This is the showiest time of year for the showiest members of the Ericaceae, or heath family: the Rhododendrons, azaleas (which also belong to the genus Rhododendron), and mountain laurels (Kalmia species). The picture above shows a Rhododendron planted in front of my house long before we moved in 20 years ago–when they’re happy, these plants really show it, and they last pretty much forever.
The Ericaceae is a large plant family comprised of about 125 genera and 4,000 species. Most are broadleaf evergreen shrubs. Just a few of the many members of this family you may be familiar with, in addition to Rhododendrons and azaleas and mountain laurel, are blueberries and cranberries (genus Vaccinium), Labrador tea (Ledum groenlandium), heathers (Erica and other species), bearberry (Archtostaphylos uva-ursi), Andromeda (bog rosemary), and Leucothoe. All are excellent native evergreen shrubs for the garden.
As a horticulturist who designs sustainable gardens, I think of members of the heath family when I am confronted with a challenging site. In general, these plants not only tolerate but actually thrive in poor, dry soil, as long as it’s sufficiently acidic. They evolved in marginal conditions–think of a heath or the rocky side of a mountain. To extract the necessary nutrients from the soil, ericaceous plants coevolved with miccorhizzae, or microscopic fungi that live within the plant’s cells in a mutualistic relationship. So don’t overfeed or water plants in this family (which, in most cases, means don’t feed or water them at all once established), but do be sure that the soil is sufficiently acidic.
That often requires a bit of soil emendation. The soil is this area is acidic, but it’s usually not quite acidic enough for these plants. I use HollyTone about once every two years to keep my Rhododendrons and mountain laurels happy (not twice a year as directed on the package). If the leaves look yellow, try a weak feeding. If they’re nice and green, don’t bother. (This is the only soil emendation I ever do, and it’s necessary because whoever planted my rhodies and mountain laurel chose a spot where the soil isn’t quite acidic enough.)
Mountain laurel, which is in bloom right now, is my absolute favorite native shrub. Consider it if you need a screen or a foundation plant or to fill in a bare spot (many different size plants are available within the Kalmia genus). Mountain laurels are readily available in garden centers. These are blooming outside my front door right now. They’ve been there for more than 20 years and always look gorgeous:
To ensure that they bloom abundantly every year, remove the spent flowers. And notice the spots on some of the leaves in the photo above? that’s a mild virus that will not harm the plant. Spraying is quite unnecessary.
And finally, here’s a lovely Rhododendron in bloom outside our front windows. I wish I knew the variety: