One of the requirements the county imposed for giving me planning
permission for my greenhouse was the installation of a bioswale ("rain
garden") to capture the runoff that wasn't held by the rainwater storage
tank. Of course I had to put some bulbs in it, even though this habitat
is not one most people think of as suitable for bulbs. However, the
bioswale was created by deep excavation and layers of drainage material,
so it never has standing water in it, and in this climate it becomes
rather dry in summer.
I ignored the list of recommended species (mostly natives, and mostly
things I wouldn't want within 100 meters of my garden). Bulbs I put
there include Camassia spp., Fritillaria camtschatcensis, Fritillaria
meleagris, and Oncostemma (Scilla) peruviana. Also of interest to our
group are Convallaria majalis (lily of the valley), Siberian irises, and
Dicentra formosa. Some of these would be too invasive in a well-managed
border, but in the bioswale they can fight it out with the violets,
annual grasses, clover, and other low-growing weeds that I can't control
there. I do irrigate the area once a week in summer to preserve some
Caltha, Trollius, and Rodgersia which I enjoy. Periodically I try to
eliminate plants I don't enjoy, such as the giant Inula that goes around
seed exchanges under the name "Cremanthodium arnicoides," quite a
different plant.
The downhill edge of the bioswale is retained by a low berm, which
provides a good habitat for small Colchicum spp., Crocus spp., the
Dodecatheons, and other small plants. The uphill edge was supposed to be
home to bergenias and Leucothoe, but it dries out too much for the
latter. Therefore, yesterday I went out to Wild Ginger Farm, a great
nursery in our area, and bought some of Emma Elliott's offerings of
Pacific Coast iris hybrids. Emma, a PBS member, has acquired and also
hybridized many beautiful cultivars of these plants, which do well in
our climate. Many are evergreen, and they quickly form large, dense,
weedproof clumps.
Almost every micro-habitat in a garden can appeal to some bulbs, corms,
or tubers, especially if you tolerate some bare ground during their
dormant periods.
Jane McGary
Portland, Oregon, USA