Cacti and succulents have relatively low nutrient requirements. Cacti need fertilizer only once or twice a year during the late spring or summer when they are actively growing. Use a houseplant food that is higher in phosphorus than nitrogen, diluted to half the recommended rate. Other succulents may be fertilized in the same manner three or four times during the brighter months.
Types of fertilizers
Fertilizers contain the nutrients your plants require for healthy growth. Fertilizers are either organic or inorganic, and available in a powder, granular, liquid or solid form. The advantage of inorganic fertilizers is that their chemical content is consistent. Organic fertilizers are high in trace elements yet they may lack some elements which will cause a deficiency with prolongued use.
Main elements and their function in the plants:
(N) nitrogen - encourages good top growth, it helps to build protoplasm, protein and other components of plant cells.
(P) phosphorus (phosphate) - encourages good root growth. Aids in the ripening of fruit and seed germination (seed viability).
(K) potassium (potash) - encourages good flowers and fruit.
You can use a low nitrogen slow release fertilizer in the early spring. A 5-10-5 (NPK) compound works best. Mix it in with the soil and it will feed the cacti all summer. Another method is to use a water-soluble cactus fertilizer. Some people use brand called "Cactus Juice", and it is mixed 1/2 tablespoon per gallon of water. Schultz and other manufacturers also make liquid fertilizer. With this method you fertilize every two weeks during the growing season. You may find this works better for desert cacti than using a granular mixture. Both methods are good, but cacti seem to respond better to liquid fertilizer.
In the dormant period (November throughout March), do not fertilize at all.