Maple Tree · Gardenality Genius · Zone 10A · 30° to 35° F
Hi Barbara-If the leaves were turning yellow, orange, or red in the fall or early winter this would most likely be normal as most evergreen azaleas have to shed the older leaves which will turn these colors before dropping. As the weather gets cooler leaf color changes are normal. Leaves turning yellow then possibly orange or red during the summer usually indicates some type of stress. Too hot a temperatures, too much hot direct sunlight, too little or too much water, or nutrient deficiencies can cause this color change. Are all the healthy and struggling azaleas planted in the same location and type of soil? Are they all newly planted? If they are I would assume nutrient deficiency may not be the problem at this time as some are doing well. Are the older larger leaves discoloring more so than the newer foliage? Too much water or too little can stress a new plants more easily many times causing the leaves to turn yellow first than possibly changing to orange then or to red before dropping. Too little water especially in heavy clay soils can cause root rot. High soil moisture and warm soil temperatures help to develop this root rot. Eventhough you have ammended the soil around the plants some holes may be acting as bowels to hold in too much water around the roots zone. Over watering or rain fall may be affecting some of these plants causing stunted growth and discoloring of the leaves.
I would first check the soil around the unhealthy plants for too little or too wet a soil. When digging down 6 inches or so the soil should feel cool and moist but not too wet or dry. If you could let us know what you find and answer these few questions it hopefully will help to find the problem. If you could also upload a picture of an unhealthy looking plant and an upclose picture of the discolored leaves it may help to identify the problem. Above this comment and to the right of your name below your question you will see where you can upload your pictures.