816 - Turf Establishment

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Turf Establishment


In the interest of economy and more efficient use of erosion control, many areas that in the past would have been covered with sod are now being treated with mulch or mulch blanket, as well as topsoil, seed and fertilizer. The amount of sod placed on each project is, therefore, minimal in most cases.

Be sure to review any special provisions for turf establishment included in the proposal.

Turf establishment that accompanies permanent erosion control should be completed as soon as possible and in all instances will be in accordance with Section 208 of the Standard Specifications for Construction.

Before turf establishment and permanent erosion control measures are begun, slopes must be dressed to plan tolerance. Plans will usually show areas requiring sod or mulch blanket. A permit to place should be issued before work begins.

In general, the following criteria apply in the application of the various permanent erosion control items.

Topsoil will be a friable loam consisting of a dark, organic, natural surface soil. Peat and muck are not to be considered topsoil.

Care should be taken when stripping topsoil to ensure the best quality material is reserved for use. In light, sandy soils the stripping should be controlled so that the thin layer of organic surface material is not unduly diluted with the sterile underlying soil.

All areas, except slopes constructed with topsoil, peat or muck, should be covered with a layer of topsoil approximately 4 inches (100 mm) thick, or as otherwise shown. After the spreading operation, all large lumps and clods are to be broken down by some effective means and stones over 2 inches (50 mm) in diameter, roots and other debris removed from the surface.

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Topsoil Surfacing, Seeding and Mulch

Prior to the seeding operation, the topsoiled surface should be lightly disked or harrowed to provide acceptable soil condition for the seed. Should seeding be delayed and the surface becomes compacted or crusted, it will be necessary to disk or harrow again.

Whenever an area is to be topsoiled, seeded, fertilized and mulched, it is desirable to pre-measure this area so the Contractor may determine amounts of materials to be placed in order to comply with the prescribed application rate. These pre-measurements should be kept in the project records to verify that application rates were reasonably close. Application rates are detailed in the specifications. Particular care should be paid to getting enough adhesive on mulch, as this is often a problem area that may result in a price adjustment on mulch when the adhesive is below the prescribed application rate.

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Experience has identified several factors that influence the establishment of turf, and these have been further proven by the turf research program conducted by MDOT and Michigan State University. The most important factor is seed bed preparation, particularly on the heavier glacial tills where finishing operations tend to compact the soil. The soil should be loose and friable, at least 3 inches (75 mm) in depth, before placing topsoil. This is necessary to permit the fine hair roots of the grass seed to penetrate the soil deep enough to establish itself. The use of a pulvimixer or other means of loosening the soil is suggested.

The quantity and quality of topsoil used is another substantial factor influencing turf establishment. Where possible, good topsoil should be salvaged and stockpiled, remembering that a 45 percent to 50 percent shrinkage will occur when it is measured out of the stockpile as topsoil surface. A good topsoil supplies humus, dormant seeds, soil microorganisms and some nutrients required for plant growth.

Stockpiles of excess topsoil may be left provided they are trimmed to present a neat appearance and do not hinder the normal flow of water.

Topsoil surface will be measured and paid for according to the item of work appearing in the contract.

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Good quality seed, selected from the Qualified Products List and meeting the required specifications, is essential for a good catch of grass. The operation of seeding must be considered important and critical. Drilling, broadcasting and hydroseeding are among the methods of sowing currently in use, with better results ensuing from the drilling method.

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Mulch may consist of straw, hay, marsh hay or mulch blanket. Hay is comparable to straw, but will lay heavier and not adhere as well. However, it contains more permanent grass seed and less cereal grains. Sodding ditches is best, as mulch will float down the ditch plugging drainage structures or culverts. In applying mulch, winds should not be so strong that control of application is impossible. Adhesive should be applied along with the mulch or immediately following. Heavier applications along the shoulder help prevent the mulch from rolling up or whipping off by traffic.

Policy requires that mulch be weighed with tickets made out in triplicate and signed by the department representatives observing the weighing. The ticket must also report the number of bales used. In some areas, where the cereal leaf beetle has infected crops, a certification of inspection by the Michigan Department of Agriculture may be required. Special Provisions will detail the requirements in such instances.

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Mulch Blanket

This mulch will be placed on areas previously topsoiled, seeded and fertilized as specified on the plans. Mulch blanket material must be selected from the Qualified Products List. The blanket rolls will be a minimum of 3 feet (1 m) wide and will be placed with the netting on top and the wood fiber against the soil. Adjacent blankets will be placed snugly against each other and stapled to the slope at approximately 32 inch (800 mm) intervals along the joints, edges and centerline of the blanket.

Staple material will be frangible (plastic) when used in areas subject to future mowing. These areas include a 20 foot (6 m) strip along the top of the foreslope adjacent to the shoulder and everywhere on urban projects. On all other areas the use of steel pins for anchoring mulch blankets will be permitted.

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Before sodding operations begin, areas will be dressed to plan tolerance. The earth beds will be thoroughly watered just before laying the sod. Sod placed in dry weather should be watered frequently as directed by the Engineer. This work is covered by the pay item Water.

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As noted in Section 917 of the Standard Specifications for Construction, the source of sod material should be an area with soils similar to the predominant soil types upon which the sod will be placed along the roadway, with exceptions as noted for sandy soils. The proper source of sod is one of the prime factors affecting successful establishment. Source fields that contain perennial grasses free from noxious weeds and that have been recently used as pasture land provide dense turf. The grazing activity accomplishes the same beneficial results as periodic mowing and fertilization. The Region Resource Analyst may be of assistance in determining the suitability of the sod field.

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The substitution of nursery grown sod in place of pasture land sod for Class B sod should not be made unless the nursery grown sod contains grass species that do not require intense lawn type maintenance. Roadside turf must be sustained without fertilizing and with limited maintenance. The bent grasses and Kentucky bluegrass are common nursery grown sods that are unsatisfactory for roadside turf due to their high maintenance requirements. Remember that the 3/4 inch (20 mm) soil thickness and soil type must also apply to nursery grown sod for Class B sod.

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After a suitable sod field is located and before actual sod lifting operations commence, the grass should be mowed to a height of 3 to 4 inches (75 to 100 mm) above the ground surface for Class B sod. Reduction of grass top growth cuts down on moisture loss between lifting and placement and also stimulates root growth, both of which are important to rapid establishment of newly place sod.

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One of the most important aspects of cutting sod is to assure the use of sharp cutting blades (so cutting is not being replaced by tearing). The minimum sizes and thickness are described in the Standard Specifications for Construction. The thickness measurement includes only the soil and roots portion of the sod.

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Transportation and handling of sod from the cutting field until it is placed on roadside areas should be conducted to retain the original soil material around the root mass. Sod should not be thrown to its final position, but chutes or pallets should be used to get it very near its final position, or it should be hand placed. Almost equally important is the retention of soil moisture in the sod being moved. Any operation that results in loss of either soil or moisture can seriously retard or prevent satisfactory sod establishment.

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Placing and Tamping

Methods of laying sod are outlined in the Standard Specifications for Construction. The sod laying operations strive to place the cut strips on the roadside area in a compact blanket similar to its original condition. The sod strips should be placed in horizontal rather than vertical rows to lessen the likelihood of washouts soon after placement. Careful placing of sod strips and tamping with a tamper designed for the purpose knits the strips to one another and also to the properly prepared soil base. This aids in erosion control and the early establishment of root growth into the soil base. Improper placing and tamping leaves voids between sod strips and a floating blanket overlay. Both conditions are deemed detrimental to satisfactory sod establishment and subject to loss by erosion.

Once the sodding operation is proceeding in a satisfactory manner, inspection is necessary only on an intermittent basis. Approximate pay quantities should be turned in daily. Sod will be final measured in place, by the square foot (square meter). Inspection should be aimed toward an “end product” or performance criteria.

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1 on 2 on slopes less than 20 feet (6 m) in height will be seeded and mulched according to methods for treating flatter slopes.

1 on 2 on slopes greater than 20 feet (6 m) in height will be set up for mulching with mulch blankets.

Slopes on the low side of superelevated pavements, with superelevations over 5 percent will be sodded to a point 12 feet (4 m) down the slope. Slopes on the low side of superelevated pavements with superelevations of 5 percent and less, and tilted pavement of two or more lanes, will be set up for mulch blankets.

All other roadside areas will be seeded and mulched, except that the following areas will continue to be sodded: selected ditch bottoms, road culvert ends adjacent to selected riprap areas, sodded spillways, fill slopes at stream crossings and where necessary in areas of potentially high erosion.

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Except as stipulated below, all slopes will have topsoil, seed, fertilizer and a mulch blanket.

For medians in boulevard sections, topsoil, seed, fertilizer and mulch with mulch blankets. Use topsoil and sod in the area between the curb and sidewalk on all projects, as well as to repair lawn areas that will be mowed by private individuals.

Use topsoil and sod around inlets and manholes outside surfaced areas, as called for on the standard plans. It is also to be used in runoff concentration areas around bridge wingwalls and retaining walls.

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Except as stipulated below, all slopes will have topsoil, seed, fertilizer and conventional mulch. As an alternate, mulch blankets may be used on selected slopes when recommended by the Region, if it is determined that conventional mulch would be less than satisfactory.

For medians in boulevard sections, topsoil, seed, fertilizer and mulch with mulch blankets. Use topsoil and sod in the area between the curb and sidewalk on all projects, as well as to repair lawn areas that will be mowed by private individuals.

Use topsoil and sod around inlets and manholes outside surfaced areas, as called for on the standard plans. It is also to be used in runoff concentration areas around bridge wingwalls and retaining walls.

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Use of Soluble and Insoluble Fertilizers

Per subsection 917.10.B each class of fertilizer is to have both water soluble and water insoluble components. Typically the water soluble and water insoluble components are packaged separately and mixed on-site, however, field staff need to be aware that at least one distributer has started supplying a 24-14-14 blend of MDOT Class A fertilizer that contains both soluble and insoluble components.

The Department has reviewed documentation supplied by distributors and have determined the 24-14-14 fertilizer blend meets the requirements for both water soluble and water insoluble components. 24-14-14 MDOT Class A fertilizer is approved for use on MDOT projects.

Additionally, there are also Class B and Class C fertilizer blends with soluble and insoluble components available that meet the Standard Specifications for Construction.

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Final Inspection

Final inspection of the work will be made by the Region Resource Analyst, accompanied by personnel from either the project or Region, and possibly representatives of the Roadside Development Unit. During final inspection, the plants will be checked for conformance with contract requirements. The marked construction plans, the inspector’s daily reports and a report similar to the end-of-establishing report (prepared after replacement planting has been completed) will fulfill the requirements of final documentation. The documents will serve as the basis for preparation of the final estimate on the project.

The final acceptance will be based on the end of each growing season report and the final report of dead and unaccepted plants, and may include plant-by-plant inspection.

The Region Resource Analyst will certify in writing that the plant materials are the species indicated in the proposal or approved substitutions. This letter will constitute the basis for the final materials certifications.

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