If you are willing to be tedious, you can control the grasses with round up and a paint brush. Simply get your sloution and paint a couple fo grass blades on the plant. Do not touch nayhting else green with the round up.

here is my method of removing grass in my thick daylily bed. you need to --if you are not over 200 lbs you can sit on an overturned 5 gallon pail and then use --1) pair of plastic gloves, put on hands over skin 2) on one hand, put on a fabric glove over plastic (be sure they are new with no soil on them) 3)spray the finger tips of the fabric glove with round-up and then gently drag the grass leaves/stem in your hand so your finger tips will get the grass wet with the round up. rewet finger tips as needed. works for me with quack grass in Michigan. For horsetail in the beds, use the same method but the poison ivy/shrub killer. be sure to write 'round-up' on the gloves to know which one to use--and not to use them when working around other plants. (if only a few, a plastic bag on your hand and hand paper towel in your hand works too.) The brush idea works great if the brush doesn't drip and you don't dump the 'container' over on the plants-been there done that!!

I have used a product quite successfully called Poast. This product is available under many names. The last batch I got I just did a search on Ebay for Poast and it came up with other products that use the same chemicals. These seem to work well too. It is very slow to respond. I sprayed this spring and it took about 4 weeks to kill the grass. What I like about it is that I can spray it right in the middle of a flower or bush and it will kill out the grass. You might get a quicker response by repeating the spraying in two weeks. I have not had it kill any flowers yet but I would be careful around grasslike plants.

Long term, your best bet is a thick layer of mulch. Lillies and iris will have no problem growing up through 3 inchs of pine bark or similar covering but it will keep 99% of grass seed from germinating. Hire a neighborhood kid for a one time pulling and then pile it on.