What to buy---own root or grafted---it depends. In my Z4 area, hardy shrub roses do best on their own roots. If you have alkaline soils, roses grafted on Dr. Huey may do better for you. If you have acid soil, roses grafted on R. multiflora may do better for you. If you live in sandy Gulf Coast soil, rose grafted on R. fortuniana may be required to resist soil nematod damage. Some roses are not vigorous growers on their own roots so must be grafted on a vigorous root stock to get them to grow decent. The best advice I can give you is, seek out a Rose Society in your area & see what the people in your part of the country are doing with their roses.

Grafted means the bottom part of the rose (roots) is 1 variety and the top part (stems or canes) is a different variety. They are joined together by a knobby structure called a 'bud union'. The top part produces the desirable flowers and growth habit "as advertised".

Own Root means the bottom part and the top part of the rose are all the same rose.

Grafted roses can produce "suckers". Suckers are canes or stems from the roots. They do not have the same flowers or growth habit, and are not usually considered to be very desirable.

Grafted problems:

1. The suckers can sap the strength of the desirable variety, even kill it, if you allow suckers to take over, and you are left with what the roots produce (less desirable).
2. The "bud union" can get woody and worn out and the rose can lose vigor.
3. In climates where freezes and snow occur, the desirable variety can be killed and you are left with what the roots produce.

Own root roses seem to do very well in Southern California.

I'd recommend getting rose varieties that are well-adapted to your area/climate/soil, and let them grow on their own roots like the other plants in your garden.

Randy

Grafted gives more "instant success" with larger plant size and blooms early on. One thing I never realized was to get a root stock compatible with your soil. So Dr Huey is great for alkaline soils, multiflora for acidic, fortuniana for hot & sandy, to name the most popular. It can be hard to figure this out just by looking at a plant in the store, but forum members seem to know who produces roses on which rootstock. Most of the specialty, smaller nurseries are on own root production from cuttings.

I think the first response above summed up the basics nicely. Interestingly, it seems in general that own-root roses handle a wide variety of soil conditions. Really I prefer own-root, despite the extra initial time required for the plant to mature. Still, its fun watching the little plants take off. I tend to think --buy own-root if possible, unless there is a specific reason not to. For example, if a variety is known to be weak-growing on its own roots, which you can find out by asking on this forum. Most modern roses of the past couple decades do just fine on their own. Many from mid-20th century also do, though quite a few of those will never get as big on their own. Some are just plain disappointing on their own.

Some folks in very cold areas swear that a grafted rose is the only way to go because of the bigger plant produced in that critical first season when it's building strength to withstand the onslaught of winter. However, they also make sure to plant the bud union deep and expect eventually the grafted variety to develop its own roots in addition to the rootstock underneath. In Southern California you should never have to worry about cold-hardiness. If you go with grafted, then Dr. Huey or fortuniana should be your choices where you live. Dr. Huey is really the standard for the California-based rose industry, but fortuniana has advantages too, including a bigger plant with more and bigger blooms by the third and fourth years. The easiest choice for me is if I can only find a rose on one rootstock, I buy it that way. Then if I don't like how it grows after a couple years, I just root it on its own roots. Of course we really should reserve that practice for roses at least 20 years old, due to patent concerns. And that approach requires patience, but if growing roses were just about instant results, we might as well just go to the florist each week. ;)