The first challenge with the rain garden is that the site is already planted up. Clearly, this is the opposite of the ideal situation, but to paraphrase a certain former, uniquely-spoken US leader, we go to war with the site we have, not the site we might want or wish to have at a later time.
I set up a string line (barely visible in the upper right corner of the photo above) to mark the original soil grade. Then, using a garden hose, I laid out the portion of the garden that will be dug to the greatest depth, dug in around the shape’s perimeter, and began moving what few plants were there (initially, years ago, I shaped this garden site as a crescent, but it began, as with all my projects, to creep well beyond its original scope). I removed three gallons’ worth of Iris ‘Eco Easter,’ which has spread magnificently since I received it from a friend a few years ago, and about the same quantity of Petasites japonicus, another pass-along plant that I received last fall but have yet to see in action (I have been forewarned). I dug up and repotted some Rohdea japonica, which is a wonderful foliage plant for dry shade; a Polemonium whose name I forget, and a Pulmonaria ‘Trevi Fountain.”
The weather has been damp, so the clay wasn’t impenetrable.
Here is what 12 inches deep looks like in the area I’ve chosen to excavate. That’s a tree root, perhaps an inch to an inch and a quarter in diameter, you see at 9 inches deep. I expect to encounter many of these. In general, when digging around trees, it’s advisable to avoid severing anything much larger than the diameter of a pencil. We’ll see about that.
I didn’t set out to excavate the whole central area this day, but the weather was nice and I got a bit carried away with myself. I loosened the soil with a small tiller, but I removed it all by hand.
A good first start; the entire area is dug down 6 inches deep. Lots of pencil-sized and smaller roots.
Why have I set myself so much digging, when it’s beyond what is called for in the book? Essentially, I’m not convinced that in my site six inches deep (three, when finished) is adequate. The soil in this part of the garden has received generous and dedicated mulches of leaves and compost over the past, say, seven years, and digging down six inches really isn’t much of a problem. The top layer of soil is plenty friable. But water still puddles here, suggesting to me that at best it penetrates those top six inches and then sits on top of the clay base, and when the loose soil is saturated, as it will get in a typical rain, the rest of the rainfall runs off and is lost. In other words, I suppose, I already have somewhat of a rain garden, but it’s too shallow and the land isn’t adequately shaped to take best advantage of its opportunities.
If When you spot holes in my logic, please do point them out. This is, above all, an experiment.