My cousin Joyce, who has the greenest thumb of anyone I know, told me her favorite rose fertilizers are : water with any/all of the following added: fish emulsion, seaweed,molasses, apple cider vinegar.
Yeah,I know, this sounds like a Jerry Baker recipe. But I trust my cousin. (And at least she doesn't wizz in her garden.)
My own mix of organic fertilizer has a dz. different ingredients.
Eg. : Fish meal, bone meal, kelp meal, cottonseed meal, blood meal, flaxseed meal and more. I mix it together with a local rose friend. It is very expensive and will cost you 2 to 3 dollars a lb. so we only use it for potted roses.
I was using the usual chemical fertlizers for my roses and nothing had ever done well until I finally discovered a rather inexpensive premixed natural fertlizer at a local nursery and BANG... The blackspot almost completely fanished, the bushes grew beautifully and the blooms were manaficient.
Charliebear, you didn't say what the natural fertilizer is!!
I like alfalfa pellets, yep the kind you feed rabbits or horses. Sometimes I just scratch a cupful into the soil, other times I make tea--along with seaweed, molasses, etc.
I used a product called Dynamic Lifter in Australia. It's made out of chicken poos, not very expensive. The result is great. Roses get extra performance out of this stuff. Chicken poo is much richer in nitrogen than other stuff because chicken are force-fed with food made out of animal sources. That's why chicken poo is generally too hot for plants. But once composted and treated in a factory, it's very good for plants that need nitrogen like roses. I find this stuff helps roses to have bigger blooms and more new basals.
So I think you might like to try products made out of chicken poos. the smell is bad though! The only way to use it is to take the mulch off, put it in and put thick mulch on top. Finer grain type of mulch shuts the smell out better. It can also be soak in water over 1-2 days to become a quick soluble fertiliser to water the roses every 2 weeks. But the best application is late Winter to prepare for Spring growth.