The Bay Gardener by Dr. Frank Gouin
Are You Killing Your Boxwoods?
These evergreen imports are picky customers
Boxwoods are not difficult to grow, especially if you ignore them. More people kill boxwoods by mulching than by any other cause. This species is very shallow-rooted; covering their roots with mulch will cause root suffocation. Worse still, if the mulch is uncomposted wood waste that includes double shredded hardwood bark, colored mulches or wood chips, these mulches will compete with the boxwood roots for nutrients.
Boxwoods require well-drained soil and will not tolerate frequent irrigations. Automatic lawn sprinklers are another common killer of boxwoods. Lawns require more and frequent irrigations than boxwoods. If the boxwoods are being irrigated as often as the lawn, they are likely to become susceptible to Phytophtora root rot. Boxwoods are much more tolerant to drought than they are to wet soil conditions.
If you are growing boxwoods in with your azaleas, you are likely to have boxwood nutrition problems especially if the azaleas are growing well. Boxwood plants prefer a soil pH of between 6.0 and 6.5 while your azaleas prefer a soil pH between 4.5 and 5.5. The only method for raising both species together is to add sufficient compost to the soil to raise the organic matter concentration to above 5 percent and raising the pH of the soil to near 5.5. If you wish to grow an evergreen with your azaleas, substitute Japanese hollies, which perform best at a pH similar to those of azaleas.
Boxwood plants also have a very high requirement for magnesium in the soil. Pale green to yellow-green leaves generally means that the magnesium concentrations in the soil are low. The only means of making this determination is to have the soil tested. Take soil samples around boxwoods under the drip line in the shade of the branches at a depth no greater than three inches.
By the way, all boxwoods originated in either Europe or in Asia. There is no such plant as American boxwood.