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CZ-Tip - Dune Building with Beachgrass
If you are looking for some defense against the winds, waves, and flooding that continuously batter and eat away your coastal property, American beachgrass (Ammophila breviligulata) is your plant. This hardy, salt-tolerant, native grass has strong, fast-growing underground rhizomes (root-like underground stems). The rhizomes spread beneath the sand and give rise to many new plants, helping to stabilize sands. Beachgrass also tolerates salt spray and occasional wave overwash, drying winds, low nutrients, heat, and excessive sunlight, and grows well in sandy soils, making it ideal for coastal use. But maybe the best thing about beachgrass is that it helps to develop, build, and maintain dunes.
What Dunes Can Do for You
Dunes provide a physical buffer between the sea and inland areas, helping to protect homes and properties from the damaging effects of waves, wind, storm surges, and flooding. In addition, as waves hit the dune, its sediments move and shift—a process that absorbs wave energy and protects landward areas from the full brunt of the storm. The size of the dune (the height, length, and width) determines the level of protection provided. Dunes are also sand sinks, storing sediments that shift to coastal beaches and nearshore areas when the dunes are eroded during storms. As long as the sand stays in this beach/dune/nearshore system, it continues to protect inland areas and is available to build dunes and beaches in the future.
What You Can Do for Your Dune
Whether you bolster an existing dune or build a dune from scratch, the best way to get started is to plant beachgrass. The dense root system (which runs deep and anchors the plant in place) and the fast-growing rhizomes (which spread beneath the sand and sprout many new plants) allow for quick establishment. And once established, beachgrass literally catches sand—the leaves slow the speed of wind, allowing wind-blown sand to be deposited—and this accumulation helps build up the dune. What's more, the plants thrive on being covered in sand and respond by sending out new shoots and rhizomes to continue the dune-building process. The leaves of the beachgrass also help to stabilize the dune by sheltering underlying sand from wind and rain, while the root systems help bind the sediments. And once beachgrass is established and a dune becomes more stable, other plants are able to gain a foothold, thereby creating greater diversity for wildlife habitat and reducing the potential for a loss of all vegetation to disease or pests. For information on additional beach and dune plantings to create more diversity, see the Massachusetts Office of Coastal Zone Management's (CZM) Coastal Landscaping website.
Though a U.S. Army Corps of Engineers Dune Restoration and Stabilization Study on Nauset Beach concluded that sand fences initially capture sand more rapidly than newly planted beachgrass, once established, beachgrass traps sand at a rate equivalent to sand fencing with multiple lifts (constructing additional fences higher up on the growing dune once the original fences are filled and covered by sand).
Beachgrass Planting Tips
For best results with beachgrass, here are a few useful tips:
Do You Need a Permit?
Because activities on the coast can easily impact natural resources and neighboring properties, they are consequently strictly regulated. So before doing any planting on or near a beach or dune, contact your local Conservation Commission and/or the Massachusetts Department of Environmental Protection's Water, Wastewater & Wetlands Division to determine if a permit is necessary.
When to Plant
Beachgrass grows best in cool weather and therefore typically gets its best start when planted from mid-November through mid-April (but not when the ground is frozen). You may be able to plant beachgrass a bit earlier in the fall or later in the spring (provided enough moisture is available)—but it should not be planted in the dry summer because beachgrass needs sufficient water to establish its roots. If the area to be planted is located in shorebird nesting habitat, you will want to avoid planting during nesting season—starting mid-April. Contact the Massachusetts Division of Fisheries and Wildlife's Natural Heritage and Endangered Species Program (NHESP) for additional information on wildlife and rare species management and restrictions.
Location, Location, Location
For beachgrass to thrive, it should be planted in a location with enough wind-blown sand to sustain the plantings and build the dune. Beachgrass tends to grow best when frequently covered by sand, otherwise an unhealthy build-up of thatch occurs that can harbor organisms and insects that make the plants susceptible to disease and drought.
Beachgrass should also be planted as far landward of the high tide line as feasible (most sources recommend at least 100 feet above mean high tide, if space permits). If planted too far seaward, storm tides and waves prevent vegetation from growing and sand from accumulating. Moreover, beachgrass generally grows toward the beach (i.e., toward the source of blowing sand) until the point where saltwater inundation is reached. So the farther back beachgrass is planted, the more room it has to grow, resulting in a bigger (or at least more stable) dune.
Plant Spacing and Depth
Beachgrass culms (the single plant with stem) should be spaced approximately 18 inches apart to ensure successful establishment. In areas that are particularly vulnerable to storms, waves, and washouts, plant culms closer together (e.g., 12 inches apart) to maximize sand build-up and enhance erosion control. Because the plants spread approximately 6 to 10 feet horizontally each year, there is no need to over plant.
You may also want to use a graduated density—planting culms farther apart closer to the shore to allow some sand through and then planting culms closer together through the middle and back of the dune where most sand will be collected. This arrangement mimics the natural landward-to-seaward growth of the dune and helps to prevent the dune from building up too steeply.
Whatever the density, stagger each row of plants to maximize the capture of sand and to avoid creating wind tunnels. Approximately 1-3 culms should be planted per hole at a depth of 8-10 inches. The sand should be firmly pressed down around the culms to secure them in place.
Don't forget that shorebirds start to nest in mid-April in the Northeast and planting might not be allowed at all in these areas to avoid adverse impacts. If beachgrass planting is allowed (and timed accordingly), culms are often required to be spaced 36 inches apart to allow enough open sandy areas for shorebird nesting. The Natural Heritage and Endangered Species Program can provide information on the location of endangered species habitat and any special design or permitting requirements for your area.
When beachgrass is planted at the appropriate time of year (from fall through spring), there is generally enough precipitation to sustain plantings without supplementing with additional water. Too much water will actually allow other plants to gain a foothold and out-compete beachgrass. These other plants may not survive for the long term and won't serve the same benefits as beachgrass, so it is best not to get them started.
A modest use of fertilizer can encourage plant growth and speed stem and root growth. However, fertilizers can also be washed into coastal waters where they can cause excessive algae growth, reducing oxygen supplies and leading to fish kills. The algae can also produce toxins in the water that pose health problems to people and animals.
To avoid these damaging effects, use a high nitrogen, low phosphorus, slow-release fertilizer. (See the University of New Hampshire Cooperative Extension's Slow-Release Fertilizers for Home Gardens and Landscapes factsheet [PDF, 341 KB] for details.) One application of fertilizer in the spring within 30 days of planting (but NOT before April 1) and another in late summer/early fall will benefit the growth and establishment of beachgrass. Fertilizer should not be applied too early (before April) because it will wash away before being used by the plants. Fertilizer also is not productive when applied in the mid-summer because the grass tends to slow in growth during this time. Fertilizer may actually cause die-offs of plants if used excessively, so always use sparingly (generally no more than 1 pound of nitrogen for each 1000 square-foot area that is planted with beachgrass).
Maintenance and Protection
If planted in the right location, at the right time, and under the right conditions, beachgrass plantings are generally good to go for the long term. However, you will want to protect your beachgrass from vehicular and foot traffic, not only at the time of planting, but also on well-established dunes. For all its hardiness, beachgrass cannot withstand trampling and being crushed. And once bare of vegetation, dunes are more vulnerable to erosion and blowouts. So keep your beachgrass safe and your dune stable and you will be duly rewarded with outstanding protection from storms and flooding.
For More Information
The following materials provide details on planting beachgrass and other coastal landscaping topics: