Cacti are not heavy feeders so a slow release plant food like Osmocote plus used at one half the recommended strength is a great choice for both potted cacti and those growing in the ground. There is also an Osmocote made especially for cacti (Osmocote Cacti and Succulent) and a potting mix made especially for cacti that contains Osmocote. Just remember that cacti do not like to be overwatered or over fertilized. An application of Osmocote once a year will keep your cacti well fed. Keep growing, Marianne Binetti