There are essentially two kinds of plant types - monocots or plants that produce single blades rather than stems and leaves (grasses, irises, most bulbs, etc.) and dicots or those with leaves and stems. Weed B Gon is usually intended for use on lawns - a monocot - so is also safe to use on ornamental grasses. It only affects broadleaved weeds/dicots.

Preen is a pre-emergent. It won't affect any existing plants but only retards germination/root development of seedlings.

Weed B Gon...well, I'd test that theory before using it, although if the previous owner got away with it, it should be OK. There are plenty of species of grass you can't use it on. Still, I'm not willing to give it a green light without knowing the exact species of ornamental and seeing that species on the label as being OK and wouldn't recommend using it without testing unless you have that assurance.

RoundUp will kill any green plant it touches that hasn't had a certain gene sequence inserted. Yours are not immune. Don't use it.

With my Zebra grass, a lot of manual effort is required. It's often best to inspect weekly and take care of problems as they develop. That little tree is easier to remove as a tiny seedling rather than wait until it's a sapling. Annoying, sure. But that's true of most problems, I guess.

Mulching will certainly help, as will application of Preen early in the season next year (although take a look at the weeds you actually get and match the correct pre-emergent to the correct weeds. I have been...well, less than impressed with Preen, let's just say, due to my weed profile). Reapply said pre-emergent when the shield runs out, which will be dependent on the pre-m and the dose used (my Prodiamine lasts 9 months, but that's the dose I use--and it's the maximum for the year).

Like any other summer-growing grass, these also benefit from a moderate feeding on-schedule. You can look up care online, or just ask and we'll outline the care and feeding strategy for you. This is already getting kind of long.

I think you'll have to do what Ken says: late winter/early spring, remove the big grasses (BIG job by the way), kill off the weeks, replant the grasses and mulch well. Then keep up with the weeding. It will be a small job if done once a week.

Weed b gone is a brand with multiple formulations available in concentrate and ready to use. If you are going to use the previous owners recommendation you must know the formulation (active ingredient names) and the concentration used.

That’s exactly right, pennlake.

Similiar situation with “ Round-up” - some products bearing this brand name don’t have glyphosate and are formulated for broadleaf weeds in cool season lawns.

Oh, yes, quite and thank you, I forgot to mention that and it would be a horrible mistake to make! WBG original versus CCO versus the one that kills brush would all have different and very, very disappointing results, potentially!

I'd tend to be very conservative in terms of chemicals used on ornamentals and know the species I'm dealing with (I can't get a read on it from the distance pic and probably wouldn't be able to up close; check with somebody who has the vision and time to do a Google pics search).

Hi all, thank you for the advice! It is much appreciated! @User, you mentioned feeding the ornamental grasses. Do you have any recommendation on what I should use and how I should do it? I'd be very interested in learning. A lot of the grasses are about 4 feet shorter than when we moved in. I have a privacy fence on the side of my yard and the grasses were a few feet taller than the fence when we moved in. Now, they are a few feet shorter. So I feel the previous homeowners had to have been doing something.

Unfortunately, I don't know the exact type of the grasses. I might hold of on the weed b gon. There are tons of varieties of it and I'm not sure which to use. I don't really want to kill one by testing!

I have Itises so im very limited as to what grass killer that I can use safely around them. i did find one, tried it, and evaluated it. Ortho Grass-B-Gone killed the grass and did not affect my Irises…that im aware of anyway.