Pond-side planting suggestions - Zone 8b

Jane McGary via pbs pbs@lists.pacificbulbsociety.net
Tue, 24 Nov 2020 11:17:32 PST
What will do well in the Pacoific Northwest setting described depends on 
the degree of drying experienced in the summer. I have experience with a 
natural pond in the Cascade foothills and with a constructed "bioswale" 
or "rain garden" in my present garden. The latter comprises deep, 
layered soil and gravel strata confined on the downhill side by a soil 
berm, and I had to install it in order to comply with county regulations 
connected with the installation of my large greenhouse. The natural 
pond, in woodland, dropped 1 or 2 feet in summer but still had enough 
water to host ducks, newts, etc. The bioswale has a little standing 
water in winter (it works) and gets some incidental irrigation in 
summer. The first thing to understand is that once you disturb a moist 
habitat, every grass and weed from miles around will sow into it.

I have a lot of Camassia (several species) in the bioswale, but this 
spring deer ate all the flowering stems. I grew it all from seed, and it 
didn't take more than three years to flowering. Now it self-sows 
heavily. On the berm there are a lot of Oncostemma (Scilla) peruviana, 
which I put there after seeing it in similar habitats in nature. Several 
fall crocuses also do well on the berm. I had Erythranthe (Mimulus) 
cardinalis but found it too invasive. E. (M.) guttatus I would think 
requires moving water to flourish, and this is also true of other 
herbaceous (former?) Mimulus. I think Lilium pardalinum also requires 
moving water near it, but not over it; plants I put in a moist but not 
perfectly drained area died out after a few years. The county agency 
that deals with such things gave me a list of "appropriate plants" for 
the bioswale, almost all native species and mostly things I would never 
allow in a maintained garden (e.g., Thimbleberry, Rubus parviflorus). 
The main shrub I have used is a Japanese willow, Salix chaenomeloides, 
which has very large pink catkins and can be pruned for control; it does 
not spread underground. Some plants I'm allowing in the wet part are 
lily of the valley (Convallaria maialis), Caltha selections, Iris ensata 
(wild type), and a non-spreading double Ranunculus. Doing well on the 
parts of the berm that dry out some in summer are Dodecatheon spp. The 
typical choices of vegetation for bioswales are "ornamental grasses," a 
phrase I usually regard as an oxymoron, but if you can limit it to those 
that are not stoloniferous, I suppose they're fine, as long as you don't 
want to grow bulbs within their zone. The Primulas that Jan recommended 
are fine only if their site remains consistently moist through summer; 
they do best in streamside situations in the Northwest.

I didn't plant much around the natural pond because the water level 
fluctuated so much, it was in the woods, and there were plant predators 
such as deer and mountain beaver (Oplodonta). The banks did not host 
many of the rich flora of the surrounding woodland, but red huckleberry 
(Vaccinium sp.) grew well there and is not invasive. In the swale above 
the spring that fed the pond, there was a huge patch of coltsfoot 
(Petasites frigidus), which is not something to turn loose in a garden, 
although in the wild it can be quite ornamental, especially in early 
spring. The same is true of western skunk cabbages (Lysichiton spp.). 
This is a good example of why one should have experience with native 
plants before introducing them into a garden where they don't have acres 
to spread out. I was fortunate to spend my first 25 years of Northwest 
gardening among a diverse rural plant community, so I knew what to avoid 
once I downsized to a half-acre in a suburb.

Some correspondents have recommended plants of moist habitats in eastern 
North America, but these generally do not do well on the Pacific coast, 
probably because of low summer humidity.

Jane McGary, Portland, Oregon, USA


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