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Eugene Weekly : Gardening : 8.25.11

 

Some Like It Soggy

Winter wetness challenges local gardeners

by Rachel Foster

Marionberries are coming on thick and fast in the garden. So are plums, wax beans and, following a very late start, tomatoes. Another reminder that summer is well advanced: A magnificent stand of black-eyed Susans is in bloom next to the alley. I’m talking about Rudbeckia fulgida (Goldsturm strain), that ubiquitous, long-blooming, bright yellow daisy with stiff, orderly ray petals and a velvety black center. 

I have always liked this plant for its clean, dark green foliage and the ability to support itself. I haven’t always found it easy to grow well, though, and I have long suspected it prefers more moisture than I am willing to deliver. It was well established here before we acquired this garden, in a sunny location that seems to confirm that moisture is key. This part of the yard is squelchy all winter and most of the spring, and even in summer requires no irrigation. 

While underlying clay is presumably the cause of our high water table, the top foot or more of soil near the alley is not clay but loam enriched by years of mulching with wood chips. When we first began to dig there (in late winter) we brought up foul smelling gray mud. Within half an hour or so, the smell had dissipated and, amazingly, the color of the soil had turned to dark brown, just from exposure to the air. The same transformation must occur naturally in late spring, as the water level drops. Yet the depth of oxygenated soil is clearly limited — dandelions are easy to remove because the taproots  are only four inches long!

Rudbeckia isn’t the only plant that likes it here. A blue New England aster is almost as rampant, and sundrops (Oenothera fruticosa) appeared to be doing fine until the other two thugs won out with their superior bulk and speed. Given that winter wet presents quite a challenge to a gardener, I’ll take what I can get. At the same time I am deeply interested in learning what else will put up with these conditions. I’ve added a common rush and a couple of clumps of tufted hair grass (Deschampsia caespitosa), both of which I expect to be happy here. But another part of the garden is dedicated to native wetland shrubs and grasses. Down by the alley I’d like to do something different. 

What do the aster, rudbeckia and sundrops have in common? They are all perennials that spread by rhizomes — horizontal modified stems — that creep along the soil surface, rooting as they go. In winter the top growth retreats to dormant buds at soil level. Waterlogged soil doesn’t appear to bother them. Perhaps the shallow roots just rot away, to be replaced by new ones in spring. Most shrubs and trees, and more static perennials with woody crowns or deeper roots systems, won’t tolerate conditions like this. Other rhizomatous perennials would seem to be my best bet. 

Loosestrife (Lysimachia punctata) with two foot spikes of yellow flowers, is going over as black-eyed Susans start. But I’d rather try gooseneck loosestrife (L. clethroides) which has gracefully arching, tapered spikes of small white flowers. This is a quick traveler and I may regret it, but shallow-rooted plants are fairly easy to remove and nothing it could invade here is irreplaceable. Monkshood (aconitum) is a possibility. There are early and late blooming varieties, in many shades of blue. Turtlehead (chelone) would provide another color (mauvish pink), as would pink meadowsweet (Filipendula purpurea). For very late color I have planted crimson flag (Schizostylis coccinea). It’s a long shot, but it over-wintered. I am waiting to see if it will bloom. 

Not far from the black-eyed Susans is a tiny, intermittent spring which breaks the surface and forms a little bog. Too small, alas, for a gunnera, that prehistoric looking giant, but I’m considering an ornamental rhubarb or perhaps a skunk cabbage. I’ve already planted a bright red hybrid cardinal flower (Lobelia cardinalis) and variegated sweetflag (Acorus calamus). The elegant long leaves are thickly bordered with creamy white. I’ll probably plant the much smaller Japanese sweet flag (A. gramineus) along the margin of the dry stream bed we’ve built in an attempt to speed up the drainage of our vegetable garden in the spring. 

The common white calla (Zantedeschia aethiopica) is apparently unique in its genus for tolerating very wet soil. I have this plant elsewhere in the garden, where it looks miserable for lack of water. Maybe I should try it near the bog garden, where the big, glossy leaves would make a welcome contrast.

Rachel Foster of Eugene is a writer and garden consultant. She welcomes suggestions for her bog garden and can be reached at rfoster@efn.org