For a society that demands instant gratification, sod is to turfgrass what a DSL line is to your computer: finished visual images come real fast. Not perfect for every installation or renovation, sod still reigns as the premier way to add turfgrass to any landscape situation.
IS SOD WHAT YOU NEED?
If yours is an initial use of sod, there's a simple way to choose the best turfgrass form for your use. Visit the Web site for Turf Producers International (TPI) at www.lawninstitute.com. Once you've found the home page, click on “Turf Resource Center”, and then click on “What's best for me?” A simple test will help guide you in your selection of sod versus seeding or hydroseeding. Sprigging, a planting form used with warm-season grasses, is not incorporated as an option.
Before the mechanical equipment rolls in to prepare a seedbed for turfgrass sod plantings, the enlightened grounds maintenance manager has already spent hours of time preparing for a successful project. Before the first ripper teeth hit the soil surface, a well orchestrated turfgrass planting should have already been effectively worked out. If you've chosen sod, here's a checklist on how to improve the quality and longevity of the installation.
SELECTING THE RIGHT TURFGRASS
Before the specifications can be written for sod selection, you need to select a good turfgrass mixture. Will the turfgrass stand be used as a playing field, park open space or in an un-trafficked entry area in front of a corporate office building? Each one of these specific uses demands the proper selection of suitable turfgrasses.
Selecting an appropriate turfgrass for sod could be done a couple of different ways. First, you could call your region's sod farms to see what varieties are available and then research the characteristics of the turfgrass species used for the sod. Or, you could use the TPI Web site listed on page 32 and once you've gotten to the “Turf Resource Page,” click on “The Basic Grasses” to find out what's available in sod. The checklist below will also help you make your selection.
- Test your soils
Soils for future turfgrass areas should be tested minimally for pH, macro- and micro-nutrients and for soil texture (the relative proportions of sand, silt and clay and organic matter.) You should also examine soils for depth and determination of relative soil horizons: the ‘A’ (topsoil) horizons and ‘B’ (sub-soil) horizons. You can reach these through the use of a backhoe, if one is on site, or by using a shovel or soil auger.
- Knowing the fertility
Mechanical aspects and depth of the soils you're working in will enable you to determine what soil amendments might be necessary to produce the best turf possible.
- Evaluate other micro-climatic considerations
Are there prevailing winds, areas of sun and shade and different soil types in the area that you will install the turfgrass sod? Knowing your micro climatic differences can help you plan for the best turfgrass selections. Using slightly modified different seed mixes for sun and shade areas, or knowing where two soil types interface will help you better determine the correct turfgrass and irrigation systems to use.
- Plan your irrigation systems well
In most large turfgrass areas, some form of rotor irrigation head, capable of throwing greater distances is practical and efficient whereas smaller areas will most likely be irrigated by spray heads. You should also evaluate development of sub-surface irrigation systems for each individual turfgrass installation. Remember that turf in shade and turf in sun have different irrigation needs. Water each related sun area with a different irrigation circuit, one whose run time on the controller can be more exactly tailored to water needs.
- Consider the grading and drainage implications
Turf areas should be designed with smooth flowing surfaces, with minimum 2-percent slopes and good, long-distance transitions between flat and steep portions. As you are preparing the seedbed areas, consider the mounds, berms and hills as forms of elevation changes within turfgrass areas. Also, slopes deserve much essential consideration. Slopes should never be steeper than is acceptable for safe mowing practices, and irrigation should always go across the slope. Top, middle and lower irrigation heads should be individually circuited.
- Plan for equipment access and verify property lines
A commonly overlooked factor in the installation of a large turfgrass sod area is equipment access. Before starting a project, figure out your dump truck and general equipment dimension requirements. Although a larger piece of equipment may be more useful on a particular project, if access is difficult you may have to use a smaller piece of equipment, even if it is less efficient. Make a thorough evaluation of property lines prior to starting a project. If any access routes or property lines are in question, contact a land surveyor to carefully stake out those specific lines and boundaries.
PREPARING THE SEEDBED
Seedbed preparation varies greatly from project to project, and the use of specific seedbed preparation equipment will depend on the scale and complexity of the job. Listed below is the process that would most likely be followed from the most complex project to the least complex. In chronological order, these required tasks would be:
Remove existing vegetation. If the site is heavily wooded, you will need to remove trees, shrubs and other vegetation before sod installation. Whereas shrubs and herbaceous materials are easy enough to remove and dispose of, trees and their roots are another matter. Once you cut a tree as close to the ground surface as is possible, then you should remove the stump. Depending on the size of the tree, it may be necessary to remove the stump with a backhoe, and then to additionally grub out large diameter roots. The extent of grubbing for the removal of tree roots will depend on each individual site. It is important to remember that large tree roots should be removed if they are within a foot or two of the surface, as subsequent decomposition of the roots will cause the soil surface to settle.
Remove large rocks, boulders and other impediments. If the site is rocky, it is important to remove large boulders and rocks (of roughly more than 1 foot in diameter) using mechanical equipment such as a backhoe or front-end loader. Once you have removed the large rocks, begin removing the small ones with a rake towed behind a tractor in subsequent finish grading operations.
Rough grading. If extensive grading is required, a grading plan should be prepared by the project landscape architect or engineer. Related to the grading plan will be the total quantity of soil to be removed or replaced. For extensive cuts, figure out how much, if any, of the cut material can be stock piled on-site for subsequent reuse. The soils report and testing should indicate the nature of the subsoil. The respective subsoil preparation (such as scarification) should be specified. At this point, you should also rake the surface of the soil to a depth of ideally 6 inches to 1 foot to remove any foreign objects or rocks. from the immediate soil surface.
Placing topsoil. If extensive grading is required, and especially if fill soils are required, make sure the fill soil has been tested for related fertility and mechanical qualities prior to placement. It is best to require the results of that soil testing from the soils provider in writing. If you have stockpiled site topsoils, replace them at this point. Place topsoil in no greater than 1-foot-thick lifts and redensified under the observation of the project engineer.
Trenching for irrigation systems. There are two general ways of trenching for irrigation systems related to the turfgrass: One is to trench during rough grading; the other is to trench after finished grading. The benefit of trenching during rough grading is that the subsoils are brought to the surface and are subsequently amended during incorporation of organic matter and amendments. The downside is that if irrigation laterals and standpipes are plumbed prior to finished grade, they can sometimes be broken during rototilling operations. If trenching is done after finish grading, the offset is that subsoils are brought to the surface and can be notably different than amended soils. These subsoils can be problematic in terms of the uniform growth of turfgrass at the soil surface.
Soil amendment and incorporation of organic matter. Depending on the results of the soil chemical and physical analyses, you should amend the soil at this point. Amendment of the soil might include the incorporation of soil nutrients; chemical amendments such as lime, sulfur and gypsum; and the incorporation of organic matter. Do not be surprised at the change of soil volume; incorporation of organic matter and soil amendments also incorporates air into the soil, and the soil may appear more voluminous than desired. After the finish grading and rolling, and following a few irrigations, the soil will gradually settle down to the planned grade.
Finish grading and rolling. Once you have amended the soil as per the specifications, the next step is to smooth out the soil surface and to slightly compact it. If necessary, rake the soil to remove smaller stones and roots. At this point, you have finally achieved the surface necessary for the installation of sod.
Installation of gopher wire. In many regions, gophers, voles, moles and ground squirrels can ruin an otherwise perfect sod installation with their burrowing. Manufacturers have developed special hardware cloth and wire to anticipate the different sizes of vertebrate species that burrow in the soil.
Install gopher wire directly on top of the finished rolled soil. In order for the wire to fit snugly to the soil, which enhances immediate root contact between the soil and the sod, insert metal erosion control netting staples, available at most landscape suppliers. Install staples in a triangular spacing. In sandy, loose soils use longer staples (9 inches or longer); in thicker clay and silt soils, shorter staples (6 inches or less) work better. You may need to pre-irrigate thicker soil no closer than two days before sod installation to soften the soil for easier stapling. The goal of pre-irrigation is to soften the soil for the staples and not over-water and negatively affect the installation of the sod on muddy soils.
Sod installation techniques: Sod comes in rolls designed to be laid like carpet and rolled with equipment that expels trapped air and creates a better soil interface for effective rooting. Whereas sod for residential and commercial use measures approximately 1.5 feet by 6 feet per roll, newer “big-roll” sod makes installation of turfgrass areas a less labor-intensive task. Check with local sod farms to make sure they cut big-rolls before planning their use.
Knitting edges and rolling. To avoid the new sod drying out, and especially to prevent the introduction of weed species, it is important that the ends and edges of the sod rolls be “knitted” together to provide adequate joining of the seams. It is acceptable for the seams to overlap slightly as rolling with a lawn roller will help knit them effectively.
Fertilizing as per manufacturer's specifications. Depending on the turfgrass blend, the grower may recommend fertilization before, during or after the installation. If you have the results of a site soil sample available, pass them on to the grower before a fertilizer recommendation is made; your soil chemistry or texture may influence the type and composition of the fertilizer.
Irrigating sod during and after installation. As you'll see, sod rolls on large installations can dry out during installation, both on the palette and on the soil surface. On those warmer days remember to use a fine spray nozzle to lightly wet the soil surface as the sod is rolled out and lightly wet (or tarp cover) rolls on the palettes to prevent drying out. Once the rolls are laid out in specific areas, soak the sod and soil beneath it to slightly below the root depth of the sod. Avoid walking on these soaked areas as footprints can create permanent low-spots if the soil is too wet.
BE PATIENT AND ‘KEEP OFF THE GRASS’
Sod growers and installers agree that three weeks is an accepted minimum for sod establishment, although most agree that two weeks is the bare minimum. This is dependent on temperature, water, soil conditions and intensity.
David Downey is the parks division supervisor for the coastal community of Capitola, Calif. As happens in most coastal cities around the world, Capitola is inundated with tourists during the summer. The more tourists, the more lawn traffic. Because Capitola has been largely built out, most of Downey's work with sod has to do with turfgrass renovation and repair. His greatest challenges are with summer repairs and related sod installations. Despite marking cones and flagging, pedestrians walk right through them. These repair areas never get enough time to effectively root. Downey admits that, despite the disturbance during rooting with sod, the same phenomenon would happen with a seeded area, and even worse: they could also yield the unwanted addition of mud to sidewalk. At least sod is still attractive the day it's rolled out.
Downey has had a peripheral challenge with the plastic netting that is used to hold sod rolls together. If sod is used to repair play fields, soccer spikes can snag the plastic netting, pieces of which have actually blocked area drains.
Bruce Moncrief is a sales representative at Greenfield's Turf, Inc., located in the Salinas Valley of California. Regarding Downey's experiences with problems related to the use of nylon mesh in sod production, Bruce's response is that the verticutting and aerating processes, described below, are essential to breaking down the mesh effectively enough that it doesn't snag on sports shoes with cleats. If there is enough lead-time, non-netted sod can be grown to meet the specific needs of a project.
After the initial establishment, follow the sod grower's maintenance recommendations. Mow often, removing no more than ⅓ of the grass height at a single mowing. Keep your mower blade sharp. Use local TPI mowing recommendations for your type of lawn by visiting their Web site, www.lawninstitute.com.
Fertilizer and chemical applications will depend on climate, sod type, soil, insects, weed and disease conditions. Again, follow your sod grower's recommendations whenever possible.
Depending on the wear-and-tear a sod installation receives, it may need additional mechanical treatments to improve its health. Verticutting removes thatch that has built up during the mowing process. This organic mat, if it becomes too thick, can prevent irrigation water from reaching the root zone of the sod, as well as acting as a breeding area for pests and diseases. Once thatch has been laid up on the surface of the turfgrass, it should be raked up and recycled, if possible, or removed to a landfill for disposal. Fertilization and deep irrigation generally follow the verticutting process.
Depending on the amount of foot traffic and play turfgrass receives, the soil beneath it, especially heavier soils, will become compacted and drain poorly. Generally, irrigation water will run off instead of percolating into the turfgrass' root zone.
Through the use of different types of machinery, remove plugs of sod and soil through aeration. You can either rake or sweep up the plugs for removal or leave them on the surface where they will decompose relatively quickly with regular turfgrass irrigation.
If the sod is weed-free on delivery, and if the seams between rolls are tightly knitted, post-emergent weed treatment is greatly diminished. Most of all, sod's immediate, fully mature look and shortest establishment time make it worth considering despite its initial costs.
Steve McGuirk is a California licensed landscape architect, living and working in the Monterey Bay area.
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