Bulbs in a bioswale

Jane McGary janemcgary@earthlink.net
Sun, 27 Mar 2016 13:23:44 PDT
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

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