There’s nothing like a few minutes of heavy downpour to check that the garden’s ecological systems are doing what they’re supposed to.
Today brought pounding rain and hail to the garden. There’s standing water over the gravel in one area, the rain garden is filling up, and the pervious paving is definitely working hard.
Once the soil is saturated, pervious paving doesn’t do much except slow water flowing through the gravel – so in effect the gravel becomes a storage medium, with the spaces between the stones completely filled with water. When the rain lets up, the water levels should drop as the water penetrates into the soil.
In the rain garden, plants will draw water out of the soil, and the rest will either evaporate or slowly move underground. It hasn’t remained wet enough to injure any of the plants, since they’re adapted to wet spring conditions.
The benefit of this kind of garden is that there’s no huge surge of runoff from the garden. Most of the water is initially captured by the paths and rain garden which then fill as the storm progresses. As this storm continued, water began to flow over the surface of the soil, but as soon as the storm let up, the water began to sink into the soil. This treatment mimics nature, where water is trapped by vegetation, duff and permeable soils instead of instantly running into rivers and streams. In urban environments, the opposite is true, where water moves into gutters and storm drains from hard, impervious concrete, asphalt and roofs.