Ah, the magic and mystery of plants! Biennials beguile us and fool themselves into believing they're into their second year of growth after a brief spring cold snap. And right now some are snapping their twigs at us because the days are shorter, and they're blooming their buds out.
Usually short day plants bloom early in spring, before days grow long. Daylight did grow long, and now that they're shorter again some plants decide it's time to bloom again.
Rhododendrons and azaleas are particularly susceptible to this second bloom, especially if they were properly deadheaded after their first bloom. The bud for next year's blossom lies immediately behind this year's now spent blossom, so removal of the spent flower prepares the way for the next blossom. That requires that you work with care in removing the spent blossoms, lest you wrest the bud loose too.
Apple trees often bloom again in autumn, sparsely, in response to length of daylight.
Another explanation for rhododendrons' blooming in fall is that your shrub may be a reblooming azalea, not a rhododendron, according to Anju Lucas, head of perennials for Edwards Greenhouse. They are the same genus: all azaleas are rhododendrons, but not all rhododendrons are azaleas.
There are at least two varieties of reblooming azaleas on the market, "Encore" and Proven Winners' "Bloom-a-thon." Like rhododendrons, they are evergreen. Evergreen azaleas are different from rhododendrons in these ways: rhododendrons have 10 or more stamens, azaleas usually have five. Rhododendron leaves are often scaly or have dots on their undersides, but azalea leaves never have scales, and are usually pubescent (fuzzy).
Azalea flowers are shaped like funnels, rhododendron flowers are more bell-shaped. These differences are not sufficient to give you a "drive by" identification, but growing familiarity with one or both species should.
Right now is a great time to do some needed work on your rhodies or azaleas: mulch them. Both have clumps of fine fibrous roots that are tender and touchy. They must have good drainage and at least slightly acidic soil.
Mulching at this time of year will protect those roots from cold temperatures, while mulch in summer insulates against excessive heat. Pay close attention to mulching materials, however, especially for these acid-loving shrubs. Peat moss, ground bark or pine needles are excellent mulch for them. Don't use grass clippings or animal manure, for they are too high in nitrogen for your shrub.
Leaves may mat, and ultimately block natural moisture from penetrating to the roots, but if they're shredded before being used as mulch, they may do.
Mulch materials will hold sufficient moisture in the soil for the shrub, and gradually decay to humus that feeds the plant without over-stimulating it. This mulch must be renewed annually, at least.
If you're planning on planting a rhododendron, it's best to carefully select the site for planting. Michael Dirr, one of the top experts on woody plants, writes of rhododendrons that "inadequate drainage is the most prominent factor limiting growth. If poor drainage does not directly kill plants, it predisposes them to insects and diseases such as root rot."
Select a planting site that has dappled or light shade for at least part of the day. These shrubs require little care, little fertilizer and modest amounts of water once they're properly situated. If their root mass is a dense circular mass when removed from their containers, carefully cut into them vertically about every 90 degrees and tease the roots apart.
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