Hillside Greenhouse

Soils

Plants rely on good soil for moisture and nutrients. Knowing some basic information about your soil is essential for you to care for your plants and keep them healthy.

Let's consider three main characteristics of soil.

1. Soil Texture
2. Soil Structure
3. Soil Fertility

Soil Texture

Soil texture describes the particle size distribution of the soil. Soil is composed of three main particle sizes -- sand, silt, and clay. Sand is the largest particle and clay is the smallest. The distribution of particle sizes in the soil affects both the soils fertility and water holding capacity.

Soil texture can have a strong influence of the soil's moisture holding capacity. If your soil is very sandy, it will not hold a lot of moisture and you may have to irrigate more during dry weather. If your soil has a lot of clay, it can hold a great deal of water and you will have to be very careful not to over-water which may result in root rot.

Here is a quick test you can do to determine what kind of soil you have. The soil needs to be moist for the test to work. If the soil is dry, water it down and wait about an hour before doing the test. Pick up a good fistful of moist soil. If it is full of rocks throw those out and get a fistful of mostly pure soil. Give it a good squeeze. If the soil forms a ball that is fragile and can be easily broken apart into chunks, you have pretty well blended soil. If the soil will not form a ball it is quite sandy. In this case, if you rub some of the soil between hour fingers, you should be able to feel the sand particals. Finally, take some of the soil between your finger and thumb and try to form a ribbon. If you can do that, your soil contains a lot of clay.

Soil can nearly always be improved by the addition of organic matter. Organic matter will make sandy soils hold more water and will help clay soils drain better. Organic matter holds nutrients and releases them slowly for the plants can use them. Organic matter can be purchased in the form of peat moss, composted manure, or even composted yard waste. You can also obtain it for free by composting your own yard waste. Even if you have pretty good soil, it never hurts to add more organic matter.

Most plants grow best in soil that is well drained, but moist. That means the soil holds water, but there is still a lot of air space between the soil particles. Here is a very simple test to help determine if your soil is well enough drained. Dig a hole about a foot deep. Fill the hole with water. If it doesn't drain out within about two hours, you probably have poorly drained soil. If when you first dig the hole, you find water seeping in, you have a high water table and may have difficulty growing plants without some major modifications.

Poorly drained soil can be improved by addition of organic matter, but sometimes the soil is so bad, or the water table is so high, that you have to build a raised bed. This involves bringing in enough good soil to build a mound. The mound can be free standing or better yet, it can be held in place with some kind of short retaining wall made from boards, landscape timbers, or masonry. This kind of structure helps water to drain from the raised bed and keep the plant roots healthy.

Soil Structure

Soil has a second physical characteristic that we call structure. Structure is the physical way that the soil particles bind together. Soil with good structure is open to the flow of both water and air. Even a soil that contains a large amount of clay can develop a structure that allows adequate drainage. Structure develops over time based on the chemistry of the soil and the physical conditions that act upon the soil. For example, a soil that has good structure can be damaged by being driven on when wet. This excess force on wet soil can cause the soil particles to be pressed together, collapsing and damaging the structure. Be especially careful when working with wet soil so that you don't cause compaction.

Most garden plants will do best if planted in soil that has been turned over and broken up. This can be done with a spade or shovel, or by using a garden tiller or some other power equipment. This opens up the pores of the soil and allows for better air and water flow while also helping to remove weeds. It also gives you a chance to work organic matter, fertilizer, etc. into the soil. If possible, the soil should be "worked up" before planting each year. Be careful around existing trees, shrubs, and perennials so that you don't do excessive damage their root systems.

A garden tiller, if used when the soil is wet, may actually break up the soil too much and possibly damage the soil structure. A tiller is a huge labor saver and it's use, when you have a large area to work, outweighs the damage that might occur. If you use a tiller, it's especially important not to walk on the soil too much when it's wet. Walking or driving on loose soil when it's wet can cause excessive compaction and result in reduced air and water flow through the soil.

If you have a bed full of perennials, working the soil up each year isn't possible. Therefore it's especially important to have the soil in good condition before planting perennials.

Soil Fertility

It's difficut to assess a soils fertility just by looking at it. If it has adequate organic matter and you are applying some fertilizer each year, the soil probably has adequate fertility. In areas where you are growing flowers or vegetables, you can generally be safe by adding about one tenth pound of nitrogen per 100 square feet each year. If you buy a 10-10-10 general purpose fertilizer, this amounts to about a pound of actual fertilizer per one hundred square feet. (A hundred square feet is equal to an area that is about 10 feet by 10 feet.)

You can judge your soil's fertility to some degree by observing how the plants grow. If they grow at an adequate rate and have green, healthy looking foliage, there is sufficient fertilizer. Stunted, yellow plants indicate too low of fertility. If plants are fast growing and a lush, green color, but do not flower much there may be an excess of fertilizer.

The best way to know exactly how much fertilizer your soil needs is to have it tested. You can buy home testing kits, or better yet, have it tested at the University Soils Lab. The link below gives more information.

The University of Minnesota Soil Lab offers soil testing services for businesses and homeowners.

Growing plants in containers restricts the amount of soil available to the roots and as a result, also reduces the amount of fertilizer available to the plant. When planting pots, it's usually best to include some slow release fertilizer in the soil so the that plants won't run low before fall. Even then, some vigorous plants in small containers may need additional fertilizer during the growing season. This is most easily applied as a liquid fertilizer along with the irrigation water. Hanging baskets can often run low of fertilizer and need a boost. Even if the basket was planted with slow release fertilizer, it may need extra water soluble fertilizer as often as every 2 to 3 weeks.

Purchasing Soil Mixes

You can buy a number of different types of soil mixes for your containers. Most of them will provide good conditions for plant growth.

Good soils will often be blended from:

• Sphagnum peat moss
• Peat
• Perlite
• Vermiculite
• Composted pine bark

Be wary of soils that contain large amounts of peat that aren't labeled as sphagnum peat or large amounts of generic compost. This may indicate the soil contains large proportions of material that don't provide good drainage.