Ferilizing Photinia, Iris, Hollies and Italian Cypress

Q. I want to know when and how to fertilize most of my shrubs.  I have a lot of Photinia, iris, Japanese hollies and Italian cypresses.

Iron chlorosis on photinia in rock mulch

A. Flowering plants should be fertilized a few weeks just prior to flowering and the development of new growth. If flowering and new growth coincide with each other, then one application of fertilizer just prior to that combined event is all that is necessary.

            If new growth starts and then flowering occurs later, then you should probably fertilize a second or even third time during, or slightly after, flowering. Usually if we grow plants specifically for their flowers (roses are a good example) then regular applications of fertilizer through their flowering season might be considered. A slow release fertilizer could be substituted for multiple fertilizer applications.

            Once they stop growing in late summer and fall, they send food reserves into storage. So they should have nutrients available to them during fall as well. We sometimes call this late fall fertilization. This can be advantageous for woody trees, shrubs and even lawns.

            Generally speaking we can fertilize most plants once in the spring, now, and be done with it for the remainder of the year. Flowering plants that we appreciate for their flowers need to be fertilized a bit more often; once prior to new growth and then again after blooming to help build up reserves. So your iris probably fit into the second category. The others, into the first category.

Apply the fertilizer close to the source of water that is irrigating the plants and let the irrigations take the fertilizer into the root zone.