Ground cover and/or mulch for a rain garden? And suggestions for new native plantings? - Ask Extension
Hello,
I'm writing today to ask how to handle ground cover and/or mulch needs in my rain garden of native plants (as well as to seek suggestions fo...
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Ground cover and/or mulch for a rain garden? And suggestions for new native plantings? #926674
Asked March 24, 2026, 4:06 PM EDT
Hello,
I'm writing today to ask how to handle ground cover and/or mulch needs in my rain garden of native plants (as well as to seek suggestions for new native plantings). My rain garden was planted about 8 years ago, and includes a thriving beauty berry near the down spout, and blue dogbane and brown-eyed susans in the sunken middle. I used to have some cone flower on the side away from the down spout, but unfortunately most of the cone flower has been choked out (which makes me sad, as I would like the cone flower to thrive).
There is another bush on the other side of the rain garden, away from the down spout. It may be arrowwood, but I'm not sure. A naturalist who was in my yard in November thought it may be wild blueberries, but I don't think that's the case, as it's never produced any blueberries. There is grass (maybe Shenandoah red switchgrass?) on the back berm of the rain garden.
I'm curious what kind of ground cover/mulch, if any, I should put down to help these native plants thrive, and to choke out weeds/invasive vines that often threaten the garden. I would also love to plant more cone flower, and add some bottled gentians, and/or lobelia in the rain garden, but I fear the dogbane is so thick/crowded in the middle now that it may choke out any new plantings. Can you recommend where I may plant some other natives that may add some color and texture to the garden?
I'm attaching pictures I took this past October, when the garden was in full bloom (and wild and wooly!), in case they may help.
Thank you in advance for any/all advice you can provide. Please note I live in DC near PG County, but I was told to use this Maryland contact form for my DC gardening questions.
Prince George's County Maryland
Expert Response
Hi Melanie, how good that you have a rain garden.
Let me start by referring you to a very comphrensive publication from Maryland Extension, Rain Gardens Across Maryland;
https://extension.umd.edu/sites/extension.umd.edu/files/publications/Rain-Gardens-Across-Maryland.pdf Since your rain garden is already in place, you won't need much of the information at the beginning portions on how to site and constuct your garden, but this will be a good resource for you in maintaining and perhaps enhancing your garden.
For mulch, there's no unusual requirements for a rain garden, and any common organic mulch will do fine, though you should avoid lightweight mulch and flat wood chips because they will float when it rains.
I myself don't have a rain garden, but I have several large beds of (mostly) native plants and I have found that, as the plants mature, I need virtually no mulch. For one thing, as noted in the rain garden publication, you want to cluster your plants, which minimizes the amount of open soil that otherwise would need mulch. Also, I leave all the plants standing throughout the fall and winter, and only in early spring do I cut down the dead plant material from the previous year. I let the dead material simply fall to the ground, and it serves as mulch. Easy and free!
As to your amsonia (dogbane), it does grow very dense, but it doesn't spread outwards so I wouldn't worry about it crowding out other plants--just give it its own space. If your plant(s) are flopping, they benefit from pruning in the spring. Here is more info on growing amsonia from the Univeristy of Wisconsin, https://hort.extension.wisc.edu/articles/willowleaf-bluestar-amsonia-tabernaemontana/
For additional plants, the Maryland publication has an extensive list of suggestions for both herbaceous plants as well as grasses and sedges and shrubs. From this list, plants I have had success with include Beebalm, Joe Pye Weed, Swamp Milkweed, Turtlehead, Narrow-Leafed Moutain Mint (though it does spread), and Cardinal Flower (total hummingbird magnet!). I suspect any of the items on this list would do well. I observe that coneflower is not on this list, and perhaps the problems you had with that plant had less to do with overcrowding and more with excessive moisture--they require very well drained locations.
One final note, the District of Columbia does have its own Master Gardener program, and they are available to answer questions, https://sites.google.com/view/dcmastergardener/ask-a-mg-online-service?authuser=1
I hope this is helpful, good luck with your rain garden.
Bob
Let me start by referring you to a very comphrensive publication from Maryland Extension, Rain Gardens Across Maryland;
https://extension.umd.edu/sites/extension.umd.edu/files/publications/Rain-Gardens-Across-Maryland.pdf Since your rain garden is already in place, you won't need much of the information at the beginning portions on how to site and constuct your garden, but this will be a good resource for you in maintaining and perhaps enhancing your garden.
For mulch, there's no unusual requirements for a rain garden, and any common organic mulch will do fine, though you should avoid lightweight mulch and flat wood chips because they will float when it rains.
I myself don't have a rain garden, but I have several large beds of (mostly) native plants and I have found that, as the plants mature, I need virtually no mulch. For one thing, as noted in the rain garden publication, you want to cluster your plants, which minimizes the amount of open soil that otherwise would need mulch. Also, I leave all the plants standing throughout the fall and winter, and only in early spring do I cut down the dead plant material from the previous year. I let the dead material simply fall to the ground, and it serves as mulch. Easy and free!
As to your amsonia (dogbane), it does grow very dense, but it doesn't spread outwards so I wouldn't worry about it crowding out other plants--just give it its own space. If your plant(s) are flopping, they benefit from pruning in the spring. Here is more info on growing amsonia from the Univeristy of Wisconsin, https://hort.extension.wisc.edu/articles/willowleaf-bluestar-amsonia-tabernaemontana/
For additional plants, the Maryland publication has an extensive list of suggestions for both herbaceous plants as well as grasses and sedges and shrubs. From this list, plants I have had success with include Beebalm, Joe Pye Weed, Swamp Milkweed, Turtlehead, Narrow-Leafed Moutain Mint (though it does spread), and Cardinal Flower (total hummingbird magnet!). I suspect any of the items on this list would do well. I observe that coneflower is not on this list, and perhaps the problems you had with that plant had less to do with overcrowding and more with excessive moisture--they require very well drained locations.
One final note, the District of Columbia does have its own Master Gardener program, and they are available to answer questions, https://sites.google.com/view/dcmastergardener/ask-a-mg-online-service?authuser=1
I hope this is helpful, good luck with your rain garden.
Bob
