Behind the Scenes at the Weed ID Garden

WSU Whatcom County Master Gardener Program

By Janis Walworth, WSU Whatcom MG 2009

Managing a weed garden is unlike tending any other kind of garden. You’d think growing weeds would be easy — we all do it effortlessly in our yards. But getting weeds to grow where you want them can be difficult.

The first problem is obtaining the weeds. You can’t order seeds for most weeds as you do for vegetables. You can’t pick them up at a nursery as you do ornamentals. Many of our weeds come from Master Gardeners’ yards, but we don’t have the full range of weeds we want to display. The others have to be hunted down.

Once a weed is located, it has to be identified. Then we research information about each weed and create signage showing its botanical name and family, common names, origin, life cycle, and flower color, as well as management tips and interesting facts.

Some closely related weeds can’t be identified with certainty until they bloom, but we want to be able to label them when they’re young. Therefore, we start some weeds from seed so we can be sure of what’s growing.

With weeds coming up from seed all over the place, you’d imagine they’d be easy to grow, but that’s often not the case. Most cultivated plants have been bred to germinate readily when the seeds are put in soil and watered. Not so the weeds.

The seeds of each weed species have requirements that have to be met before they will germinate. Some need a period of cold and wet, others need temperatures that fluctuate in a certain range. Some need to be scratched on the surface. Some, like blackberry seeds, won’t germinate until they’ve passed through an animal’s digestive tract.

Each weed seed is a puzzle to unlock. And instructions are hard to find. No one posts tips online on how to grow weeds. (How to grow weed is a different story, one that makes internet searches on weedy topics challenging.)

Perennial weeds that come up each spring from roots can generally be dug up and potted without much difficulty, although there are some that don’t transplant easily. Horsetail, for example, has thin, very deep roots, making it surprisingly hard to transplant successfully.

Once we’ve captured the weeds, the next step is keeping them alive. We have to position them so they get the right balance of sun and shade. We water them once or twice a week, depending on the weather.

We grow all our weeds in containers, but that cramps the style of some weeds. They can’t send their roots far down to extract nutrients and moisture, so we have to irrigate and occasionally even fertilize them.

We try to keep our weeds looking the way people see them out in the world. We prune them a little, not to make them look nice but to keep them from encroaching on their neighbors or obscuring the signs.

Like other potted plants, weeds growing in containers have to be periodically removed and thinned. The roots often need pruning. Our knotweed plant expanded its roots so much they burst the sides of a 5-gallon bucket.

Once we have our weeds growing well, the next challenge is to keep them from spreading. Growing weeds in containers helps to prevent roots and rhizomes from extending underground. Our containers have small holes in the bottom for drainage; we check them periodically to make sure no roots are finding their way out.

We like to leave flowers and seeds on the plants so visitors can observe them, but every week we thin them so they don’t produce too many seeds. Weeds with exploding seed pods that shoot seeds several feet and those with wind-dispersed seeds call for special vigilance. We tend them twice a week when seeds are ripening.

Hovander Park is in a flood plain. The area where the weed garden is can have 2-3 feet of water rushing over it, leading to concerns about weed seeds and regenerative plant parts being carried away and starting new infestations, perhaps miles away.

Every October, the weeds are moved in their containers to higher ground for the winter. Perennial weeds survive the winter in their containers, needing little care. Annuals and biennials have to be gathered again in the spring.

We are constantly striving to improve our management of the weed garden. We have to be innovative because there aren’t many examples to follow. Through online research, I’ve been able to locate fewer than a dozen weed identification gardens in all of North America. We’re very fortunate to have one here.

Janis