A couple of considerations to think about before I answer your question:
-"is going against a fence." Is the soil going to be against the fence? If so, this will probably cause problems to the fence, depending on the type of fence.
-Is the bed 7 feet wide including the stone and there is 5 feet of soil width or 5 feet wide including the stone? If it's only 3 feet of soil, you might want to reconsider, since 3 feet is a pretty shallow bed and it will be more difficult to avoid having a single row of plants, especially since the back of the bed is against your fence which you may need to access to paint, repair, etc. I like having really deep beds since I can have more layers of plants so there is most always something blooming as well as lots of interesting foliage. I think that my shallowest bed is 6 feet deep and they are mostly much deeper. I wouldn't worry, except a stone bed is difficult to move if you want it deeper after a few seasons.

In general raised beds are better drained than regular garden beds. They warm more quickly in the spring, but may freeze more deeply during the winter. If you have the narrower soil width (3') you may find that your plants are more prone to freeze and thaw, especially those planted near the edge, though the stone may be enough to mitigate this, especially if it is mortared.

You will want to be sure to have lots of organic matter incorporated into your soil and the surface mulched in order to help keep soil moisture even, since clematis need moist soil, and you may need to water a bit more often than if it were a regular in ground bed. If you plant your clematis at least 6" deep, this will also help prevent drying out and freeze-thaw problems.

Hi nhbabs,
Yup, I read a lot on here before I started on the wall.. the actual planting area is going to be 5 by 18 and there is a row of stone against the fence too so theres no rotting... in retrospect, I wish I had used a less wide stone as I can see that the clematis are going to have to trail over the stone before they hit the fence but its what matched the existing stone we have at our place. If the fence needs any repair, my neighbour is ok with us doing it on his side as there's about an inch or 2 away from fence along the length. I'm worried about stepping on plants in the front to access any of the clematis at the back row though.
The entire wood fence is being covered in the vinyl green wire that I learnt about on this forum.
What can I do right now to avoid the freeze and thaw near the edge. There are not being mortared as they are only one stone deep with the cap, (11 inches). The stone is also one foot deep. But its not too late yet to do it 2 stone deep although my husband might have a freakout. There's space in the center of the stones which I guess is what gets filled with dirt...Is there something else I can fill them with that would help with the insulating factor? Besides lots of mulch in the fall before winter... anything else?
I'm in bruce county near the lake so we get lots of snow.
I have a feeling that we'll have to rototill the existing soil as its pretty compact.

Yup - rototill or dig the existing soil and add lots of compost or well-composted manure; lots of organic matter will help keep moisture even. Since you get lots of snow then you won't have to worry much about freeze-thaw if it's at least the foot deep that your bed is. I'd probably not plant any borderline hardy clematis, though. Once you put in your soil, put in stepping stones in places that you might need to walk so that you don't have to worry about compacting soil or stepping on plants.

Just an update to show off the very slow progress of my raised bed. It really does take time to grow beautiful clematis
2 years later and we still haven't put in stepping stones yet primarily because I haven't decided what to plant in the raised bed yet. Excuse all the weeds and the lilies, we used the bed to get them going.
I did wave petunias in whites and pinks last year and it was gorgeous. But with the very cool late start to warm weather here by the lake, I decided not to plant this year as we were still getting frost in June.
Hard to believe Huldine was a 6 inch plant in 2012 july.
I know I tend to plant close together. Jackmanni and General Sikorski which was pretty much dead and 2 bucks 2012.
Still needs to fill out a little in middle.

Anyone has any suggestions on what to plant in the bed? I have a few Clematis Bijou and Filigree ready to plant but they were super pricey and its going to take a lot more of them to plant.

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Your clematis look wonderful.

Looks like you have a nice sized space in the bed. Do you want the plants there all to be the same or mixed? I have delphiniums, hardy geraniums, dianthus, penstemons, columbine, and daffodils with my clematis. My bed is long and narrow along my neighbors chainlink fence.

I kinda want roughly the same kind of plants but they have to be low so as to not block the clems. This front section was planned to have no yellow or red, just shades of purple pink and mostly white.
I'm stumped! I'll either end up with petunias again next year or I really got to start planning and budgeting for Hostas which are killer expensive here.
I water once a day on a soaker hose so I'm pretty sure anything bulb like daffodils and lilies will end up rotting out.

I suggest you determine how tall you want your plants to be and google annuals and perennials in that range and choose ones that meet your conditions and color scheme. You could use your purple, pink, white theme with short 18-24inch perennials. Salvia 'Caradonna', hummelo stachys, perennial geraniums, short shasta daisy, dwarf bell flowers, platycodyn or campanula, dianthus, nonflowering stachys, short penstemon, short nepeta, short hydrangea 'Bobo', etc. Any of these can be masses though I like to use a mixed bed so there is something in bloom from summer to fall.

Many of the above can be started from seed via wintersowing, the easiest and cheapest propagation system for perennials that I have used.

If you want annuals how about short cosmos, easy from seed; zinnias, many short varieties in several colors bloom from spring until frost, annual salvias, etc.

There are so many choices. Check out the images pages when you goggle plants for ideas.