Japanese Knotweed

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Japanese knotweed, an ubiquitous, exotic invasive plant in the Pittsburgh region, can make gardening difficult if not impossible. The weed spreads rapidly by seed or by root. Digging out the plant just encourages new ones to sprout, from rhizomes left in the soil. These rhizomes can be found as deep as 10ft! Even chemicals are usually a temporary fix, due to the resilience of the plant.

knotweed, full

Knotweed hails from Asia and according to the USDA, it was introduced in the late 1800s as an ornamental. It’s a wildly successful plant, tolerating a wide range of soil types and pH, and it easily colonizes land that is not constantly tended. It easily outcompetes native plants. In Pittsburgh, you’ll find it on roadsides, by the river, on steep banks, beside houses and sidewalks, on vacant lots, and in yards – basically everywhere!

Japanese knotweed looks somewhat similar to bamboo, with hollow stems. The leaves are oval and the plants reach up to 10 ft tall, in optimal conditions. It develops flowers in the summer and on a positive note, it’s regarded as an important source of nectar for bees.

knotweed, closeup

Since knotweed spreads and overtakes other plants, we recommend avoiding areas infested with knotweed, when planning your garden space. However, if a knotweed-filled area is your only option, we’ve got some hope for you. A lucky mistake at the Urban Gardener indicates that pumpkins might give knotweed a run for its money. If the preliminary results hold true, knotweed control may simply be a pumpkin patch away!