Diseased arborvitae?

Question: These three arborvitae (?) have been planted in front of my house for about 10 years. Now they look like they are diseased with brown spots. About a year ago, I planted a small arborvitae on the other side of the house, and that started to brown in the same way and is now completely dead. Is there any way to save my large shrubs? Thank you!

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied October 28, 2024, 11:30 AM EDT
response: The foliage yellowing, browning, and shedding on the interior / older part of the branches is normal for this and many other kinds of evergreens. (Some shed in fall, others in spring.) The first plant pictured looks like a Hinoki Cypress (botanical name Chamaecyparis obtusa), not arborvitae, though the second plant does look like a dwarf variety of arborvitae. Both plants prefer a full sun to mostly-sunny exposure, with 6-8 or more hours of direct summer sun, to thrive and keep their foliage dense. That said, there are hundreds of varieties of Hinoki Cypress, and not all grow as densely as others by nature. On dense plants, the seasonal loss of the oldest foliage isn't always very noticeable, but on more open-branched plants as this, it can be quite prominent. There isn't an easy way to regain the density the plant might have had in its youth, if that's what you want (no harm to the plant to have it growing as-is if you like the look).  Although not as much of a concern in a drought year like this one (which likely stressed even well-established plants, unless they were being watered occasionally), if the downspout nearby empties into the plant's root zone, that could cause root damage or death during wet periods. Hinokis, arborvitaes, and many other evergreens do not handle poor drainage or excessive soil moisture well, though neither are they particularly drought-tolerant. It's hard to say when each plant became stressed (more so for the now-dead arborvitae), but that might have been a contributing factor, along with light levels if they are in a more shaded exposure.  If you want to replant the arborvitae, you can do so now or wait until spring. Either way, be sure to loosen well any tangled/matted roots that might be making it root-bound when removed from the pot. Not loosening roots can make establishment harder for the plant and can be one reason why young plantings (those in the ground less than a year or two) can fail, in addition to how they were being watered. If deer visit the yard, you might want to choose a different evergreen or just watch for indications of browsing damage, as they do enjoy eating Eastern Arborvitae (Thuja occidentalis). Interestingly, they seem to usually avoid Western Arborvitae (Thuja plicata and its hybrids), though not as many compact, dwarf selections of that species exist as do for the Eastern. If useful, one option for a part-shade-tolerant and more moisture-tolerant needled evergreen that deer avoid is Japanese Plum Yew (Cephalotaxus harringtonia).  Miri

responder: The Question Asker Replied October 28, 2024, 6:28 PM EDT
response: Thank you so much for the incredibly detailed answer. Very helpful! Thank you again!!  Paula

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied October 29, 2024, 9:02 AM EDT
response: You're welcome!