Roadside redo


POSTED: Sunday, February 08, 2009

Question: I lived on a hillside a while back, and nothing would grow there that had to be watered. So I planted some cactus plants, low ground-hugging plants with pink flowers. They survived in a barren and waterless situation. Why can't the state Department of Transportation (DOT) plant something like that in the H-1 and H-2 areas that was written about (”;Kokua Line,”; Jan. 14)?

Answer: The DOT did consider using the “;ice plant”; you refer to (genus Carpobrotus).

Luckily, state officials were able to learn from the experiences of the California Department of Transportation, which had used the succulent along its roadsides.

The plant, originally from South Africa, proved to be highly invasive, forcing CalTrans to spend millions of dollars removing it, said Christopher Dacus, landscape architect with the DOT's Highways Division Design Branch.

Generally, the succulents and cactuses considered for use along state roadways do poorly when it comes to preventing erosion, he said.

However, the future of the barren roadsides is not necessarily bleak.

Think native plants.

The DOT has been working with University of Hawaii professor Joseph DeFrank, a specialist in weed science and vegetable ornamental crops, to find an effective ground cover for bare areas along state roadways.

In particular, the research is targeting native plants to be used for new roadside construction projects (which includes existing roadways that are “;rehabilitated”;).


We recently visited the approximate 1.5-acre site adjacent to University Avenue and the H-1 freeway offramp to Manoa where DeFrank, with the UH Department of Tropical Plant and Soil Sciences, and Orville Baldos, a graduate student in the department, are working on the “;Native Hydroseed Experiment for Future DOT Roadside Projects.”;

It took a lot of manual labor to clear the area of weeds and overgrowth to get it to the almost barren landscape for replanting.

Now there are patches where the native Mau'u aki aki sedge, a grasslike plant, is thriving, and areas where the more ornamental emoloa grass is sprouting.

There's still more planting to be done, but in a few months the area should be awash in green, Baldos said.

The normally unused area, owned by the DOT, reflects the low-rainfall conditions and terrain typical along state roads, Dacus said.

The research being done will produce a base of knowledge now nonexistent about how the natives can be used as cost-effective ground covers, Baldos said.

While native plants have been widely used for years along roadways on the mainland, it's only recently being done in Hawaii, he said.

Weed control is a key focus of the research. So is developing a protocol for harvesting the seeds and hydroseeding, DeFrank said.

The emoloa grass is not being considered as the plant of choice as a ground cover, but is being looked at more for seed production and use in managed landscapes.

Dacus proposed using native plants five years ago, just after joining the Department of Transportation.

But a major problem was the lack of low-cost methods to establish the native plants like there is for planting the ubiquitous Bermuda grass.

Highway areas are planted with Bermuda grass through hydroseeding - shooting the seeds out of a water truck. It would cost four to 10 times more to hand-plant the grass compared with hydroseeding, Dacus said.

While Bermuda grass is a low-cost and effective plant to grow, “;the right thing is to start to use native plants and do something for the ecosystem,”; he said. In turn, the highways will become a seed bank and vector for spreading more native plants around the state, he said.

Dacus expects the DOT will begin reaping the benefits of the $93,750 project in 2010.

The native plants being researched by DeFrank and Baldos will require no permanent irrigation system or mowing. The goal also is not to use herbicides and instead “;reap a lot of environmental benefits,”; Dacus said.

The DOT also began a naturalization maintenance pilot project along rural H-2 freeway areas last year to increase the beauty of the roadside.

“;The highway will be greener-looking and fit better in the landscape by allowing the natural bordering vegetation to grow closer to the road and allowing the road slopes to blend into the surrounding areas,”; Dacus said.

The department is working on expanding the project to other rural roads.

Both the hydroseed and naturalization projects will reduce erosion but are separate, complementary efforts, Dacus said.

Meanwhile, the DOT also has engaged another native plant expert, Rick Barboza, for a research and construction project at the Halawa Interchange.

Barboza, who writes the “;In the Garden”; column for the Star-Bulletin, “;will be developing a native dry grassland forest hydroseed mix composed of species that originally were found in the Halawa Interchange area,”; Dacus said.

While DeFrank's research is aimed at areas where ground covers are preferred, Barboza's project, set to begin this summer, will be for forest areas.


Write to “;Kokua Line”; at Honolulu Star-Bulletin, 7 Waterfront Plaza, Suite 210, 500 Ala Moana Blvd., Honolulu 96813; call 529-4773; fax 529-4750; or e-mail .(JavaScript must be enabled to view this email address).