Roses should be fertilized for the first time in spring, after pruning. Preferably use organic fertilizers, such as dried cow dung. This contains all the necessary minerals and trace elements for a healthy rose. Organic fertilizer makes the soil more airy and helps it to retain moisture more easily. Apply the fertilizer and lightly work it into the soil to prevent fertilizer burn. If your soil has a low pH level (acidic soil), it is best to mix a calcareous fertilizer into the top layer once a year. After the first flowers in July some extra fertilization is advisable, possibly with some special rose fertilizer. This fertilizer is rich in potassium for a more intense flower colour and stronger plants. The extra magnesium turns the leaves of the plant deep green. Do not use any more fertilizer after August in order to allow the rose bush to harden off for the winter. Potted roses on the patio must be fertilized regularly as the pot offers only limited buffering.
If your potted plant is withering, provide new, fresh soil and add some (preferably organic) rose fertilizer from the garden centre.