The kind of substrate where agaves grow in habitat is generally of a very poor quality, and they have evolved to be efficient at extracting nutrients from it. When grown in containers with a confined root run they are dependant on us to provide for their needs.
Some of the larger agaves can be quite hungry during the growing season and will benefit from regular feeding. Recently repotted plants should have everything they need for the first 6 months and then if they are kept in the same pot for a second season they should be given a balanced feed at least every other watering. Plants that remain in the same pot can be top dressed with fresh soil containing a slow release fertiliser as an alternative to applying liquid feed. Do not feed Agaves from September onwards as this can cause soft growth which can be fatal during winter.
By far the easiest feed to apply is a liquid feed added to water. Alternatives are proprietary cactus fertilisers that are dissolved in water. The latter also contain essential trace elements.
Much of the advice available for feeding of agaves seems to be grouped with care of cacti where a high potash fertiliser is used to promote flowering. I prefer to give agaves a balanced feed at least once a month.
The plenty of advice around that recommends using a diluted feed. This should really depend on how dry the compost is to begin with. Imagine if a pot full of moist compost that is given a liquid feed, this will be diluted to some extent by the moisture already in the soil. If we were to give the same feed to a plant in completely dry soil then the roots would be exposed to a strong fertiliser solution and could suffer damage through burning. Also by giving half or quarter strength feed we are depriving the plant of nutrients and would need to give diluted feed more often.
It is far simpler just to follow the instructions supplied with the fertiliser.
So should we let the soil dry out between watering ?
This is probably just another myth that has come from cacti growers. The important point is not to over water or let the soil become water logged. The best approach is to understand how a particular plant grown in its natural habitat and the rainfall pattern and dry periods it experiences.
On the next page we take a look at Watering.