Although cacti are are native to semi-arid or desert areas, they can benefit from fertilization. A number of commercial cactus fertilizers are available. Cactus fertilizer differs from other fertilizers in that it is much more diluted. Understanding that, making your own organic cactus fertilizer is very easy.
Read the recommended mixing instructions for your organic fish and kelp emulsions.
Add 1/8 of the recommended fish emulsion base to the recommended quantity of water. For example, if your emulsion recommends 1 tbsp. of fish emulsion per gallon of water, mix 1/8 tbsp. of fish emulsion in with 1 gallon of water.
Add 1/8 of the recommended kelp emulsion base to your water. Kelp emulsion has a number of trace minerals that are generally beneficial to plants, including cactus. By mixing 1/8 of the recommended amount of both fish and kelp emulsion, you are making about a 1/4 strength cactus fertilizer.
Close your container. Shake the container vigorously to start mixing the components.
Allow the container to sit for two to three hours to ensure that the fish and kelp emulsions are properly mixed.
Water your cactus with this low-intensity fertilizer in place of its normal waterings.