Answer: There are several possible caused for why this might happen. If these are new plants, and the drying begins at the tips of the branches, they may actually need more water. A light sprinkling will not be sufficient if the weather has been dry. When you water, water slowly and thoroughly so it soaks down deep and encourages deep rooting. After watering, wait a few hours and then dig down and see how far the water went; it can be surprising. To know if you need to water, dig into the soil with your finger. If it is still damp, don't water yet. There is no set schedule for how often to water as it depends on the soil and the weather. Once established these should not need any watering except possibly in a case of true drought conditions.
New plants should also be mulched with several inches of organic mulch and that depth should be maintained year round by fluffing it with a rake and adding more as needed. This will help maintain a more steady soil moisture level.
Overfertilizing can also cause browning. These shrubs should not need much if any fertilizer. An annual topdressing of compost and the regular mulch layer should be sufficient, although you could also apply a light amount of all purpose granular or slow release fertilizer such as 10-10-10 each spring per the label directions.
There are also some possible pest and disease problems that might cause discoloration. If the above does not sound plausible, you might want to consult with your local professionally trained nursery staff and/or county extension to try to obtain a specific diagnosis of the problem. They may appreciate a photo of the overall plant and closeups of the discoloration along with a freshly cut sample kept cool and enclosed in a plastic bag. If it is something that requires a chemical control, your county extension will have the most up to date information on what to use and how/when is best to apply it.
I hope this helps you trouble shoot.
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