It’s a hilly country we’re clinging to. Northwest Philadelphia is the beginning of the Piedmont region of Pennsylvania, which is usually characterized by rolling hills, or in our case, steep rocky slopes.
Philadelphians have been altering the landscape for so long, it can be hard to remember that there is pretty much no naturally flat ground in our area. Despite the elaborate retaining walls and embankment systems that have been constructed in our city throughout the last 300 years, inevitably there are some steeply sloping properties. I now own one of these, and have begun a mini-adventure in gardening on a slope. The learning curve, like the yard, is steep.
A year ago this 60 degree slope was covered in English ivy, Japanese honeysuckle, a couple of wild cherries, and many Norway maples, which had opportunistically taken over during the long time that the property was vacant. Most of the trees have been removed now, but the stumps and some of the vines were kept to help anchor the poor soil that hadn’t already washed into the street.
What’s new are about ten small trees, which will become much bigger if I can prevent them from falling out of the ground. It’s a challenge to get a tree settled in on a slope, because once it’s set in a hole one side is buried too deep, while on the other side the roots are still exposed. I solved this issue temporarily by pounding a couple of three foot long pieces of rebar into the ground in front of each planting location and wedging a plank on its edge behind it, like a stair riser. By backfilling the plank it created a fairly flat area in which to plant.
The planks are still solid, although eventually they’ll begin to rot. Hopefully by then the tree roots will have grown into the soil enough so the tree won’t topple over, otherwise I’ll have to put in some new boards.
When choosing what I wanted to plant, I thought about trees that I often see on sloped locations. Eastern Red Cedar was the easy one. This is the evergreen that you see on the sides of the highways up and down the East Coast. It’s very tough, and the birds really like the tiny cones. It’s not considered a very genteel tree, and so it can be difficult to find but worth seeking out.
I also put in some old fashioned crab apples, on the theory that since a lot of the orchards I’ve visited are on hills, they might handle a slope better than other trees.
So far, so good. Everything has stayed perfectly upright for three months (except the perennials, but I’ll go into that on my next post.) But it looks like the slope’s first real test of its mettle may come this weekend. Hurricane Irene, are you going to spare my slope, or will you topple my trees?