Wednesday, October 28, 2009
Last Friday morning, as I was working near the pond, I bumped my head on the Persian Vitex for about the umpteenth time. After the obligatory period of cussing and fussing, and wishing I'd planted it at least a few more inches back, I took a look at that area and had a brainstorm. If the bed were just 12-18 inches further out into the path, I'd be unable to walk into the trajectory of the offending branch. And that's when the lightning bolt hit: because this part of the path usually ends up flooding during heavy rains, it would make a great spot for a rain garden! Next thing the Head Gardener knew, I'd dragooned her into moving concrete pavers and river rock around to enlarge the bed.
Having attended a session on rain gardening at the Garden Writers' symposium in September, and taken a few hopefully cogent notes, I thought I'd share what I learned and tell you about how my process differed. I was really pleased that the speakers, Helen Kraus and Anne Spafford, gave some definitions that helped me better understand the difference between wetlands, bogs and rain gardens. A wetland, they told us, has standing water and thus is wet all the time. In a bog, however, the soil stays saturated (so you don't see the water that's there). Dry soil conditions mean low moisture around the roots AND the crowns of the plants. A rain garden, according to the speakers/co-authors of RAIN GARDENING IN THE SOUTH, falls somewhere in between wetlands/bogs and dry conditions. In choosing plants for a rain garden, you're looking for plants that can tolerate not only short periods of flooding but also extended periods of drought. (The inconsistent moisture levels mean that edibles aren't well suited to rain gardens.) You want to site your rain garden not less than 10 feet from your house and choose a spot where you'll get the maximum catchment. You don't want water to stand in the area for over 3 days. Here in my part of Texas, I imagine mosquito dunks or mosquito bits would be necessary if water stands for longer than 24 hours.
The authors' process for making a rain bed starts with digging out the area for your rain garden. If you have clay soil, as I do, 3 inches deep is sufficient. Sandy soil should be dug out 6 inches. You berm up the soil on the low side of the rain garden and amend the bed area with compost. Strictly speaking, a rain garden should be near a downspout or have a swale leading from a downspout to the rain garden to channel the flow of water and slow down the water velocity. Once you've directed the water flow from the downspout, you can plant and mulch. Then wait for rain!
My process was a little different. I'm not a real stickler for the rules, have y'all noticed? This rain garden is not near a downspout and I did nothing to direct the flow of water. The area behind the moss rocks in the picture above is the rain garden. The original path area was crushed granite. Weed problems led me to put a layer of river rock on top of the granite and embed 12 inch square concrete pavers in that rock. To make my rain garden, I pulled up about 6 to 8 concrete pavers and raked out a good portion of the river rocks. I moved the moss rock edging from just under the walking iris you see at the top of the picture and stacked it to make a new front edge.
The Head Gardener, prudent soul that she is, had cautioned me to make sure that the area beside the pond was graded properly. As she pointed out, we didn't want the soil from the rain garden washing into the pond. I assured her that I'd been careful in my arrangement of rocks and in my digging but I did a little judicious watering to test the drainage, as seen below. The Head Gardener allowed me to add the rest of the compost afterwards but said she'd reserve judgment on the quality of the construction until the next rainstorm. (More on that shortly.)
After filling the new bed area with compost, I planted some walking iris, Louisiana iris and a pitcher plant (Sarracenia 'Dana's Delight). I set my one gallon pots of Indian Pinks in the area to see how they handled the light conditions there over the next few days. I also set a small birdbath just under the abusive branch of the Persian Vitex to make sure I couldn't run into it!
After having spent several hours over the course of the weekend getting this accomplished, my next goal was to see what happened in an actual rainstorm and Mother Nature obliged me on Monday with a downpour. While it wasn't of the epic proportions experienced back in April, it was still a very impressive storm. The rain garden performed nicely: it was fairly soggy by the time I was able to get out there and take a look around 1 p.m. Monday.
None of the soil washed into the pond, however. In fact, the pond overflowed into the rain garden which seems serendipitous. The path still flooded but I was expecting it to do so; this was much too small an area to make a significant difference. In case you're wondering (because I would be) "then why do it at all?", I'm big on experimenting in the garden. I wanted to see whether it would work on a small scale and get a feel for the process. It's possible I'll do something of this sort on a larger scale out front in tandem with the new drainage being installed next month. The Executive Producer and I decided we needed to do something to prevent a repeat of the damage done by April's floods. Current plans call for gutters to be connected to a drain that will run under the path on the south side of the house (west of the area pictured), through a bed in the front and then out to the street. I'm hoping we can tweak the plans and install downspout diverters of some kind to channel the rain into the front gardens. The Head Gardener and I both really hate the thought of all that rain going out into the street and down the storm drains.