Water is essential for all living things in our landscapes including our lawns, and moisture is supplied to turfgrass mainly through irrigation and rainfall. For all plants, survival is dependent on two factors: water quantity and quality. For a more in-depth explanation on turfgrass irrigation, see HGIC 1207, Watering Lawns.
The water for turfgrass growth that is supplied through irrigation and rainfall typically contains various minerals. These minerals are usually in such small quantities that they pose no problems to the lawns unless an irrigation source is contaminated. However, lawns on or near coastal regions face a potential problem from sea salt, which contains sodium chloride.
The term salt, or salinity, refers to all salts. Salts from fertilizers can contain various elements, such as calcium, magnesium, or potassium. However, high concentrations of sea salts are a concern, as they can be very detrimental to turfgrasses. High sodium levels can have a detrimental effect on the soil by displacing other elements within the soil, which can cause the soil to collapse and loose porosity. This has a negative effect on soil structure, which in turn reduces soil aeration, internal drainage, and plant growth. Coastal regions can see saltwater intrusions onto lawns through storm events and exceptionally high tides, sometimes referred to as “King Tides”. Although ocean water salinity varies on average, the salinity of ocean water is about 35 parts per thousand (ppt). Saltwater intrusion onto a lawn can have far reaching detrimental effects.
High soil salinity in a lawn can result from the use of salty irrigation water or by ocean or marsh water intrusion. Turfgrass decline and death can occur rather quickly, especially when the soil is poorly drained or without fresh water applications to flush out the salts.
Salts will reduce turfgrass health mainly through an osmotic effect. Water will move from an area of low salinity into an area of high salinity. Moisture in plant tissue contains a relatively low amount of salt. As the concentration of salt in the soil solution increases, it becomes more difficult for the plant roots to absorb water, and under extreme conditions, high salt concentration in soil can pull moisture from the plant’s root system.
The initial response of turfgrass to high soil salinity is a slowing of turfgrass growth. Leaf blades will become stiff and narrower than normal. A color change in the turf may occur, where leaf blade color becomes darker green or blue-green. Salt stressed turf may also wilt more quickly than turf not affected by salt because of the osmotic effect and the difficulty in taking up water. Turf wilting may even occur in a moist soil. Under higher salt levels, general thinning of the turf occurs as well as some leaf tip burn.
Turfgrass species vary in their tolerance to salt. Seashore paspalum is the best warm-season turfgrass for salt tolerance and may be an option where frequent saltwater intrusion occurs. Zoysiagrass, bermudagrass and St. Augustinegrass have a fairly good tolerance to saltwater intrusion; however, centipedegrass has a poor tolerance to salt. Bermudagrass lawns over seeded with ryegrass for winter color are quite tolerant of saltwater intrusion. Another aspect to salt problems in the lawn is that salt in the soil can slow or inhibit seed germination. High soil salinity can prohibit seeds from imbibing water because of the osmotic effect. Therefore, when reclaiming areas where saltwater intrusion has occurred, make sure the site is thoroughly flushed of salts before reseeding.
Reclaiming a turf site that has been affected by saltwater intrusion can be difficult and laborious. To determine what steps are needed, determine the severity that the intrusive water has caused. This can be determined by soil testing. Another factor involved with reclamation is the soil texture. Sandy soils are easier to reclaim that clay soils due to the better leaching potential in the sandy soil.
While waiting on soil test results, it is important to remove any debris, sand, or mud accumulation on the turf. Shading of the turf by debris can cause just as much damage as saltwater intrusion as it reduces photosynthesis. Remove this layer by hand raking or using a flat-headed shovel. The area should then be washed with a stream of fresh water.
Frequent flushing with fresh water is needed to flush the salts from the root zone. Again, this will be easier on a sandy soil than a poorly drained clay soil. This can be accomplished through either irrigation or rainfall. If an irrigation system pulls water from a pond or open water source, be sure the source has not been compromised by salt water as well. Water the lawn with an inch of irrigation each time. Approximately 6 inches of irrigation will flush 50 to 70% of the sodium from the soil.
To assist with the leaching and aeration in clay soils, core aerification will be beneficial. This will open the soil and allow for better drainage. The addition of gypsum (calcium sulfate) to a poorly drained clay soil may also be beneficial for soils high in sodium. If the soil is sandy and contains low levels of sodium, the addition of gypsum is not recommended. The gypsum will displace the sodium from the soil particles and allow it to be flushed through the root zone. Gypsum will work quicker when it can be incorporated into the soil; however, this may be impractical on a turf site. In this case, core aerify the soil, apply the gypsum, and water it into the soil using fresh water. Apply 50 pounds of granular gypsum per 1000 square feet monthly until a positive soil test shows that a reduction in salinity is achieved. Irrigate with one inch of water after each gypsum application.
When living on the coast, saltwater intrusion is a fact of life for most. Whether it be from a hurricane, a nor’easter or an abnormally high tide, saltwater can find its way onto a lawn. However, if proper reclamation practices are followed, turf is one of the most hardy and resilient plants in any landscape.