Hi Judith :-)
If you want a natural or organic alternative to superphosphate you can also use bonemeal. I have not used bonemeal in years. Now my roses get mostly phosphorus from cowmanure compost and liquid organic fertilizers. I cannot see any difference in my roses. I really like some of the liquid organic fertilizers with seaweed and lots of other ingredients.

If your soil contains very little phosphorus naturally it can be good to mix in bonemeal when the rose is planted. It lasts a long time so it is not used every year.

Superphosphate, simply, is rock phosphate that has been washed in an acid bath to make the phosphorus more readily available. Superphosphate can easily burn the roots of plants and is not recomended to day for use in established gardens, by knowledgeable people.
Colloidal phosphate is a rock phosphate from a different mine.

Rock phosphate and colloidal phosphate are both pulverized forms of the mineral apatite, generally by-products of a mining process, and slow-release forms of phosphorous. "Colloidal" simply refers to the particle size.

Superphosphate is apatite that has been reacted with an acid, thereby changing the chemistry and concentrating the phosphorous. As a man-made chemical fertilizer, it is not acceptable in a certifiable organic garden.

Also, if you look at the ingredients on superphosphate, there is a fairly high chlorine content. It's a residue from the acid wash. It will kill your lovely earthworms.

jill

Manure, compost, cottonseed meal, fish products, mixed organic fertilizers, and sludge all contain phosphorus, so there is probably going to be plenty of it in your soil. You might find rock phosphate in big bags at a feed store, but I am not sure it is worth the trouble. Generally garden soils that have been fertilized for a while, whether organically or inorganically, have a big surplus of phosphate.