I use alfalfa and rose fertilizer on mine and they seem to like it. I do the roses and clematis the same way at the same time.

Harry..I totally concur with Bob..each Spring all my flowers get a topdressing of composted cowmanure and Alfalfa Tea....and of course my clems and roses get rose fertilizer!!....My clematis and Roses LOVE it..and they show me by growing and blooming like mad...Jeanne

I put some of my rose fertilizer (Bayer all in one) on my new clematisis and they are growing like crazy.

That is exactly the fertilzing regime I use, although my rose fertilizer is another organic - Dr. Earth - and the alfalfa has been has been routed through my bunnies first :-)

Just an FYI, but the Bayer product is NOT organic and contains systemic pesticides.

I just put Rose Tone and composted manure on my roses and any clems not already budded/blooming yesterday.

Tomato food isn't high acid. Use it. One might want to avoid Rhododendron/azalea food which is high acid.