Chinese lanterns (Physalis alkekengi) are invasive perennial plants grown for their colorful and delicate orange pods, which, true to the common name, remind one of those paper lanterns sometimes used to decorate with an Oriental theme. Here's the problem with growing these plants: using rhizomes, they can easily spread out of control in your landscaping, causing you more headaches in landscape maintenance than their beauty and uniqueness warrants.
How to Get Rid of Chinese Lanterns
In the case of Chinese lanterns (as with other invasives that spread via rhizomes), eradication efforts must largely focus on the root system. Also expect to be battling this aggressive spreader for an extended period of time (but you probably already surmised that!), as you would, for example, the notorious spreader, Japanese knotweed. Here's what we recommend doing:
Don't Plant Anything Near Chinese Lanterns Until Eradication Is Complete
Until eradication is complete, we wouldn't plant anything else near the Chinese lanterns. You might even want to consider digging up and potting (temporarily) any existing plants there that are in too close a contact with the Chinese lanterns. This will accomplish two things:
- If you choose to continue using Roundup (many people won't use Roundup, but you mention that you have been), you can do so without worrying about accidentally killing your flowers. Roundup is a non-selective herbicide, so this is always a concern. Sometimes repeated sprayings are required (over the course of years) to achieve eradication for some of the tougher invasive plants.
- You can avoid having the lantern rhizomes getting all tangled up with the root systems of your good plants.
Keep Them From Spreading Further
To further isolate the Chinese lanterns and keep them from spreading any further, corral them with some kind of barrier. To use an extreme example, we discuss building a bamboo barrier in an article about containing bamboo. Different plant, similar problem.
Dig It out
Even if you do apply an herbicide as part of your eradication approach, you can still supplement it with other control methods. For example, let's say that, after spraying, the vegetation dies back. So far, so good. But you have to assume that at least part of the root system will live on to fight another day. At this point, you could begin trying to dig it out. Make sure you try to get every last scrap of root out of there, though, because, otherwise, they'll regenerate. To accomplish this, it helps to sift the dirt, so that you can go over it with a fine tooth comb.
Starve the Root System
Let's assume that, in spite of these efforts, new shoots still pop up. You'll have to take care of these as soon as possible, lest they send nutrients back down to the root system. The idea is to starve the root system over time. How you deal with the new shoots is a matter of preference. Some people would spray them with an herbicide, others would dig them out, still, others might try covering the recalcitrant shoots with something (such as a tarp) that would smother them, depriving them of sunlight—again, as folks might do to kill Japanese knotweed.
There is no magic bullet to use to control and/or kill Chinese lanterns. The best advice we can give is to employ a variety of methods (underground barriers, herbicide sprays, digging, smothering tarps) and to be as persistent as the plant is.
Guide to Poisonous Plants - Chinese Lantern. Colorado State University Website