Are you talking about wet roots (damp soil) or wet canes? I'm not comprehending how the trellis affects the moisture level.

Roses do not like to sit in standing water and they do need adequate drainage. Is the trellis part of a structure in which the roses are planted, and does it have drainage?

if they are in ground that is too wet I'd suggest building some raised planters by the trellises for them to grow in. That way you'll still be able to put them on the trellis but they'll be a soil that drains properly so the roots don't rot.

Or, several French Drains. The water comes from somewhere. Determining where and trying to mitigate the issue will likely be the most expensive, but most successful in the long run, unless you have an underground river where you're trying to grow them.

R. Palustris is the species known for tolerting wet conditions, but it isn't the kind of rose you are wanting there. And, no, I don't know of anyone ever trying it as a root stock. Kim

Here is a link that might be useful: The Swamp Rose

what wetness? lots of rain? heavy or compected soil, poor drainage. How are they declining? There could be lots of reasons why the roses are not doing as well anymore and just about all of them can be fairly easily rectified.

Thanks for all your comments. I'm sorry I wasn't clear.

My trellis that I use to support my climbing roses is near the back of my lot, near but not in the part that has standing water when it rains. The soil dries out in the summer and fall, and hasn't been that wet this year due to a dry spring, but is usually quite wet in the spring. The soil is clay, but we have amended it on each side of the trellis 2 feet wide and 18 inches deep around each rose.

After a couple of years, the roses don't thrive, they seem to get smaller and weaker, even though they get the same fertilizer schedule as the rest of my roses, and don't appear to be as affected by black spot or insects as the rest of my roses, since I stopped using chemical sprays. They have fewer branches, less foliage, canes are thinner, fewer flowers, but no visible sign of disease. The roses are Scent from Above and Fourth of July.

The thing that makes me think it is the damp ground is that the two in the back of the trellis, nearer to the area that gets a bit swampy in the rain, are not doing well at all, and I'm not sure they'll survive another winter.

So I'm thinking of moving the Scent from Above's so I don't lose them, and was hoping to replace them with climbers that deal with the damp a bit better. If not, I could try the planters, but I'm not sure how having the roots above ground would work with our zone 5 winters.

I'm not sure what French Drains are, but I'll look that up. The water issue is caused by the fact that all the water from multiple yards all drain to a storm sewer not far from the trellis (in another neighbors yard). So I'm not really in control rerouting all the water sources, I'm hoping that the research on French Drains will give me some ideas on what we can do.

I'll look up rosa palustris.

Thanks for all your ideas and any new ideas you may have!