Hmmmm. Bart, as we've discussed before, paulownia form deep tap roots. But I'm not sure how wide-spreading their feeder roots are. The general practice (except for me and my ramblers! lol) is to not plant roses under the canopy of a tree. But paulownias tend to have a high canopy as they mature, and grass doesn't have a problem under my neighbor's tree. So if the roses are already established they should be able to compete with the tree's roots. If you're planting new roses near the tree, I'd keep them at least 10 feet from the trunk. Since the tree is young itself, the roses should get a foothold before the tree roots reach their space. Hopefully the roses will benefit from the shade, without undo root competition.

I can't make a recommendation for planting roses near your other trees. It will depend on the species, the size/age of both the tree and the rose, etc.

EDIT: just as a warning, I wouldn't plant anything delicate or small directly under the paulownia. They are known as messy trees, and their large leaves could easily smother a small plant in the Fall, not to mention the flowers and seed pods can cover the ground.

The feeder roots are, I think, the real problem. Well established at my house, a cedar tree (Juniperus virginiana however it's spelled) was at the top of our hill,, Lousy soil a heavy red clay developed on Knox chert and dolomite. It didn't grow, but it didn't die and had been there for (according to neighbors) at least thirty years. To the south, slightly down hill and for about 100 feet are where I had my first rose beds. (Only later did I learn that was where the former owners had their tobacco field which probably explains why some of my roses had horrific root gall problems in one specific area.) Anyway, We emended soil put in irrigation and planted what was supposed to be an homage to Souv. de Malmaison bed. They grew but didn't thrive anywhere nearly as well as the roses farther down hill. I went to transplant two lesser performers, and I encountered ROOTS! Lot's more roots than the roses could have made (and kept their above ground selves so sparse.) I snipped off a root and all of a sudden, the scent of cut cedar hit me. Those roots hadn't expanded when we built the bed, but opportunistic sob that it was, we offeree bothe water and better soil, and the tree did what came naturally.

That rose bed is gone and the tree is bigger and we are having to cut off lower limbs so we can mow under it and over where the rose bed used to be.

Generally, plants' feeder roots extend out past the circumference of their canopies to make use of the water falling from their "drip zones". Much of the water which falls ON a plant, runs OFF it to the edges of its growth, the drip zone, and soaks into the ground there. That's where most plants (including roses) concentrate their feeder roots to absorb as much of that moisture and the associated dissolved nutrients as possible. That drip zone is also where the majority of the tree roots concentrate, not to mention the horizontal stabilizer roots which assist them in resisting strong winds. If your tree can realistically be expected to produce a sizeable canopy within the time you expect to still be gardening there, keep that in mind and plan accordingly. Also remember the roots ARE water seeking. They WILL find your irrigation faster than you imagine and they WILL infiltrate your planting holes, making perfect use of the amendments, fertilizers and irrigation much faster and more efficiently than any of the roses can. I'm regularly surprised with how far tree roots travel from yard to yard when seeing how they pull up neighboring yards when strong winds after heavy rains topple them. Good luck!

Bart, It depends on the tree, the conditions, and the plants you're asking to compete...and your willingness to babysit and coddle. My garden is mostly wooded, so I grow many (too many!) plants under trees. My front yard is really the only full sun area I have, and where most of my roses live. Otherwise, I garden under trees.

Planting the roses, perennials and trees at the same time, and same relative ages, at reasonable distances, will allow the roses to become established *before* the tree roots can reach their growing zone. Tree roots by nature *are* invasive. I realize that my water conditions are not nearly as dire as yours, and my plant palette is different, but I can (and do) successfully grow multiple plants, including ramblers/climbers, under various species of trees. Hostas, ferns, cyclamen, heuchera, aruncus, other shade lovers, and of course Spring ephemerals (which die down in summer) all thrive under my oaks. But I'd never dream of trying the same plants under, for instance, a shallow rooted maple. There, the only safe bets are the also-invasive ground covers (vinca, English ivy, bishop's weed), which I'm still trying to eliminate from places they grew into from where I first planted them under the maples, lol. Of course your conditions are totally different from mine, Bart. But even so, there should be perennials and drought resistant shrubs (natives?) that will do well within the dripline of deep-rooted trees. Just avoid shallow rooted trees, if you can. By the way, fig trees are among the worst for invasive roots! They WILL find water at any distance.

Thanks all! I think it will be worth a try. My idea is to site a Paulownia right in the path of the south-western sun,so it will cast it's shade on the roses in the later afternoon,so no roses would actually be under it. I already have one growing nearer to the roses (the one I moved last fall) ,but again none are under it.. Those closest to it are all climbers. Actually I think that this one is more likely to cause problems for the roses than the new one I'm planning, but maybe it won't. On Internet I'm seeing rather contradictory info about the root system of Paulownias; I DO know that when I moved this one, I found no deep-growing tap root; I honestly think that the tap root just branched out horizontally instead of going down! but I have no idea what it might do in this new spot. Another factor is the sharp slope of my land-the tree is growing below (lower down on the slope) the roses. I don't know how that will influence root competition either, but it's ddefinitely different fron growing stuff on a flat site. I do know for sure that the sun will harm the roses a heck of a lot more and faster than tree root competition can do!