SoFl , I think we had a post on this last year I found a great vintage one at the restore but have yet to use it. I think Cori Ann might have gotten one to use with her trees or something. I'll try to find the post because there were some positive things said about them.

Most feeder roots are in a mat just below the soil surface. And not in pockets deep down, in exactly the same spots as where a root feeder happens to be inserted each time.

LOL!! I was gong to make a similar comment....just where do they think this root system is?? By the look of the length of that rod, I'm guessing somewhere close to the center of the earth, rather than concentrated just below the soil surface.

It worked beautifully on my old, giant live oak trees in Austin, TX, the only problem was that it took a whole day just to do one tree. I don't know about roses.

It works great in thick clay soil that water doesn’t penetrate. The metal spike penetrates the heavy clay soil that water just wouldn’t be able to on its own. Using the metal spike alone is a bit like aerating. It gives water (and fertilizer if you add it), straight to the roots in my situation. In the sandy soil of Florida, I’m not sure it would benefit.

The long, thicker roots on a rose bush do some work but are mainly to stabilize. It is the thin, tiny white roots that do all the work. Probably female ones!! The fertilizer plus water, should be able to get to them through your soil. If you have planted a rose for instance next a tree, then a 3 foot piece of 2 inch diameter plastic piping works very well. You just leave a small piece showing and stick the hose down it.