Maintaining Historic Landscapes

What is a landscape maintenance worker’s job at an historic site? Their primary responsibility is to protect cultural resources. This would not be the first answer most people would give – however, it is the single most important part of the job. Protecting cultural resources can take the form of maintaining agricultural fields as they historically appeared, carefully trimming vegetation around historic buildings and structures so as not to damage the materials, or applying mulch to protect exposed roots of historic trees. Landscape maintenance workers are also responsible for making the site safe and attractive for visitors.

This video will answer the questions:

  • Why are historic sites maintained differently than other places?
  • What are some of the effects of poor mowing and string trimming practices?
  • What maintenance practices are appropriate at historic sites?
Oakland Plantation at Cane River Creole National Historical Park

Oakland Plantation at Cane River Creole National Historical Park

Historic sites reflect a particular time period and cultural use. These landscapes are composed of historic features such as buildings, trees, fencing, and walkways that date to an historic period. Understanding and implementing appropriate maintenance practices to preserve a site’s historic character and its individual features are essential components of a maintenance worker’s job.

There are two broad categories of landscape features at historic sites: built features and vegetation. Both are subject to damage due to inappropriate or careless lawn mowing, string trimming, herbicide application, and other maintenance practices.

Examples of damage to built features include chips, cracks, dislodged material, scarring from string trimmers, and salt residue. These types of problems are not unique to historic sites; however the age of historic features makes them more susceptible to damage.

Damage to a mature tree.

Damage to a mature tree.

Trees can also be damaged from careless lawn mowing and string trimming. Cutting, scratching, removing, or scarring tree bark or roots can result in parts of a tree dying, insect infestation, limb weakness, or disease. Older trees are particularly sensitive to mechanical injuries because they heal slower. The effects of damage on tree health may not be visible immediately, but can impact a tree over time and shorten its life. Loss of a mature tree can significantly alter the character of an historic site.

Appropriate Maintenance

Mowing is one of the most time-consuming maintenance jobs at most historic sites. It can also be one of the most destructive practices if it is not done carefully. There are several ways to avoid contacting structures and trees with lawn care equipment, including:

  • Creating a non-mow protective perimeter around features
  • Attaching protective bumpers to the lawn mower
  • Raising mower blades to avoid low-lying features, and
  • Using smaller machines in small spaces
One way to create a protective perimeter is to use mulch around the base of a tree or in flower beds. Not only will mulch protect these features, it can also inhibit grass and weed growth; help retain moisture; cool soil in summer and keep it warm in winter; and improve soil drainage.
One way to create a protective perimeter is to use mulch around the base of a tree or in flower beds. Not only will mulch protect these features, it can also inhibit grass and weed growth; help retain moisture; cool soil in summer and keep it warm in winter; and improve soil drainage.

One way to create a protective perimeter is to use mulch around the base of a tree or in flower beds. Not only will mulch protect these features, it can also inhibit grass and weed growth; help retain moisture; cool soil in summer and keep it warm in winter; and improve soil drainage.

Use natural mulch such as shredded wood or pine needles. Select the mulch carefully. Do not use bark or wood chips from diseased trees, or mulch from trees that naturally inhibit plant growth, such as black walnut. Pine needle mulch is a good choice, but use with caution because it can acidify soil. Do not use mulch that includes weed or grass seeds, as they will grow in the mulched area.

Lay the mulch to the drip line of the tree or boundary of large root areas if possible. Mulch should be 2”- 4” deep and about 6 inches AWAY from a tree’s trunk. The mulch will decompose and will need to be replenished periodically, maybe once a year. If there is too little mulch, usually less than 2 inches, grass and weeds will begin to grow.

A mulch "volcano" should be avoided.

A mulch "volcano" should be avoided.

Avoid creating a “mulch volcano,” which is a large mound of mulch around the base of a tree. Over mulching may retain too much moisture and cause root rot; stress trunk tissue which leads to insect and disease problems; prevent water and air from reaching a tree’s roots; and create habitat for rodents which may damage the tree by eating the bark. Mulch should not be applied around the perimeter of an historic structure because the organic material retains moisture and can serve as a food source for termites or other unwanted organisms.

Using an herbicide to control weeds at the base of an historic feature will also create a protective perimeter between the feature and a lawn mower. While sometimes a good option, using herbicides can potentially damage built features. Herbicides should not be used to create a protective perimeter around the base of a tree or along exposed tree roots because herbicides can harm trees.

Herbicide salt crystals on a brick sample

Herbicide salt crystals on a brick sample

Even with careful application, herbicide spray rarely is confined to the intended target. Spray on historic stone and masonry can cause long term damage to the material. Herbicides contain salts, and when absorbed into the stone, form crystals that expand. These crystals, called efflorescence, can appear as a powder or white line on the surface of historic materials. Pressure from the growing crystals can physically damage the historic brick and stone.

Herbicides applied directly to the ground can also be absorbed by brick and stone.

Using herbicides can alter the appearance of a landscape. A typical use is around the base of gravestones in cemeteries. While it may be a time saving choice, compared to weekly string trimming, the result detracts from the landscape’s historic character.

If you choose to use an herbicide, use the least amount necessary and apply with care. Do not apply on a windy day, as herbicide may hit unintended targets. Consider adding a temporary, water-soluable dye to the herbicide, which will help to show exactly what the spray hits unintentionally.

Planting ground cover around a feature can create a protective perimeter.

Planting ground cover around a feature can create a protective perimeter.

Planting ground cover around a feature can create a protective perimeter between historic features and mechanical equipment. Some ground covers can grow over tree roots and inhibit weed growth, eliminating the need to mow or trim under the tree canopy. Remember to choose the right plant for the location: use shade-tolerant ground covers under trees with dense canopies and plants that can tolerate full sun in bright, open locations. Avoid using invasive or aggressive ground covers that may grow beyond the intended location.

Another way to minimize contact damage between upright historic features and riding lawnmowers is to attach a soft bumper to the mower. Everyday items can be used to create bumpers. Swimming floatation tubes can be cut lengthwise and attached to the mower using zip ties. Other soft materials, like pipe insulation and boat dock bumpers, can also be used.

To make and install a bumper, you will need a few tools. You need the soft bumper material, safety goggles, a drill, a drill bit capable of drilling through the metal, zip ties, and a utility knife. First, drill holes through the mower blade cover, about 6-8 inches apart. Measure the length of the blade cover requiring a bumper and cut the soft bumper material to fit. If the bumper material is not already scored lengthwise, make that cut. Open up the cut and place the soft bumper material around the edge of the blade cover. Secure the bumper in place on the mower with the zip ties. Be sure that the bumper does not interfere with wheels or other mechanical part of the mower.

At times mowing over exposed tree roots or other low lying features is unavoidable. Minimize damage by raising the mower deck so the blades do not contact the historic feature. On most commercial riding lawnmowers the blade height can be changed without dismounting from the mower. Simply slow down, depress the foot petal before reaching the low lying element, slowly pass over the feature, and then lower the blade to the original position. Taking a bit of time to raise the mower deck can prevent damage to a tree, grave marker, or other low lying historic feature.

Be sure bumper does not interfere with machine parts.

Be sure bumper does not interfere with machine parts.

Large riding mowers are great time-saving machines. Their size, however, may not be compatible with historic landscapes which were originally mowed with smallerpush lawnmowers or were trimmed by livestock. For small spaces where contact between a large riding mower and an historic feature is almost certain, using a smaller lawn mower or string trimmer is recommended. Though pushing a smaller mower will take more time, it is easier to avoid hitting, chipping, cracking, or otherwise damaging closely spaced historic elements.

Loose lawn clippings can be harmful to both historic and mechanical equipment at historic sites. Decomposing clippings can cause decay at the base of wooden structures. Clippings can interfere with mechanical equipment function, such as air conditioner compressors. When mowing, plan a path so that the lawn mower blows the clippings away from buildings, equipment, and other features. If directing clippings away from historic structures or other sensitive features is unavoidable, be sure to remove the clippings after mowing by sweeping, raking or using a blower. Be careful not to remove historic materials, such as loose mortar or wood, from an historic structure when cleaning up grass clippings.

Simply slow down, depress the foot petal before reaching the low lying element, slowly pass over the feature, and then lower the blade to the original position.

Simply slow down, depress the foot petal before reaching the low lying element, slowly pass over the feature, and then lower the blade to the original position.

String trimmers are effective for cutting vegetation in areas that mowers cannot reach, but trimmers can easily strike and damage historic features. Scars and scratches on features such as headstones and trees are the most common types of damage.

String line comes in a variety of shapes and diameters. A thicker string may last longer, but it can do more damage. We recommend using a round line with a smaller diameter. Thinner string may break more freely, but it will do less damage if it comes in contact with an historic built or vegetative feature. Breaking can also signal that something other than grass or weeds are being hit.

Take care when operating a string trimmer to avoid contacting unintended targets The guard can be used to protect both the operator and the feature from the string line. If the string breaks, take a minute to figure out why. Did the string hit a hard surface? Was there something hidden in the vegetation? Or did it break due to normal wear and tear?

Protecting cultural and historic resources is the primary responsibility of maintenance workers at historic sites. Historic buildings, structures, and vegetation at these sites are irreplaceable resources and great care must be taken when working around them. We hope this video has been helpful by showing landscape maintenance techniques for historic sites.

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