Giant hogweed, also a Class A noxious weed, is very dangerous to people due to its toxic sap that causes burns. In the spring, look for large, jagged-looking leaves growing in clumps and stems with stiff white hairs and purple bumps. In the summer, mature plants are topped by 10-15 foot tall stems topped by giant umbrella-shaped flower clusters. This exotic species is very similar to a native plant called cow parsnip, which is also emerging now. For help distinguishing them, send photos to our noxious weed specialists and we can help sort it out. Both plants have dangerous sap so make sure to wear gloves when handling either species.

Poison-hemlock is a Class B noxious weed (control required on public lands and roadways). We just covered this plant in this blog so I’ll keep it short and simply repeat that it is very poisonous and should be controlled where ever possible to prevent people from getting hurt. There are many look alikes when the plants are small, but poison-hemlock stems are not hairy and do have purple spots, so look for both characters to narrow it down.

Lesser celandine is one of those plants that has fooled many people into planting it, or underestimating its impact. It’s a low-growing relative of the buttercup that forms dense patches. It emerges super early in the spring, is already in full flower in March and will be in seed by May, after which it dies back and goes dormant until the following year. It spreads by seeds, bulbils that form on the stems, and tubers that form on the roots. Once it’s in the soil, it is nearly impossible to get rid of without considerable effort and persistence. Unfortunately, it can be spread in topsoil and mulch so make sure your landscape materials are coming from a safe, weed-free provider.

Italian arum is another plant that spreads in topsoil and mulch, possibly helped along by squirrels! It has attractive shiny leaves with white marbling that emerge in late winter to early spring and produces interesting looking stalks with red fruits in the summer. Sadly, it also has irritating and toxic compounds that can cause problems for people handling it and for animals eating it. Controlling it is very hard because of the numerous tubers it forms in the soil. The numerous tubers often fall off the roots when you pull the plants. It often shows up where yard waste is dumped, spreading out from there to take over in natural areas and parks.

Scotch broom is a very familiar invasive weed on the west coast and is so widespread people new to the area may think it’s a native plant (in spite of the name!). Scotch broom has become entrenched in this part of the world but it was originally brought here from Europe both as an ornamental species and for erosion control on slopes and roadsides. Scotch broom starts flowering about now but isn’t usually in full bloom until later in the spring. If you have allergies, Scotch broom in flower can trigger terrible headaches just from the odor alone. And don’t get me started on how long-lived the seeds are, how invasive it is, or how much of a fire hazard it is!

Gorse, a relative of Scotch broom but much meaner, is a Class B noxious weed with control required in King County because it is relatively limited here. Look for golden-yellow flowers starting in late February and stems covered with sharp, stout thorns. The bushes are large and dense, making control a big challenge. Gorse also contains a very flammable oil so it can create a big fire risk as well as being invasive.

European coltsfoot is a relatively new Class B noxious weed we are looking for and controlling in King County. It has the strange pattern of flowering in February on leafless stalks and then leaves emerge in spring after it starts to go to seed. By summer all you see are the leaves. It is similar to our native coltsfoot in how it grows, but European coltsfoot has yellow flowers and leaves that are not deeply lobed. Native coltsfoot has white flowers and deeply lobed leaves. European coltsfoot is showing up in two main areas in King County: natural lands near water where there is a lot of natural disturbance and gravel piles. The plant thrives on disturbance which allows it to fragment and spread by rhizomes. Although not that difficult to control individual plants, large infestations are difficult to eradicate because of this spread by rhizomes.

Spotted knapweed is just starting to grow this month. It tends to overwinter as a low-growing rosette and then produce flowering stems in the spring. Right now you will mostly see the rosettes which can be hard to spot. However, if a plant has grayish leaves around here, it’s probably not native, so take a closer look! Spotted knapweed leaves are so deeply lobed there’s really not much leaf surface left. Once it flowers, the stems are taller and topped by little pink-purple flower heads that resemble thistles but without the thorns. Spotted knapweed is a Class B noxious weed that is required for control in King County so we would love to know where you see it.