Solar power will bring flowers -- and kill weeds

NATURAL PERSPECTIVES

The Friends of Shipley Nature Center plan to transform a one-acre

field filled with deadly poison hemlock into a meadow blooming with

beautiful wildflowers. By next spring, a portion of Shipley Nature

Center will be covered with nearly 30 different kinds of California

native wildflowers and bunch grasses, and a low spot will become a

type of freshwater wetland known as a vernal pool.

Several hurdles stood in the way of this grand plan. Finding

funding was the first concern. Fortunately, the Southern California

Wetlands Recovery Project awarded the Friends of the Shipley Nature

Center a $15,000 grant to remove nonnative weeds and plant native

vegetation on two acres at the south end of Blackbird Pond. The

project also includes funds for construction of the vernal pool.

A major challenge was eliminating the poison hemlock. Last winter,

the meadow was filled with the fern-like foliage of poison hemlock.

Lacy white flowers waved with every passing breeze. It looked pretty

to the untrained eye, but poison hemlock is highly invasive, and

every part of the plant is deadly.

Volunteers and workers from the Orange County Conservation Corps

cut back the hemlock with machetes in the early spring. This

technique wasn’t very effective. The hemlock grew back so thick that

it looked like it had never been cut. By early June, the hemlock was

7 feet tall. It had hidden most of the little oak and sycamore trees

planted by children last fall. Volunteers couldn’t find the trees to

water them.

Then the hemlock began to set seed. Hemlock is an annual. If the

stalks could be cut and removed before the seeds dropped, the

wildflower project would have a much higher chance of success because

there would be fewer weed seeds in the meadow. The stalks had become

too thick, however, to hack with machetes.

Poison hemlock covered an estimated six acres throughout the

nature center and was setting seed faster than the Orange County

Conservation Corps workers could cut it. The solution was a

professional-grade, metal-bladed, rotary brush cutter called a weed

whacker. This tool is the big brother of a string trimmer. A discount

from Anchor Tool brought the price down to a range the Friends could

almost, but not quite, afford. The Huntington Beach Tree Society

saved the day by putting up half the purchase price. They will use

the cutter to clear brush in the Urban Forest in another area of

Central Park.

The Friends’ priority was to clear the one-acre meadow. The rest

of the nature center would have to wait. Day after day, the Corps cut

the hemlock, raked it up and loaded it into dumpsters generously

provided by Rainbow Disposal.

When the Corps knocked off at the end of the day, Vic would strap

on the whacker and cut. I used a McLeod combination hoe/rake to

clear. After weeks of work, the meadow was cleared, not only of

hemlock, but of castor bean and giant reed, two other noxious plants.

We removed about six tons of hemlock before the seeds dropped.

The next task was to use the power of the sun to kill weed seeds

in the meadow. Hemlock seeds can live in the soil for three years, so

seeds from previous years’ crops were undoubtedly still there. On the

advice of landscape architect Guy Stivers, the volunteers decided to

use the sun’s energy to kill weed seeds before sowing the meadow with

expensive wildflower seeds. The process sounds simple, but it is a

tremendous amount of work.

The Corps crew supervisor, Benito Ramirez, and the crew leader,

Edwin Coreas, had used solar sterilization of the soil at previous

job sites. They spread roll after roll of plastic sheeting over the

cleared meadow. They filled sandbags provided by Public Works with

dirt to hold down the edges of the plastic. They carefully cut the

plastic away from the newly planted trees to protect their roots.

When the sun beats down on that plastic, the soil under it gets hot

enough to kill. After a month, between 80% and 100% of the weed seeds

under the plastic should be dead.

We were curious just how hot that soil was getting, so we stuck a

thermometer underneath the plastic sheeting. Early in the morning,

shortly after the shadows had moved off the plastic, the soil surface

temperature was 90 degrees. The air temperature was a comfortable 68.

By 9 am, the temperature under the plastic had risen to 115 degrees,

and by afternoon, the soil was cooking at 160 degrees. A few weeks of

that should be enough to kill almost anything.

In late August, the crew will pull up the plastic and reuse it in

another part of the nature center to kill hemlock there. Any

remaining hemlock stubble will be removed from the meadow, and the

ground will be contoured. The area that is to become the vernal pool

will get a layer of clay added to it to hold rainwater. Such a lined

vernal pool will hold water for about three to four months. As the

water in the vernal pool evaporates, a ring of flowers blooms at the

ever-shrinking edge of the pool.

The Friends of the Shipley Nature Center seem to have cleared all

the hurdles on this project. It’s going to be a beautiful and

weed-free show in the meadow this spring, brought to you by the labor

of many people. And by the power of the sun.

* VIC LEIPZIG and LOU MURRAY are Huntington Beach residents and

environmentalists. They can be reached at [email protected].