The biggest thing to be concerned with Rugosas is soil pH, they're very intolerant of alkaline soil. Test your soil & adjust pH to below 6.0, mid 5's ideal, if needed. This is assuming that they are going to be own root which is how Rugosas are usually sold

wirosarian is correct. If the pH is too high, you'll have chartreuse foliage and not enough chlorophyll for best growth and bloom. Otherwise, just dig 3" of manure (preferable) or compost into the upper 10-12" of soil.

Dagmar is a good choice.

Just a quick question. How large is this space where you plan to plant 20 Frau Dagmar's? I ask as once established and assuming the graft is buried, she tends to go own root and suckers like crazy. 20 plants is a large number and I hope you're planning for the eventual size and space this many suckering Frau Dagmars will consume.

Thanks everyone for your responses!

the morden man - to answer your question... I did think about that as I do not want the plants spread beyond the hedge area. One side of the hedge is lawn so I figured the lawn mower would take care of any suckering plants? The other side of the hedge I was worried about (it will be mulched right next to these plants, but the hedge is basically creating a border for an area where I will be planting a few fruit trees - a few feet out from the hedge) but after speaking with a woman from the place where I was thinking about ordering, she said that fru dagmar doesn't spread as much as some of the other varieties and that i shouldn't be 'too' concerned about it...

What do you all think? I really don't want to be dealing with constantly needing to keep these shrubs in check - I had planned on burying a hardware cloth fence about 12 inches deep on the non-grass border side to keep out voles (so out of the fruit tree/garden side) - maybe I should consider adding some type of barrier as well to keep the roses contained? Like plastic edging? It'd be easy enough I would think since I'm already digging the trench for the fence...

thanks again for all the input!!!

Mowing will work fine on the lawn side. You can buy plastic root barrier 16" deep to set on the unmowed side. Roots that produce suckers probably don't grow that deep.

If you are ordering grafted roses, you can set the bottom of the graft right at soil level and this will prevent suckering. Canadian producers such as Hortico, Palatine, and Pickering produce grafted bare-root roses which are a good value for US consumers.

Normally most of us recommend burying the graft just slightly for zone 6 gardens, but not for winter-hardy roses that sucker.

What spacing do people suggest for a hedge of Dagmar? Three feet?

In my experience, Frau Dagmar root suckers with the best of the Rugosa's. To give you an idea, I planted a couple of them to frame the opposite corners of the bottom edge of a kidney shaped flower bed in my Mom's garden. They stay a nice compact 4ft tall, but have suckered so extensively in the last 5-6 years that they are basically about 10-12 by 8-10 ft now in terms of length and width.

That was from a single plant in each corner... I've offered to remove some of the suckered plants, but Mom likes them like this as they fill in the area nicely, so we've let them sucker unchecked and they are a sight to behold in full bloom.

I'm not sure a root barrier like plastic edging would stop it. You'd need to go deeper than 6" down and would need something stronger.