Answer: Rhododendrons need soil that is evenly moist yet well drained, meaning it should be damp like a wrung out sponge and never sopping wet or bone dry. Planting sites in morning sun or bright dappled light all day help with heat stress, and using a flat layer of organic mulch about two to three inches deep over the root zone helps with moisture retention and also helps keep the soil cool.
Yellowing lower leaves often indicates overwatering. To know if you need to water, dig into the soil with your finger. If it is still damp, do not water yet. When you do water, water thoroughly so it soaks down into the top eight inches or so of soil and encourages deeper rooting to where the soil naturally stays moister longer. After watering wait a few hours and then dig down to see how far the water soaked in; sometimes it can be surprising. It is better to water deeply less often than to sprinkle lightly every day. Also, when you water, try not to get the leaves wet. It is more efficient to use a soaker or drip system applying water only at the soil level. This method also keeps the foliage dry and thus reduces the opportunities for foliar disease problems.
Since this is a new plant I would also suggest you consult with your nursery and/or county extension. Good luck with your plant.
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