The taming of a drain field

I'm picturing this: A woman in a summery light-blue frock, moving gracefully through a poppy-filled meadow. Tall grasses wave around her skirts.

The reality is a bit grittier than this Monet moment. I'm actually out on the septic drain field pulling Canada thistles and longing for an alternate Impressionist reality.

The landscape challenge? My drain field dominates the view from my living-room windows.

Gardeners don't stop dreaming. My current dream is drain-field transformation, starting with extracting the nasty weeds and gradually adding appropriate plantings. Even if you don't have a drain field but do think occasionally of meadows, some of my experience with perennial weeds may help.

Clearing established Northwest weeds takes about three years of constant work, followed by a lifetime of attention using several different techniques.

Tall Himalayan blackberries and big Scot's broom plants buried my drain field. No good. The drain field requires shallow-rooted plants with better manners. Drain fields need oxygen in the soil and no soil compaction. Proper plantings can help.

With lots of help, the bad blackberries and Scot's broom were grubbed and removed from the scene last summer. That left me with an unplanted drain field full of perennial weed seeds, plus roots of nasty Canada thistles (a class C Noxious weed), and winter coming on.

A layer of cardboard went down, followed by 4 inches of compost. You might imagine that spring would find this area in a plantable condition. Emphatically not.

Now I'm dealing with returnees — smaller blackberries, Scot's broom springing from seeds, and worst of all, flotillas of Canada thistles.

If you wish to become the perfect weed, choose Canada thistle, also known as Cirsium arvense. The roots penetrate 21 feet or more into the ground, the plant resprouts from pieces of root 1 inch in length, and each mature plant sheds up to 5,000 seeds that can sprout decades after landing in soil. Plus, they inflict pain when touched.

I'm experimenting with various ways of clearing the thistles. The cardboard, which is now disintegrating, slowed them a bit. Underground shoots twirled themselves into slinky forms where they hit the cardboard on the way up to light, but emerged anyway. They're quick. A root segment can regenerate into a plant within five days of being pulled. Nonetheless, I'm continuing to pull, hoping to weaken the roots somewhat.

I don't want any Canada thistle to mature and go to seed this season. ( I already have at least 20 years worth of existing seeds.) Canada thistle doesn't manage shade well, so I've covered two thriving patches with tarps. I'll leave those until fall, hoping that one article I read was correct in stating: "If light's reduced to less than 20 percent, the Canada thistle dies." I just bet.

Canada thistles can be hit with herbicides before bloom or in fall, when the plants are still growing strongly but are sending nutrients down into the roots for winter. In September, I'll treat the hardy survivors with glyphosate (Roundup), painting it on with a brush.

So, yes, I'm spending a lot of time on the drain field. I'm encouraging some local perennials: velvet grass, coastal mugwort, clover and yarrow. I'll sow Ecoturf (a meadow-like lawn mix) and other grasses in fall, toss a few packets of red field poppy seeds out, and hope that by spring the Monet effect thickens up a bit.

I aim for a natural-looking spot with long waving grasses during summer and tawny grass in fall, to be managed with spring weed-whacking before growth starts.

Maybe I should just transplant the Canada thistles. If you want to get rid of a weed, pamper it. The vigorous coastal mugwort plants I moved into new drain field spots died immediately.

Mary Robson is area horticulture agent for Washington State University/King County Cooperative Extension. She shares gardening tips every Wednesday. Her e-mail is gardeningtips@seattletimes.com