Snoqualmie Valley Master Gardeners Instruct Today's Lesson in Weeds 101

Thank you to Ann Acton of the Snoqualmie Valley Master Gardeners Association for this very informative guest post on the basics of valley garden weeds.  When it arrived yesterday I was actually in my own backyard battling the plethora of weeds that had sprung up.  I have the sore back and arms to prove it, too.  Read on…

About this time of the year – the 4th of July holiday is history, the sun is finally out in full force – we should all be enjoying our yards, relaxing on patios and decks, admiring our previous months’ hard work. So why am I not lounging on the patio, lemonade in hand? The Three W’s: Wildlife, Weeds and Water. While the deer and rabbits are testing my patience this year, the weeds are at the forefront of my personal garden struggles, so we’ll start there.

A major benefit of living in the Pacific Northwest is that the soil is generally good and the climate is moderate – excellent conditions for growing a wide variety of plants, including weeds. And what is a weed? Ralph Waldo Emerson proffered that a weed is a “plant whose virtues have not yet been discovered.” It’s one that has no value in the location it’s growing, and yet in some situations it may be the perfect plant, or at least tolerated. Clover is a good example: it’s not welcome in some lawns and yet is desirable as a groundcover that not only prevents erosion on slopes, but improves the soil as well.

My own garden where it seems (at times )weeds grow faster than any plant in it!

Generally though, we just want the weeds to die. Trying to control weeds is probably one of the most time-consuming and frustrating tasks in the garden – they’ve adapted to all environments and are extremely prolific – some can produce over 500,000 seeds per plant! After years and years of exasperating struggles, I’ve recently come to accept that total elimination is not possible and if I can just minimize their impact, I’ll be content.

In order to get some control over weeds, it’s advantageous to know that they are classified as annual, biennial, and perennial according to their life cycles. Once we know what we’re dealing with, an integrated approach to weed control can be formulated. To be sure, every yard contains every classification of weeds so no single tactic will be successful; combining different strategies is the way to go. We can physically and mechanically deal with weeds by pulling them out, mowing them down or torching them. We can smother them with mulch and include competitive plants in the landscape. And we can use chemical control when all else fails.

Annual weeds germinate, grow, flower and produce seed within one year. Those seeds can germinate right away or some time later when the soil is disturbed and they are exposed to light. Little bittercress (shotweed) is a common annual weed whose innocuous early rosettes produce dainty little flowers and explosive seed heads. The key to controlling annual weeds and interrupting their seed production cycle is to “pull early and pull often,” according to a master gardener colleague. Application of mulch will also deter annual weeds by creating a physical barrier between the seed and the soil, and also smothering potential germination underneath.

Biennials germinate and produce leaves the first year and then flower and set seed the next year. Foxglove is biennial: it grows flat leaves close to the ground, overwinters and then in spring it grows rapidly from thick roots. Due to their two-year cycle, these weeds are by far the easiest to control by simply removing with a hoe or hand pulling. Again, the key is to get to them early in the spring; if they’re allowed to flower, seed setting is close behind and the cycle begins again.

Perennial weeds can be the most challenging to eliminate. They have a root system that persists from year to year even if the visible leaves are removed; horsetail, dandelions, blackberry and buttercup are some notable perennials. Repeatedly removing the tops (mowing them down) and persistently digging out the roots will pay off over time. When all else fails, application of the least toxic selective (specific for the weed you’re after) herbicide on the leaves and cut stems will eventually kill the roots. In all cases, read the label and use the recommended amount – more is not better – and never use in food gardens.

There are of course a variety of other weed control tactics and preventions. Cover an area with black plastic or cardboard and mulch over it to effectively control weed growth where you don’t want to plant anything for a couple of years. A handheld flame torch is effective for gravel paths and driveway cracks.

Permanent weed control lies in treating the cause of the problem as well as dealing with the symptoms. Composing a yard and garden with a complement of plants that thrive according the area’s conditions (soil, light, water), creates a healthy competition for the plants (weeds) that we find undesirable.

The vacant lot close by is finally being mowed today after the fourth flush of yellow dandelion flowers and subsequent puffball seed heads. I’m sure there will be dandelions to pull in my yard in the future, but for the moment, I’m okay with the few weed seedlings I see. Tomorrow, they’re toast!

Bring your unidentified weed to the Master Gardener booth at the North Bend Farmers Market now through September. Information on the Three W’s and other gardening tips can also be found at the Snoqualmie Valley Master Gardeners’ website at

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