top of page

Good Plant / Bad Plant

by Tim Kennelty

Column #1 – Oaks and Japanese Knotweed

This is the inaugural edition of Good Plant/Bad Plant, a new recurring feature of the TGazette. Each edition will focus on two plants — one that supports pollinators, birds or other animals and is valuable in the environment — and one plant or plant group that is invasive or a noxious weed.

So, with our inaugural edition I would be remiss in not talking about what Doug Tallamy (the native plant guru) calls “the most powerful plant” — the mighty oak. When I say, oak, I’m talking about the genus “Quercus” and I’m really referring to oaks that are native to our area, like white oaks, red oaks, swamp white oaks, scarlet oaks and a few others.

Oaks can grow to 80 feet tall and can live from 200 to 400 years. Red oaks, scarlet oaks and pin oaks have fibrous root systems and are fairly easy to transplant, while white oaks have tap roots and are best planted when saplings. Oaks are generally relatively easy to grow, and thrive in well-drained, acidic soil in full sun. They are beautiful, majestic trees, often with attractive fall foliage in shades of red, gold and orange.

So why are oaks so important to the ecosystem? First and foremost, they are what Tallamy calls keystone species — those that define an entire ecosystem, particularly in supporting insects, that are subsequently consumed by birds. Oaks support more than 500 caterpillar species which turn into butterflies and moths but are also critical food for most fledging young birds. They’re also great at sequestering carbon and pumping that carbon into the soil. Acorns produced by oaks are eaten by squirrels, deer turkeys and other birds. I could go on and on about oaks but suffice to say if you can only plant one tree in your yard and you want to support wildlife, plant an oak.

As the Oak is the king or queen of beneficial plants, I’m crowning the king of invasives or bad plants – Japanese Knotweed or Fallopia japonica. Knotweed is a member of the buckwheat family. Like many invasive plant species, it was introduced as an exotic ornamental from Eastern Asia in the 1800s. By the 1930s it was already being recognized as a problematic pest.

Knotweed can grow from 3-15 feet and has bamboo-like stems. It’s even been referred to commonly as Japanese bamboo. It thrives in disturbed areas like drainage ditches, wetlands, streams and woodland edges and along roadsides. Knotweed spreads rapidly through underground rhizomes. A single piece of rhizome that breaks off can easily create a new plant and add to the spread.

Knotweed can have a devastating environmental impact as it forms dense thickets that crowd out and shade native vegetation. These monocultures reduce species diversity, adversely impacting ecosystems and wildlife. A dense stand of knotweed can also contribute to soil erosion.

As for identification — during spring, reddish, purple shoots appear from a network of spreading rhizomes, and develop into asparagus-like spears that grow very rapidly. By early summer, the stems are hollow with purple speckles and the leaves alternate along each stem with a zigzag pattern. In late summer distinctive creamy colored spike-like flowers emerge.

Knotweed control (and control not elimination is going to be our practical objective with invasive plants) can be a multi-year project focusing on reducing the rhizome network. Management includes repeated cutting and most likely will require herbicide application. For much more information on identification and control of knotweed I’m including some links to trusted sources. It’s always better to know your foe.


Taghkanic resident, Tim Kennelty is a Master Gardener and Master Naturalist volunteer through Cornell Cooperative Extension, and is the co-host of Cornell’s weekly Master Gardener podcast, Nature Calls: Conversations from the Hudson Valley. For more about gardening and nature, listen to our Master Gardener podcast, Nature Calls, Conversations from the Hudson Valley, available on all major podcast platforms and at

Additional Resources on Oaks:

Additional Resources on Japanese Knotweed

218 views1 comment

Recent Posts

See All

1 Comment

Mar 29, 2023

This is a great column idea, thanks! For several years I've been battling something similar to the knotweed -- I believe it's called wild Asian rose or something to that effect. Really nasty thorns that make removal in season difficult. It wraps itself around trees, a la Little Shop of Horrors, and effectively strangles them. Removal calls for thick gloves and pants (chainsaw chaps preferred) and a willingness to wrestle with live vegetation,, sometimes to the ground.

bottom of page