Hello Kathleen,

Mahonia repens generally likes dry'ish shade, so let me ask a few questions to sleuth this out:

• How long have the Mahonia been planted there?
• How have they bloomed in the past?
• How close does the sprinkler system deliver water?  I.e., how close is a lawn?
• Can you send me a photo of them in their setting under the maple, including surrounding lawn?

Best regards,

Mari

Thank you for getting back to me so quickly, Mari!  My husband and I moved to this house in west Arvada about 18 months ago so I don’t know how long the mahonia has been in the ground but I suspect it was planted in around 2000 when the house was built.  There is a weed suppressing woven cloth-like material under the rocks which I think impedes the spread of the mahonia.  I suspect I should remove it but am not sure.  We moved here Virginia with it’s very different climate and soil.  I am still trying to learn how to maintain our lovely yard.  I like the mahonia-it reminds me of the holly we left in Virginia.  

I have attached some photos.  I hope they help you diagnose our problem.  Our house faces east, by the way, so the mahonia gets morning sun.  I don’t think the sprinkler spray reaches as far back as the brick of the house.  

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On Apr 8, 2021, at 8:59 AM, Ask Extension <<personal data hidden>> wrote:

Hello Kathleen,

Thank you for the additional information and the photos.  Based on what I see in the pics, the Mahonia has some scorch/winter burn, which often is due to lack of moisture.  CSU is no longer recommending weed fabric (a long-standing landscaping practice), because after a couple of years, the pores in the fabric become clogged with dust/soil which prevents water from flowing through, plus provides a good medium for growing....weeds!  The rock "mulch", also a favorite landscape material here can interfer with air and water flow as well.  

Management recommendations:

1. Conservative approach:  Remove the rock mulch from beneath the dripline of the mahonia, as well as the other shrubs in the bed.  Remove the weed fabric from at least the same area.  Apply a 3-4 inch organic mulch layer (compost, shedded bark, etc) under each shrub, keeping mulch 4-6 inches away from the trunk/crown.
2. More aggressive approach that will make your plants happier in our compacted clay soils:
   1. Remove all the rock mulch and all the weed fabric.
   2. Replace it with the 3-4 inch layer of organic mulch (shredded bark, wood chips, gorilla mulch), keeping the 4-6 mulch-free zone around the trunk or crown.  The organic mulch will moderate soil/root moisture and temperature, and will add organic matter to the soil over time as it breaks down.  With the east-facing exposure, the house should keep the mulch protected from being blown away by our winds (the major risk of this solution).
   3. If you don't find any drip-irrigation hose under the rock mulch/fabric, you might consider adding it on a zone that you can set to water as deeply and infrequently as possible.  OR, just hand water monthly to a soil depth of about 12 inches to hydrate the root zone, including in dry winters.
   4. Being a native plant, the Mahonia should not need any fertilizer.  I can't tell what the other dormant shrubs are, but if they are natives, they won't need fertilizer either.
   5. Without the limitation of the weed fabric, the Mahonia will spread over time to fill the area as an awesome 4-season ground cover:  evergreen, bright yellow blossoms, blue berries.  It is one of my favorite natives!

References:

• Mahonia (Berberis) repens (note in the pic that in its native habitat, M. repens has pine needle mulch)  https://coloradoplants.jeffco.us/plant/details/584
• Mulching  https://cmg.extension.colostate.edu/Gardennotes/245.pdf
• Colorado Gardening:  Challenge to Newcomers  https://extension.colostate.edu/docs/pubs/garden/07220.pdf
• Index to Online Gardening Publications  https://cmg.extension.colostate.edu/gardening-resources/online-garden-publications/

Welcome to Colorado!  We have many resources to help folks learn how to deal with our crazy soil and weather.  Feel free to use Ask Extension, or to contact Jefferson County Extension Horticulture Directly.

Master Gardener Hotline <personal data hidden>, <personal data hidden>

Plant Diagnostic Clinic (Diagnosis, Plant ID, Insect ID)<personal data hidden>, <personal data hidden> 

Best regards,

Mari

Excellent!  Let me know what follow up questions you have.

M