shelli, if you add your location next to your zone in your i.d. line, people will be able to learn from and help you because they can relate to your experiences through theirs. i think the question you have is not are these plants zone hardy but are they hardy when planted in raised beds. 18" is not terribly high but i don't know the answer. i think there is some rule about plants surviving in raised planters or beds if they are 2? zones hardier than your zone. but i've been meaning to look that up for awhile myself. I can tell you that my sedum in a container 2' H- survived our z. 5 winter fine last yr. and my hakonechloa planted on the sloped walls of our 'chasm' also has survived for years. best, mindy www.cottonarboretum.com/

At my last house I had raised beds - 4' wide by 12-20' long with wooden sides about 1 1/2 foot tall. Over two or three years we built 8 of these large beds plus several smaller beds for perennial crops like stawberries, rhubarb, and horseradish. For that situation, there were several advantages. It allowed us to have flat areas on a hill; we terraced with rock walls and put the beds on those flat areas, surrounded by woodchips for mulch, so there was no weeding at all. The beds were sunk about a foot below the grade, and we had to sift the soil, which was shallow over fractured ledge, to get rid of all the rock, and then we filled the rest of the beds with composted cow manure, thanks to our local dairy farmer. So, we ended up with no weeds & great soil in flat beds from an area that started out mostly rock on a steep grade. Other pluses were sitting on the bed sides to plant, screwing trellises for beans, melons, cukes, etc. directly into the bed sides, and the ablility to plant early due to good drainage and early season warm-up. We also sometimes put plastic hoops over the beds, tucking the hoop ends inside the beds to hold them, to cover with spun-bond or plastic. On our strawberry beds, we put hinged wire mesh covers so the chipmunks couldn't eat the berries. Between mulch and the high organic content of the soil, we only had to water when it had been dry for a couple of weeks or more. Our current house had a pre-existing ground-level garden which we simply took over as was since the house needed a huge amount of work, so that's where our efforts and energy went. I miss the raised beds, and find that I have more difficulty with soil-living bugs like wire worms in my potatoes and cutworms crawling in from the surrounding field. I can't work in the garden as long since I have to bend more or sit on & scoot along the ground. (I'm no spring chicken!) The grass and weeds migrate into the veggie garden from the surrounding field, and the soil needs to be prepped in the fall so I can plant peas, potatoes, etc. earlier in spring since the soil stays cold and wet for much longer. There are two only advantages I can see to the ground level garden: it's easier to till with a machine like a big tiller or tractor if you want to be able to do that, and any crops that need winter warmth can be well mulched and will stay warmer in the ground. Garlic, which is a bit borderline as far as hardiness here, has better survival rates, and my leeks and root vegetables overwinter better with a thick layer of mulch when they are in the ground rather than in a raised bed. So, like Lisa, I will eventually have some of both, but with most of my garden as raised beds and a smaller part of it in the ground.

OK thanks Babs! I have a montauk daisy (planted by a previous owner) which is about 4' across, but I'd always been under the impression that it was made up of 2-3 smaller plants. I'm probably wrong. There are plenty of other spots at the school or at my house that I can use them. That being said, I do think the garden would work better as a slightly "overstuffed" space to choke out weeds, since it relies on very inconsistent volunteer help to maintain and got seriously overrun with weeds in the past few years. Any thoughts on placement?

Majority of perennials are grown in raised beds. My backyard is terraced. Hydrangea, clematis, peonies, spireas, lilacs, roses, lilies, stonecrop, columbines, poppies, ferns, etc. all survive Zone 4.