What did I do wrong with my roses?

When my Grandmother died I wanted to take her rose bushes with me when I moved (I was living with her to help her) I was afraid being transplanted would kill them so I took some starts.

I did all the things my Grandma had taught me to do. I cut a piece longer than 6 inches, put root start on them and put them in a pot of potting soil, watered them well, and covered them with a jar.

After a month I checked them and they had leaves growing (which is more than I had ever managed before) I uncovered one and the next day the leaves were shriveled, so I left the others covered. But after another few weeks they had all shriveled too.

Luckily the original bushes are doing pretty good, but I would like to know what I did wrong to I'll know for next time.