Choosing the Right Seed
It all starts with a seed. Before most plants can rise up out of the ground to seek the sunlight, a tiny capsule containing its DNA must be planted first.
Exactly which seeds should go where isn’t a problem for Mother Nature. In her wonderful randomness, wind and birds help her spread them around, and they find a home wherever the climate and soil suits.
For a soil erosion and hydroseeding professional, it’s not that easy.
He must choose the right seed, at the right time, for the right soil, and he can’t leave any part of that decision up to chance. Those lush green plants, whose roots are anchoring the slope beside the highway or covering the commercial project didn’t just happen.
They came about as the result of careful planning and a lot of hardwon know-how.
How do soil erosion and hydroseeding professionals go about selecting the seeds that are so vital to their work?
To find out, w e asked some experts who do this every day, under some of the most stringent and exacting parameters. They’re landscape architects who work for Departments of Transportation (DOTs) in different states around the country, specifically, Texas, Georgia and New York. They’re charged with both erosion control and beautification of their respective states’ thoroughfares.
Of course, private contractors work for DOTs as well. But even if you never work on a DOT project, it’ll be instructive to see what sort of process state landscape architects go through when choosing seed for their various projects.
Each of these states has a different climate, ecology and topography, so, it’s no surprise that each of their DOTs has a different approach to the job.
All three of the DOT landscape architects we spoke with start any project by asking some basic questions. First, they need to know what the goal is for the project—its primary mission. Is it to control erosion, or to increase the sites’ aesthetic value—or both?
The type of soil the seeds will go into is the next consideration. Is it clay, loam, or sand? Alkaline or acidic? What is the quality of that soil? Will it require amendments?
Where the site is located is probably the most critical factor of all.
Does the area receive a large amount of sunlight, or sit mostly in shade? Are there transitional zones? What are the microclimates in the area? What’s the elevation?
Planting seed that requires a lot of moisture in a dry desert environment is going to have an obvious outcome. A rocky or sandy soil in the high mountains will need plant material that can survive in that harsh environment. The climate zone of each location will determine the best type of seed to use. A warm-weather species will not be successful in a cold climate, and vice versa.
Drought is another factor. Irrigation, if any, to the site may be restricted or shut off entirely. The choice of plant species may need to be very different under drought conditions than it would be during more normal times.
The planned use of the site comes next. Will this be a high- or a lowtraffic area? Is it near a school, or any place where children or other members of the public might trample on it? Will the site be maintained or mowed?
After all these questions (and more) are answered, then and only then can the decision be made. The DOT landscape architect will choose the specific flowers, grasses, forbs, legumes, annuals, perennials, trees or shrubs that will have the best chance of survival and achieve the overall goal.
Once the type or types of seed species is decided, quality is the next consideration. A lot of variables come into play with seed.
Excellent results come only from using the highest quality seed in the best mix for any particular application.
Poor quality, substandard seed leads to spotty, unpredictable results. This will result in an expensive do-over of a project, adding additional cost to the bottom line. In a governmental project with set budgetary limits, do-overs may not be feasible. Getting it right the first time has to be a guiding principle.
You can see that a landscape architect working for a DOT has a lot to think about before even one bag of seed is purchased.
There are some other factors that go into seed choice that are more or less out of a DOT landscape architect’s control. For instance, many states are putting a stronger emphasis on the beautification of their highways and public areas.
In those cases, many grasses, plants and forbs are selected mainly for their visual appeal. Aesthetics may even trump practical considerations at times. Some areas will have multiple plantings throughout the year, to provide maximum color for each season.
The United States has a wide variety of ecologies. A single state can contain several different ones within its borders. Naturally, regional authorities within a particular state are going to differ in their concerns and requirements.
Seed selection is a project design issue. A landscape designer who works for a DOT has to know all the requirements of the project as well as the state standards. He must keep these in mind as he peruses the vast reference lists of seed from which he’ll choose.
In Georgia, the GDOT focuses on environmental concerns from the very beginning of a project. GDOT landscape architect Davie Biagi says, “We focus on environmental mitigation projects, historical mitigation projects and ornamental landscapes, in places where we want to do a more natural landscape.”
Nancy Alexander, landscape architect for the New York State DOT (NYSDOT), says her state usually allows contractors to select the seed for jobs, as long as that seed meets state specifications.
Peter Dunleavy, head of the NYS- DOT Specifications Unit and a former landscape architect, added that, “Our goal with our turf mixes is to reflect basic industry standards…to get a basic, sustainable stand of turfgrass. Depending on the fineness of the maintenance, our standard mixes are a reflection of the most common varieties found in the state.”
Georgia’s current specifications include native grasses and native herbaceous perennials and forbs. The usual mix is made from three species of the native grasses and two species out of the herbaceous forbs. It’s used on both natural landscapes and in disturbed areas, and provides a successful and reliable cover for stabilizing with native species.
Often, the mix is used in conjunction with shrubs, along with largecanopy native shade trees and native understory trees in order to create a “multitrophic” landscape, as is required by the state’s Environmental Protection Division. (A “trophic level” is an organism’s position in the food chain, i.e., herbivore, carnivore, etc. A “multitrophic” landscape provides food for more than one trophic level.)
You may have noticed the word “native” used repeatedly. All three of our landscape architects prefer to use native seed whenever possible. It makes sense; species that naturally evolved at a project site are going to do better there over time. Why not mimic what already succeeded in nature?
Native plants have already adapted to the moisture level, the climate, the elevation, and the soil type found at the location. After it’s grown in, it will usually be less expensive to maintain. Seed that has to be harvested and shipped in from a long way off will be more expensive, and may run the risk of bringing invasive pests or disease with it.
“We really have seen a big push, a big expansion of the native-seed market,” said Dennis Markwardt, landscape architect for the Texas DOT (TxDOT). “One of the things that they’re really pushing is forage production. That helps us, even though we’re not so much looking for forage production out of these plants, but rather for the soil stabilization and biodiversity that they provide. In a lot of cases, these native plants germinate and establish much easier than those that have traditionally been on the seed market.”
It seems like a no-brainer to choose natives. There is one drawback, however. While natives are usually more successful in the long run, they typically take longer to establish. If immediate, fast-growing cover is needed, they may not be the best choice. And there are other considerations as well. Markwardt says that in Texas, “We’ve really had a limited amount of native grasses available that actually perform statewide.”
There’s yet another consideration for those designing roadside projects that sometimes will preclude
the use of natives. It’s the requirement to maintain ‘clear zones.’ A ‘clear zone,’ as defined by the U.S. Federal Highways Administration, is “the total roadside border area, starting at the edge of the traveled way, available for safe use by errant vehicles.” Essentially, it’s the unobstructed shoulder, and it’s a matter of safety.
Clear zones require the use of more vigorous seed that will stabilize the soil in less than fourteen days, and tolerate regular mowing. Native tree seedlings must be prevented from establishing in these zones. Any DOT landscape architect has to think about this when deciding whether or not to use native seed along a roadway.
The state of Texas has been a pioneer in wildflower preservation and proliferation. Their native wildflowers bloom at many different times of the year. In a state as big as Texas, this can prove challenging, especially when it comes to orchestrating these picturesque blooms while balancing the year-round needs of sometimes competing fauna and flora.
“Preservation and propagation of our native wildflowers have always been the utmost on TxDOT’s list of priorities,” says Markwardt. Wildflowers set seed at certain times of the year. During those periods, the grasses that line the state’s roadsides and highways are left unmowed.
State DOT landscape architects are sometimes also tasked with creating unique outdoor spaces that will serve as havens for wildlife, while still performing the function of controlling erosion. This leads to a whole host of other things to take into account.
For instance, if it’s known that a particular species of wild hog or deer feeds on a certain clover, it’s probably not wise to plant that clover on a highway project. A plant that lures an animal close to traffic can result in dangerous and costly collisions. Accidents result in personal injury and damage to public and private property, not to mention exposing the state to lawsuits.
Whether you work for a DOT or not, any soil erosion or hydroseeding project means that the needs of the various stakeholders involved have to be weighed and measured along with the seed. There are both long- and shortterm goals to keep in mind, and at times, competing interests and agendas to juggle. Environmental and aesthetic considerations have to be harmonized with the need for effective, hopefully permanent, erosion control.