Whoever told you that ornamental grasses as a whole are not perennial, and won't survive out there in the North Shore, I full of manure!!!!!!Obviously, they are not willing to find the right grasses and grow them properly. How were the grasses planted? In what direction were they facing( ie North, south, east, west), and what were they palnted in? How were they cared for during their rest time, and throughout winter? These are thing that need addressing before asking what happened to your grasses. I am sure myself as well as others will fill your head with helpful info. Good luck, and bring the info....

All planted in the ground, most on the West side of the property. I believe that most of the ones which did NOT survive are facing West. Three of them never came up at all. However, the one fountain grass which thrived is facing the same way, but is planted further north than the others on that same West side of the house. Two others (zebra grass) which seem to be filling in fairly well, also face West but are in the yard, which is the East side of the house. Two other miscanthus, which are on the South side of the house seem to be coming in. Two fountain grases which are on the North side of the house have only a few pieces of growth. None of the grasses were mulched. The ones which are doing well, in all areas, seem to be the ones which get less sun than the others.

Those who tell you that those grasses are not perennials are more than likely smoking some of what they are planting. I have had grasses in my zone 5 garden for now over 6 years and have not lost one. One thing to remember is that..first year they sleep, second year they creep, third year they leap. Also, are you cutting them back in the spring ? That allows sunlight into the center and helps them grow and come back a bit earlier. Also they do best when planted in what I refer to as "Lousy Soil". Too much fertilizer, too rich a soil, and too much water will cause them to flop, but won't stop them from returning. The only grass you mentioned above which is marginal for me is the Japaneese Blood Grass. Check the link below to see how my grasses come back for me in zone 5.

Blackie

Here is a link that might be useful: My grasses

My first thought reading your post regarding ornamental grasses not being perennial plants threw me back a ways.

As answered by others ornamental grasses as a group fall into perennial and not perennial.

As with most all plants the zone or climate temperature ranges are the most influential in determining perennial or not. Okay throw in a little sunshine as well.

In your zone if it is Z7, I would think even Imperata cylindrica "Red Baron" would be a perennial plant. Might need a little winter protection. I have had Red Baron come back in Z4b  5. Not on a regular basis but I never made any real effort to protect it during the winter.

Jake

Like others have told you, you can ignore the b.s. that grasses are not perennial.

Cultural needs for most grasses, including the ones you planted, are not that demanding and, from your descriptions, their site whould have met their requirements. West-facing is fine, especially for warm-season growers like Miscanthus and Pennisetum. Crown rot overwinter can damage or kill a plant, but you did not mulch, leaving one question: how well do their sites drain in winter? Planting after October (on L.I.) would be a no-no for grasses, but I infer you planted before then. Soil?, as one respondant queried. Do you have problems growing other perennials, shrubs, trees? Have you dug up any of the grasses to examine its root system?

L.I. climate is ideal for most grasses. Possibly the plants you bought were less than of robust health (afterall, you were gravely misinformed by your nursery as to classification of the grasses you bought). All in all, you have presented a mystery.

I think that two of the grasses facing north are Pennisetum, and they seem to be doing well. The fountain grasses are a mixed bag. One of them is fantastic - huge, three times the size it was last year, whereas the other, roughly in the same area, has a few blades, and no more. Another two or so fountain grasses are okay, but a couple died over the winter (either that or the gardener pulled them out as "weeds" which he has done with a LOT of my plants!).

I planted three Cortadera in the Fall, which arrived already cut back. None of the three came back, and yet they are in the same vicinity as the fountain grass which is thriving. The two cortadera which I bought in full bloom, and about three feet tall when purchased, have developed several blades around the perimeter of the cut back plants, but nothing has come out of the middle at all.

No, I have not dug any of them up, although I can dig up the three which never came up at all ( the cut back areas are still present at ground level). As for other perennials, no problem. I am growing rudbeckia, echinea, hellenium, golden marguerite, gaillardia, shasta daisies, lilies, choreopsis, the usual ubiquitous daffodils and tulips, and many more. All are thriving (again, except for those which disappeared thanks to my gardener, and he is now not allowed to touch anything, so I am doing a lot of weeding!)

I am growing a number of fruit trees, and blueberries, raspberries, blackberries, figs, all with success. My trees, conifers, hydrangeas (I have loads of them), roses, are all happy. It's only the darn grasses!