Kill Before You Till

Is this a familiar sight? Bermuda grass is the bane of this gardener. Typically, directions for development of raingardens in native soil are to check permeability, clear the site, till in compost, and plant. But digging up sod in Illinois is different than removing the grass in Oklahoma.

Our primary grass seems to be Bermuda and it is invasive! Bermuda spreads not only by seeds but also by runners above and below ground. It can overtake over a foot of garden in a growing season. So, simply taking off the top layer of sod won't do. You have to kill it.

But how? I checked with the County Extension Office office for some direction. And their advice confirmed my anecdotal experience: Bermuda is tough stuff. You can try thermal sterilization of soil - putting down black plastic and allowing the sun's heat to kill everthing off. This kills the surface plants but doesn't address the deeper roots, which can be six inches or more below the surface. This also kills plants by depriving them of sunlight, but Bermuda can stay dormant under the soil for an extended period of time. I've also tried herbicides, which seem to work for a while, but Bermuda always seems to come back.

Bermuda, it seems, must be killed and killed again. They say up to 6 or 7 sprayings over time are necessary to really eradicate Bermuda from a proposed plot. And that takes planning ahead, about a growing season ahead, of when you want to plant.

And because it continues to spread from the outside, placing a good quality edge to 6 inches beneath the soil (not extending above the ground) will help minimize root intrusion. Surface runners take a hands-on approach. After all that, you should have a garden that is much easier to maintain. But it takes some time and planning (and a bit of grass-killer).

Traveling LID: Florida

As you may have guessed, I have to make note of LID applications wherever we travel. We took a family vacation to Sanibel and encountered these raingardens in a small county park northeast of Ft. Myers. We went to watch manatees, which we didn't see, but we found multiple raingardens!

Much of Florida is condusive to bioretention, a fancy word for raingardens, because of its sandy soils and high infiltration rates. As you can see in these photos, the surrounding landscape has been graded to form a depression. This is where rainwater collects. Plants within the depression have been selected that can withstand periods of standing water, or inundation. And the water is allowed to infiltrate, or seep into, the soil.

Some of the things I liked about this park were the number and variety of raingardens present - in the parking lot, at the entrance, and scattered throughout. They also provided educational signs, which I don't have photos of. I also liked that they made use of a range of vegetation, from trees that look like they've been there forever (and they may well have) to bushes and groundcover. Its not obviously a stormwater treatment system but fits attractively into the overall landscape. Kudos!

Who Designs Raingardens?

I was recently asked to come out and look over a new raingarden that had been designed by a reputable local landscape architecture firm. But I had been asked to take a look because it really didn't seem to the owner (a public entity) to fit the definition of a raingarden. Sure enough, the garden fit right into the profile of the slope, and did not provide a means of detention or opportunity for infiltration. I checked the design drawings which provided a planting plan with a note to set the garden six inches below the surrounding surface - not a bad start but not really a raingarden design. But it made me think again about a question I had received previously - who designs raingardens and why?

I checked with the Board of Professional Engineers for Oklahoma and the Board for Landscape Architects. And there is some confusion. Apparently there is joint commission that discusses and decides on such issues and I recommended that this could be a good question to consider. The feedback I received was that landscape architects should develop and stamp landscaping plans. But because LID features are designed, or should be designed, for stormwater collection, conveyance or treatment, the sizing and hydrology (how much water and where it goes) should be stamped by an engineer. Ah, interdisciplinary design. We get to all work together. Now, if we just would.