What is the best fertilizer for roses?

Depends on which plants you are wanting to feed. Indoor (or containerised) plants really need a liquid food to reduce build-up of salts. You should be able to find most of these at your local plant nursery. They include the three essential nutrients - Nitrogen (N) Phosphorus (P) and Potassium (K).

Plants in your garden generally need a fertiliser which is high in N and K. There are many different forms of these - but it is often best to use a "slow-release" (SR) fertiliser. The component which is released slowly is the nitrogen component (which can "burn" the roots if released too rapidly).