The tallest 'Cosmopolitan' I've seen in my zone was 8-9' to the top of the tallest plume. I doubt if the foliage was much taller than 6'. If you're buying from a nursery, you should ask what the height of the foliage will be, and then the height of the plumes above the foliage. There are ornamental grasses with plume heights which double the foliage height. In my experience, the height range listed on nursery tags, and in catalog copy, are to the plumes. In some cases, this works, because the plumage is so dense, it acts as a screen, but in others, it is not.

Research research research.

Keep in mind, many mature sizes quoted are based upon ideal conditions. Many warm season grasses require a zone warmer than 6 to reach maximum cultivar dimensions. The length of the growing season is a factor in achieving that size.

Your Cosmopolitans aren't nearly at their full potential if they are only one foot wide. They will get four feet wide at least. And they should get about six feet tall. With plume maybe eight. If you really want a screen, Miscanthus Giganteus will do the trick. Mine are already ten feet, and in plume will be about fourteen. Any chance you can put a line of them behind your Cosmopolitan? They are quite upright, and make a great backdrop for other grasses. And other grasses hide their bare legs.

Cabaret and Cosmopolitan are in the group of Miscanthus called sinensis var. Condensatus, and are only hardy to Z6. So more southern states would probably obtain greater heights than you would.

But it is a beautiful grass, and in a few more years will be outstanding. Are you watering and fertilizing them? They don't need much, but if yours are only one foot across I would give them a little fertilizer.

Polly

I've got 'Centreal Park' which is an all green verson and it's 6 feet tall right now and the base is almost 2 feet wide in it's third year, plus I've moved it twice

if you water alot, it will grow like a weed. also plant will peat moss or other organic material if the soil is clay

dunn - Even at a zone less than yours, it seems like my 'Cosmopolitans' should be closer to the 6' you mentioned than the under 4' mine are. "Research, research, reasearch" is exactly what landed me the Cosmos! (LOL) Sadly, there seems to be a real shortage of ornamental grasses locally and even the folks at a nursery I really trust couldn't tell me whether the listed heights of various grasses included plumes or not!

pollyny - I actually poked around here for Miscanthus Giganteus and couldn't find any. I suppose I should have held out, mail ordered some for next spring, and not bought the zebras. Wonder if the nursery will take returns?? Hmmmm .... I'll still have to move my Cosmos, which are too near the property line to accomodate anything planted behind them. I'm not giving them any extra TLC (I have a rather Darwinian approach to gardening, I guess!). For some reason, I thought grasses did a bit better in slightly "lean" conditions anyway?

noki - Did you buy your 'Central Park' locally or mail order? Sounds like another vote for watering my Cosmos. Now I'm REALLY torn about what to do with them ... and the zebras!

I think when grasses are young, you need to water, and fertilize. For the first couple of years anyway. After that they do pretty well on there own, however, I feel they still do better with water and fertilizer. Not huge amounts, because that can make them flop, but some. If your plants are only a foot wide after three years, I would think they need some supplemental watering and fertilizer. Even Miracle Gro as you water.

I wouldn't give up on the Cosmopolitans yet. Try to give them some TLC, and see what they do.

I'm not a fan of Miscantus Zebrinus. It's floppy for me. I think there are much nicer varieties out now.

And here's a good place to purchase grass. I realize it's hard to find a good amount of variety locally often.

http://www.earthlypursuits.net/Merchant2/merchant.mv?Screen=CTGY&Store_Code=EPI&Category_Code=MISC

oldgranvilleplace:

i have a cosmopolitan that sounds like yours and i have had it for about 6 yrs. i believe it is because it is not in total sun... but rather in partial shade... it does get 5 or 6 hrs of sun a day and in most cases that is adequate for sunlovers but we all can think of perennials that do better in total sun. i am about to move it .... just waiting for spring to come around again.
i also have some miscanthus giganteus i would be glad to trade with you for some other kind of grass. i can send a decent sized start though the more i send the higher the postage. drop me an email if you are interested and we can talk about it ok? thanks!

Sue
"The one thing all gardeners share in common is a belief in tomorrow"

Hi oldgranvilleplace. I'm curious how the zebra grass is working out? I'd also like to throw in my 2 cents on the Cosmo. The tallest I've seen Cosmo here in zone 8, is 7 ft of foliage and 2 ft of plumes. Thats with irrigation and feed. Climate and growing conditions can have a huge impact on mature size, but don't give up on them! Tey are beautiful and stand to their height well, vs a Zebra grass that will tend to flop at maturity, especially after a good soak.

Best of luck with them!

I grow Cosmopolitan grass in Zone 5a. The first year it was around 4 to 5 feet high without blooms. It developed into a 6 foot diameter stand that is closer to 5 feet on bad years and 6 feet on good years without the blooms, which come on in September. My Zebra grass might be a sport off the original strain, as it gets 10 feet high with blooms instead of the 7.5 feet high as widely described.

Just a little more info. (is there ever too much?)I can tell you that there is 'zebra grass' and Miscanthus 'Strictus', same plant 2 different varieties. 'zebra grass' tends to be of a floppier nature, whereas, 'Strictus' is more erect. I have a 'Strictus' that was planted 2 years ago it is 6ft tall (foliage) and 2-3ft wide. It gets alot of wind and 3/4 sun, a good weekly watering and slow-release fertilizer in the spring. It's doing great and grows as I hoped and expected it would. I hope this helps!!

fwiw, I really really really like Cosmo.

Bought 4 of them a couple of years ago. From a good reliable nursery.

Only one turned into the 'real' Cosmo. One is a very nice grass, same width leaf with very similar markings, very robust with terriff blooms, but the foliage tops out around 5 feet or so. The other 2 turned out to be not good garden plants at all at all....

sooooo, with mailorder & purchasing the smaller size plants one can have trouble.