By Scott Aker
Special to The Washington Post
Thursday, May 7, 2009
Q I have two sand cherries that did well for six years and then suffered dieback. Last summer, sap began to emerge from their trunks. Were the stems nibbled by rabbits or squirrels, or is this a result of disease or insects? Recently a Bradford pear that was shading them came down, exposing them to more afternoon sunlight.
A Sand cherries do not thrive in our region and are not frequently grown here as a result. As the name implies, they grow well in sandy soil and are found near the beach and in sandy glacial outwash in portions of New England and other northern states.
Sand cherries dislike soil that does not drain rapidly, and they can't tolerate a lot of heat during the summer. They also struggle in shade or in competition with trees, so the loss of the pear might be a good thing. In the short term, however, the brighter sunlight may stress them since they were growing in a partially shaded location.
Your shrubs may be infected with a fungus that causes cankers just under the bark. Fungicides don't really control these types of fungi. They are opportunistic invaders that are favored by drought and heat stress. The sunnier conditions at the hottest part of the day may have created heat stress sufficient to cause cankers.
There's not much you can do. You could cut the shrubs to the ground and see whether new growth is able to sprout, since it is likely that the branches above the cankers will die. You could also try planting a substitute. A large shrub named Photinia davidiana (formerly known as Stransvaesia davidiana) is wonderfully adapted to our climate and more tolerant of stressful conditions. It has red fruit rather than the black of the sand cherry, but the flowers and leaf texture are similar. It is very attractive in fall and winter when the leaves persist and turn various shades of red.
Are there any hardy varieties of gardenia that would survive outside in Arlington?
I have grown Chuck Hayes, Kleim's Hardy and Heaven Scent. Both Chuck Hayes and Kleim's Hardy have done well despite a harsh winter. My Heaven Scent experienced a bit more dieback, but because it was planted late last fall and is still very much alive after this long, hard winter, I think it will ultimately perform very well.
Chuck Hayes is a more open and tall plant than the others, but it blooms sporadically from June to frost. It has double flowers. Kleim's Hardy is very compact and covers itself with single flowers in spring. I have seen it in local garden centers, and it is available from many online and mail-order nurseries. Heaven Scent is compact and has interesting fruits that develop an orange hue in autumn. It is being marketed through Lowe's and Home Depot.
Scott Aker is a horticulturist at the U.S. National Arboretum.