Hi Sue and thanks for your question and great pictures of your poor boxwood plants. It looks very much like phytophthora root and crown rot, a fungus-like organism that lives in the soil. When it kills the root area, part of the top or side of the plant dies.

This is often a drainage problem but can also be related to soil pH and heat stress. There is one chemical available for home use,
Monterey Garden Phos at 2 to 4 teaspoons/gal water as a foliar spray. This will not solve the problem, as once the spray is done acting, the disease will return since the plant is already infected. It is more of a preventative.

https://pnwhandbooks.org/plantdisease/host-disease/boxwood-buxus-spp-phytophthora-root-crown-rot

I'm sorry this is not better news but it seems like an opportunity to try something new as a border.

Thank you!

Hi again Sue and thanks for your great question about disposing of diseased plants! Please don't put them in the compost bin. This only spreads the problem, as the spores are water soluble and have to be heated to 140 degrees Fahrenheit to be killed. So there seem to be two options: burn them or put them in the trash.

If you have a place to burn them, this would be easiest, just keep them away from other plants and off the soil while you let them dry out. Since most of us don't have this option available, I would maybe feed them into the trash one at a time, cutting small pieces so you can fit more in each week/month.

There is also something called "boxwood decline" which also fits your plants but is more of a mystery. I'll include the website but I think the process is still the same as it will eventually kill the plants and its cause is unknown.
https://www.newgenboxwood.com/whats-wrong-with-my-boxwood#decline

Thanks for not just dumping them in the compost and for your concern about not passing on this problem to others!

Thank you!

Hi Sue, that again is a great question. If phytophthora is in the soil, you want plants resistant to that problem. I'm assuming you want a short, hedge-like plant. I can tell you to stay away from azalea, holly, camellias, pieris (also called Andromeda) and junipers! According to the government site, most conifers should be avoided too.

So maybe it's time to try a native hedge? The third and fourth sections of the following brochure are suggestions for large shrubs and a small/medium shrubs.
https://www.oregonmetro.gov/sites/default/files/2020/06/30/native-plants-for-Willamette-Valley-yards-booklet-high-res-20200107.pdf

You can also ask at your local (or favorite) nursery for suggestions of phytophthora resistant shrubs. Be sure and tell them about the boxwood experience!

Good luck with your new border.

Thank you!!