Most native and desert-adapted plants in the landscape do not generally require fertilizer as they are adapted to our soil conditions. In most cases, fertilizers are generally applied to prevent deficiencies. If fertilizers are needed, one application for the year is usually sufficient. If you did not fertilize in March or in April, go ahead and fertilize your landscape plants if necessary. However, it is recommended to fertilize your landscape plants the early part of May. For more information on fertilizing and plant deficiencies go to the University of Arizona Cooperative Extension Publications: http://ag.arizona.edu/pubs/garden/az1020.pdf
Periodically fertilizing may be needed for plants in containers as nutrients in the soil will have diminished over time. Always follow directions on the label.
Continue to fertilize your warm-season annuals and herbaceous and woody perennials in containers if necessary.
Cacti and warm-season succulents in containers should be fertilized at least once during the month. Do not fertilize any winter-growing succulents such as Live Forever (Dudleya saxosa ssp. collomiae), Succulent Geraniums (Pelargonium spp.), Iceplants (Malephora spp.,Drosanthemum spp., Cephalophyllum spp.), Living Stones (Lithops spp.) and crassulaceous plants (Kalanchoe spp., Cotyledon spp., Echeveriaspp.) as they are now undergoing their summer dormant period.
Continue to fertilize your vegetable and herb garden as needed.