There are three general reasons why boxwood leaves turn yellow:

1). If your boxwoods were not covered during this past winter season, the leaves might have experienced some type of sun scalding. The three boxwoods might not have been sufficiently watered in the fall. They also might not have developed a good root system as winter approached. Often times with sun scalding new foliage eventually appears. I would wait for another couple of weeks before concluding that the new boxwoods should be replaced. Keep watering them as well. If they do recover, consider wrapping them with burlap this coming fall.

2). Root rot is sometimes the culprit. It is a fungal infection, most commonly associated with hot, humid conditions. If this is the case, there is not much you can do in terms of remedial action.

3). Iron deficiency can also cause leaf yellowing. This is a relatively uncommon situation. However, in the event that this is the problem, iron can be added to the soil via the application of blood meal and/or chelated iron powder.

See the following for information on these and other points:

https://plantophiles.com/gardening/why-are-my-boxwoods-turning-yellow/

https://www.nola.com/entertainment_life/home_garden/article_cb3d4fb2-3de7-50c2-929c-202b0e9df8b8.html

https://www.gardeningknowhow.com/ornamental/shrubs/boxwood/yellow-or-brown-boxwoods.htm

https://pallensmith.com/2014/05/22/iron-deficiency/ - :~:text=And just like us, if,made apparent by yellowing leaves.

https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1415.pdf

https://greenupside.com/how-to-add-iron-to-garden-soil/

Bottom line: give your boxwoods a little more time before considering replacement. If sun scald is the cause, new foliage should appear. If root rot is the cause, replacement may be necessary.

One another thing to determine is if the boxwoods are alive or not. Here’s a simple way to do that. On different branches of each boxwood, gently scrape off a small portion of the bark. If the underlying tissue is greenish-yellow, the branch is alive. If the underlying tissue is brown, the branch is dead. If you determine that just one or two branches are dead, prune them out. If you can’t find any living branches on a plant, that plant needs to be replaced.

Good Luck. Get back to us with any additional questions.