compact silt soil. The compatibility allows it to keep nutrients and moisture in place for long periods of time, although there are plants that can cause problems for some plants. Water and air tend to have a hard time getting to the roots of plants growing in silt soil. One solution to this problem is to add compost to the top layer of silt soil.
Soil porosity refers to the pores within the soil and the porosity influences the movement of air and water. Healthy soil has many pores between and within the aggregates, whereas soils that are of poor quality have few visible pores, cracks or holes. Porosity can be affected by the way in which a soil is managed.
Silt soil is usually more fertile than other types of soil, which makes it especially good for growing crops. Silt will promote water retention and air circulation. Some plants can thrive in silt soil, such as hostas, hellebores, daffodils, and roses.
It's Important to Know Your Soil's pH Level
Soil pH always influences nutrient absorption and plant growth. Luckily, test kits for determining the pH of your soil are available at garden centers everywhere, and it's easy to do it yourself. The kits are cheap and will give you a pretty good indication of your soil's pH. If you want even more accurate results, you should send a soil sample to an analytical laboratory, which will give you a detailed analysis.
The test kit will explain to you how to take a representative sample of the soil you are testing. Always follow the directions!
How to Interpret the Results
The pH test is intended to measure soil acidity or alkalinity. A pH of 7.0 is considered to be neutral. Any pH value below 7.0 is acidic. Above a pH of 7.0 indicates that the soil is alkaline.
If your test indicates a low pH of between 3.0-5.0:
- Your soil is highly acidic, and most plant nutrients like magnesium, copper, calcium, and potassium become more soluble and wash away easily.
- Most phosphates are unavailable to plants if the soil is below pH 5.1, although some acid-tolerant plants can utilize aluminum phosphate.
- Sandy soils are often deficient in trace elements when the pH is this low.
- Fewer nutrients are available to plants because bacteria cannot rot organic matter below pH 4.7.
- What you can do: Adding lime will raise the pH to above 5.0 and help break up acidic clay soil.
If your test indicates pH 5.1-6.0
- You have acidic soil, which is usually ideal for plants like rhododendrons and camellias, which don't like lime. There may be others that I am not aware of, so always do your research.
- What you can do: If you are growing any plants other than the ones that don't like lime, you will need to add some lime to the soil.
If your test indicates pH 6.1-7.0
- Your soil is only moderately acidic and suitable for a wide range of plants.
- Within this pH range, the availability of major nutrients is at its highest. Bacterial and earthworm activity is also at an optimum level.
- What you can do: If you are lucky, and your pH falls within the range of 6.1-7.0, you do not usually need to add anything to improve the soil pH.
If your test indicates pH 7.1-8.0
- You have alkaline soil and the availability of phosphorus decreases. Plus, manganese and iron are less available, which leads to lime-induced chlorosis (loss of the green color in the leaves of plants).
- What you can do: Your goal will be to add acidifying agents in order to reduce the pH of the soil (sulfur, iron sulfate, and others).
- Note: Clay soil often requires large amounts of acidifying material. Soils with free chalk or lime are not usually treatable. If your soil froths when placed in a jar of vinegar, then it contains free calcium carbonate (chalk) or limestone and is lime-rich soil.
Need-to-Know Information on Manure
Never use fresh manure...never. It is too high in nitrogen and ammonia and will easily burn plants. It also contains bacteria that could contaminate any edible plant growing in or even near it.
Manure needs to be composted or left to rot for at least six months to a year or longer before it can be used in a garden.
If you have access to fresh manure, you could add it to a compost pile and allow it to rot on its own, but be prepared for the strong odor if you do so. A better solution would be to allow the manure to dry out and mix in or cover it with some brown composting material like dried leaves or shredded newspaper.
Questions & Answers
© 2018 Mike and Dorothy McKenney