Roses should be fertilized with a granular fertilizer every four to six weeks during the growing season, suggests Heirloom Roses, a supplier. The first application of fertilizer should go on when the plant ceases to be dormant, shows new growth and produces at least five leaves.
The last application of fertilizer should go on about eight weeks prior to the anticipated date of the first frost in cold climates. This allows the roses to harden off and avoid damage. A granular fertilizer works slowly over several weeks, but a liquid fertilizer is appropriate for roses that show signs of distress, Heirloom Roses notes.