What kind of weed is in my roses?

Question: I was about to start pruning my rose bush when I saw these things sticking through the mulch. I thought they were just regular weeds but it turned out they had a pretty large root system spreading around and right up to the base of the rose bush. The roots seem to grow more horizontally  than vertically and were only a couple inches deep in the soil. When I’ve unearthed the leaves, there’s a pungent smell. The underside of the leaves near the stems have purple on them. The biggest ones are only 2 inches high but a single root I found was like 8 inches.  I’m not super familiar with rose roots so I don’t want to accidentally mistake one of those for the roots of these when I yank it out. Can you tell me what these are and how to safely remove them without disrupting my roses?

responder: Jeff C, Master Gardener Volunteer Replied April 19, 2023, 8:56 PM EDT
response: Hello there and thank you for using Ask Extension.    It is very difficult for me to identify the weed, but you have provided me with some clues.   My guess is that it is spreading from a nearby plant.  You mentioned that it is aromatic.  Does it have square stems?  If so, it is likely to be in the mint family.  Mints are know to spread by rhizomes (underground runners) throughout their area.    As far as managing it, I would recommend cultural controls, that is, pulling it.  The roots of the rose are quite different from what you are describing. They are very strong and appear almost woody.  They are described in the literature as "fibrous."  Here's what they look like.  https://www.rose.org/single-post/2018/04/28/your-roses-roots  You will need to be careful in pulling out these invasive roots, because it is possible to damage your rose.  But according to the research I did, using a hoe is not recommended.  Hand pulling would be fine.  Here's a nice article about caring for roses that includes dealing with weeds.   https://ipm.ucanr.edu/PMG/PESTNOTES/pn7465.html  It would be best if we could positively ID the plant that is creeping into the rose's territory.  This would help in managing it in the long term.  Once the leaves get bigger, I might be have a better idea, but I suspect you want to get rid of it as soon as possible.    My recommendation is to hand pull the "weed."  Try to follow the weed's roots back to the parent plant.  It must be nearby, either in your own backyard or your neighbors, if this rose is located near a property boundary.  If you are able to determine the parent plant, let me know, and I can give you some better suggestions on how to exclude it from invading your rose bed.   Good luck.

responder: The Question Asker Replied April 19, 2023, 10:05 PM EDT
response: Thank you for your help, especially for showing me what rose roots look like so I can be careful. The hoe hasn’t been very effective due to the length/shape of the roots, so I definitely agree.  I will try tracing the roots and see. I’ve tracked them approximately 3-4 feet but they don’t seem to be connected to anything yet. I will continue to look. The only immediate surrounding plants are the roses, and a sand cherry shrub. In the meantime, I managed to get some better pictures (sorry for the first one, they’re just so tiny it’s hard to focus on them). I haven’t found a match to a mint species based on appearance but maybe that’s just because these leaves are young (I haven’t found any more mature patches and these just started springing up). One of the pics you can see the purple and greenish root exposed. It’s large in comparison and pretty strong.  The odor, for clarification, is more sour, like an onion and doesn’t come up unless I dig the root out. I don’t think the stems are square.  I’ll let you know if I need help after finding the source of the roots but otherwise if this new info brings anything to mind please let me know. I just moved in over the winter here so I’m finding some very weird things in this house’s backyard haha.

responder: Jeff C, Master Gardener Volunteer Replied April 20, 2023, 6:07 PM EDT
response: Hi again.   It looks a lot like a mint species.  The plant will have to get a little taller for the square stems to become obvious.    There are mints, and other plants, that are aggressive ground covers.  That means, they spread aggressively.  Unfortunately, they are challenging to control.  Digging up the root and rhizome is effective, but it is something you need to do pretty regularly.   The  University of California document I sent you earlier, does mention some chemical controls.  But before you try that, you should get a better idea of what you are dealing with, meaning what is the plant, and what is the extent of its growth.       Feel free to contact me again with some future photos and/or information.    Happy spring!  Hopefully you'll discover some fun plants.