Salts are common and natural constituents of all soils. Normally, these salts are present at such low levels in topsoil that plant growth is not affected. Accumulation of salts, through natural means or man’s activities, can cause plant growth problems and result in poor growth or death of plants.

Salts can accumulate to high levels in field soils that are located in low-lying and poorly drained areas. A white salt crust on the soil surface often becomes evident when these soils dry out. Using topsoil from such areas in the flower or vegetable garden should be avoided.

Salts can also accumulate in soil through improper care and management practices. Excessive fertilizing, or watering with high salt-containing waters are two of the most common ways of causing or aggravating an existing salt problem in soil. The salt content of well water should be analyzed prior to its use as an irrigation water source. It is also possible to induce a salinity problem through very heavy additions of soil amendments that have high salt content, e.g., manure, or gypsum.

Salts can become more or less permanent constituents of soil. Once the salts have accumulated, there is no chemical treatment that will remove or counteract their adverse effects on plant growth. Special management practices become necessary in order to successfully grow plants on soils with high salt content. Some recommended practices are as follows:

Digging shallow ditches or trenches to remove surface runoff water will help to reduce salt content in soil and prevent further accumulation. The runoff water will carry away dissolved salts that would otherwise be deposited on the soil surface when the soil dries out. Providing subsoil drainage through installation of perforated plastic pipe or ceramic tile is considerably more difficult and costly, but can also be used to prevent further salt build-up by intercepting and removing saline water.

Plants differ widely in their tolerance of salt. The growth of some plants may be seriously reduced when grown in soil of high salt content, while more salt tolerant plants such as beets or spinach, for example, may only be slightly affected. The relative salt tolerance of some commonly grown vegetables is shown in Table 1.

*Relative salt tolerance decreases down each column, e.g., tomato is much more salt tolerant than cucumber.

Salt content of soil can be accurately measured. Table 1 gives the salt level in soil, measured in mhos, at which a 50 percent reduction in plant growth occurs. For example, tomatoes would produce half as well in a soil having a 10 mhos test as they would in a non-saline soil (less than 1 mho). Similarly, cucumbers would do half as well in a soil having a test of only 4 mhos as in a non-saline soil.

The first and most common symptom of a salt problem is a reduced rate of plant growth. A plant growing on saline soil is smaller than normal, may have darker leaves than normal, and will wilt from drought sooner than it would in a non-saline soil. As salinity increases plant growth will cease. Leaf burn, commencing at the tip, will occur with the ultimate death of the plant.

Salts are most damaging to plants when the soil is dry. For this reason, any means of maintaining or replenishing soil moisture content will help to avoid salt damage to plants. Infrequent but heavy watering is recommended for saline soils rather than frequent, light watering. Heavy watering will help to dissolve salts and leach them down and out of the plant root zone. Incorporation of low salt containing organic matter such as peat, compost, or grass clippings will also help to reduce the injurious effects of salts because the soil will be able to hold more water, and salt concentration will thereby be diluted. High soil containing manure should not be used as an organic amendment for saline soils.

A soil test provides an accurate way of determining the amount of salt in a soil. From the soil test results and knowledge about the relative salt tolerance of plants one can then select the most suitable kind of vegetable or flower for a particular soil. Other management practices such as providing better drainage, timely watering, and addition of organic material can also be used to minimize salt injury and allow a wider range of vegetables and flowers to be grown.