Never have used it but its nutritional composition is somewhere about 6-1-1 or so in nitrogen, phosphorus, and potash. I typically like to use something that is higher in phosphorus since it stimulates root grow and ultimately flower production. The only other downside is that it can acidify the soil so if your soil is already acidic, you could be lowering the soil pH even more.

I agree with Miguel - it wouldn't be my first choice for clematis. But then I have naturally acidic soils :-) If you wish to follow an organic regime, I'd suggest alfalfa meal (2-1-2) as it tends to be a bit more balanced nutrient-wise and with a lower nitrogen concentration. Or, if you can easily find them, a complete organic rose or vegetable fertilizer would work equally as well. I use Dr. Earth myself (when I don't rely just on my bunny and his 'produce') but Espoma also makes a similar organic product. And there are others.

Thanks..i wasnt sure... its good on my Blueberries and azaleas, but they like it acidic anyway