Question: My gardenia plants are yellow. Someone told me that was iron deficiency. What should I add?
Answer: Gardenias are very prone to iron chlorosis, and yet we continue to grow them along and west of I35, the general line of shift from acidic East Texas soils to the alkaline soils of West Texas. Recognize iron deficiency in gardenias by yellowed leaves with dark green veins, most prominently on the newest growth first. In fact, the yellowing can become so severe in Austin, San Antonio and westward into Kerrville and Uvalde that the plants will turn pure white, with no chlorophyll at all left in their leaves. You can add an iron/sulfur material to supply the needed iron and to keep it relatively “available ” by acidifying the soil, but you also need to start out with a planting mix that is all organic matter, including peat moss and bark mulch. Truth is, you probably should grow your gardenia in a container in those areas with extremely alkaline soils. If you do opt for the container route, remember to set it in the garage any time the temperature will drop into the low 20s.