Can I prune back leggy stems?

Yes, you can prune back long, weak stems to encourage the plant to branch out and grow more compactly. Use clean, sharp shears to make cuts just above a leaf node.

Will my plant recover its shape?

Once a stem has stretched out, it will not shrink back to a compact size. However, new growth will be much sturdier if you move the plant to a brighter location.

Why is my giant knotweed growing so leggy? Causes and fixes

Check these first

Observe the amount of direct sunlight reaching the plant throughout the day.
Check the distance between the leaf nodes on the main stems.
Review your recent fertilizing schedule for high nitrogen products.

Likely causes

Insufficient Light
Most likely
How to tell: The stems are thin and stretched out with large gaps between the leaves. The plant may also lean heavily toward the nearest light source.
What to do: Move your plant to a spot that receives full sun or at least 6 hours of bright, indirect light daily. If you are growing it indoors, place it directly in a south or west facing window.
Excessive Nitrogen Fertilizer
Possible
How to tell: The plant produces very long, weak stems that cannot support their own weight. The foliage may look lush and green but the structure is flimsy.
What to do: Stop using high nitrogen fertilizers immediately. Switch to a balanced, slow release fertilizer applied only once in early spring to encourage sturdier growth.

Leggy growth in other plants

Find out what's wrong with your giant knotweed

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

When to worry

You should worry if the stems become so weak they snap under their own weight. It is normal for the plant to grow tall quickly during the peak of summer.

Stopping it coming back

Provide plenty of direct sunlight and avoid overfeeding to keep the stems thick and strong.

Giant knotweed: leggy growth? Check yours with a photo

Every plant is a little different. Take a photo of your giant knotweed and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.

Get the app · Or check it from a photo now, free

Questions people ask

Can I prune back leggy stems?: Yes, you can prune back long, weak stems to encourage the plant to branch out and grow more compactly. Use clean, sharp shears to make cuts just above a leaf node.
Will my plant recover its shape?: Once a stem has stretched out, it will not shrink back to a compact size. However, new growth will be much sturdier if you move the plant to a brighter location.

Why is my giant knotweed growing so leggy?