Agave plants generally do not require much fertilization and can actually be damaged by over-fertilization. However, if you want to give your Agave a boost, you can use a slow-release, low-nitrogen fertilizer once a year in the spring. Avoid high-nitrogen fertilizers as they can stimulate excessive leaf growth and weaken the plant. Additionally, it is important to make sure that the soil is well-draining, as Agave plants are susceptible to root rot if the soil is too wet.