Perennial question - Ask Extension
My pestimin has not done well the last 2 years. Can someone look at the attached picture who may be able to diagnose the problem?
Knowledgebase
Perennial question #930102
Asked April 30, 2026, 12:15 AM EDT
My pestimin has not done well the last 2 years. Can someone look at the attached picture who may be able to diagnose the problem?
Larimer County Colorado
Expert Response
Hi Shari,
Tell me more about the cultural care of the penstemon. Are they in a wet area? Are they on drip irrigation? Do you clean up the leaves in the fall or spring?
It looks like it's linked to water (too much?) and that there might be some opportunist insects feeding on the foliage. Do you see any insects if you removed some of the blackened/brown foliage at the base?
Tell me more about the cultural care of the penstemon. Are they in a wet area? Are they on drip irrigation? Do you clean up the leaves in the fall or spring?
It looks like it's linked to water (too much?) and that there might be some opportunist insects feeding on the foliage. Do you see any insects if you removed some of the blackened/brown foliage at the base?
Thank you for answering my question. The penstemon are on a drip system and we do not see any bugs. This began last summer. The stalks also have brown spots on them.
Sent from my iPad
Sent from my iPad
On Apr 30, 2026, at 8:18 AM, Ask Extension wrote:
Hi again,
Is the area wet? How often did you run the drip last summer? I realize that you're probably not running the irrigation currently, but is the area wet?
I would cut back everything now, remove any brown/black leaves, and pull the mulch away from the base of the plants. Check the irrigation system to ensure there isn't too much moisture being held on the crowns of the plants. Penstemon are very waterwise and once established, only need occasional watering.
You don't need to fertilize. The new growth may have also been damaged by an opportunistic insect this spring. Do what you can to adjust the cultural conditions of the plants.
Is the area wet? How often did you run the drip last summer? I realize that you're probably not running the irrigation currently, but is the area wet?
I would cut back everything now, remove any brown/black leaves, and pull the mulch away from the base of the plants. Check the irrigation system to ensure there isn't too much moisture being held on the crowns of the plants. Penstemon are very waterwise and once established, only need occasional watering.
You don't need to fertilize. The new growth may have also been damaged by an opportunistic insect this spring. Do what you can to adjust the cultural conditions of the plants.
Yes we do clean up the leaves in the fall
Sent from my iPad
Sent from my iPad
On Apr 30, 2026, at 8:45 AM, shari Heymann wrote:
Thank you for answering my question. The penstemon are on a drip system and we do not see any bugs. This began last summer. The stalks also have brown spots on them.Sent from my iPadOn Apr 30, 2026, at 8:18 AM, Ask Extension wrote:
Yes, I'm recommending that you cut back everything now. This should encourage new growth.
Limit how much water the plants get and pull away the mulch.
Limit how much water the plants get and pull away the mulch.
Thank you
Shari
Shari
On Apr 30, 2026, at 9:07 AM, Ask Extension wrote:
