I recently planted out Purple Eden (Ebb Tide)-used mycorrizal fungi,just to see if they make any difference. But only now (reading a comment of Seil's on another thread) does it occur to me that I do have some gel rooting hormone,and that this might be of some help to give this particular rose (not famous for it's vigour) an extra boost. Thoughts?

Hello,

Rooting gels are usually a synthetic form of auxins, specifically indole-3-butyric acid (IBA), designed to initiate root production where these is none (on a cane of a cutting, etc). If you want to increase the vigor of your rose your best bet is a balanced fertilizer with a slighly higher middle number (the phosphate number); don't get carried away. Any in balance in your soil chemistry will shift your soil's pH and interfere with nutrient uptake.

Please note that I said to be VERY careful not to use much rooting hormone or it could be detrimental. The OP was concerned about fall planting in a cold climate and wanted to know if fertilizing would help the plant root better before winter. In my opinion, no, it will not and they would do better to use some rooting hormone than to fertilize. Fertilizer is more likely to produce top growth that will not have time to harden off before winter and will die.

Thank you both for your replies. Please bear with me as I explain this particular situation.
I got this Purple Eden (Ebb Tide) plant at a local garden center; it came from Rose Barni,the famous nursery nearby in Pistoia. I bought it because, amongst the other PEdens (all from Barni),this one looked remarkably more vigorous. Now, Barni does this thing: their potted roses are planted with the graft very much above soil level; this way they can get away with selling them in rather small pots. I myself feel very strongly that the graft should be AT SOIL LEVEL or slightly below,but it makes perfect sense that a nursery would sell potted roses this way for practical reasons. So I re-potted the plant into a pot that was large enough to contain the root system with the graft almost at soil level.
But I made a mistake. I had a plant of Huddersfield Choral Society,and a large-ish cane broke off last spring, so I stuck it into the pot with P Eden, just in case it decided to root. OMG, did it ever. At first it seemed small and harmless,but then quite suddenly it took off like a maniac! It became clear that the new rose was totally bullying P Eden,but by this time the weather was very hot and dry, and I was afraid of trying to seperate the two roses in such conditions-I risked losing both of them. So, once September rolled around-it was still hot, at the time, but the sun is by now much lower and the days much shorter- I decided to seperate them. HCS had a booming, bouncing-good root system, but poor P Eden hadn't been able to do very much. Still, I decided to plant them both out. I felt that since I'd already shocked poor PEden by seperating it's roots from HCS,I might as well try just planting it out, rather than re-potting it again. This might have been a mistake.
The fact is that I'm afraid that PEden's roots might not be able to take up fertilizer yet,which is why I was wondering about using a touch of the hormone; I do want it to "root better",as Seil put it. If I did, how could I apply it? Dig down to the roots and put a drop onto an exposed root? Obviously it would've been better to do this at planting time,but I didn't think of it.

Do u have access to any form of alfalfa, hay, pellets or meal? That can help with root growth.

I put alfalfa hay in when I planted it,Vaporvac. That stuff is great!