I have alkaline soil also and I have been told not to do multiflora grafts. Dr. Huey does the best in my area. Maybe someone with more experience will tell you to add sulfur or something to lower your pH. I am still a newbie.

Since roses are expensive, I'd get a soil test through the county ag extension and follow their recommendation for amending with sulfur. You'll learn other useful things about your rose soil. Sometimes excessive levels of phosphorus contribute to chlorosis problems.

Then after taking the soil sample, I'd start applying iron. It sounds like your multiflora plants are hurting, and their winter hardiness could be affected. A remedy that some here have found effective is 2 oz iron sulfate (copperas) mixed with a gallon of well-moistened compost (or peat if you have no compost) applied under the mulch to each plant. Or you can use a chelated iron product regularly. Be sure you maintain a good organic mulch, which promotes nutrient availability. I don't have experience with high alkalinity, but I would try to save the mf plants if I liked the varieties. As roseleaf suggests, you might do better to prefer ownroots and Dr. Huey plants in the future. But I know some here do grow mf plants in moderately alkaline soil.

Or, you could use elemental sulfur sprinkled around the multiflora bushes.

Here is a link that might be useful: lowering pH with sulfur

Thanks!

I have moderately alkaline soil, and just add chelated iron to my fertilization schedule. Most of my grafted plants are on multiflora, and do fine that way. I actually prefer multiflora to DR. Huey here. But as Michaelg said, get a soil test before you do anything.

My initial reaction is to ask how long those multiflora grafts have been in your garden. If this is their first year (& especially if they were planted late), I would withhold all the soil amendments for the time being, give them some extra winter protection this year & see how they perform next season. Obviously, your growing conditions and mine are very different, but I don't expect my multiflora grafts to perform really well until their 2nd or 3rd yr.