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Monday, May 15, 2017


Monday, 8:00 AM.  46 degrees F at the ferry dock and on the back porch.  Wind variable and calm, the sky darkly cloudy, the radar showing more rain clouds approaching the Bayfield peninsula after a trace of wind driven rain earlier.  The barometer is more or less steady, at 29.99" of mercury.  Temperatures should reach the high fifties with rainy weather through Wednesday, then cool into the 40's with no rain.  The rainfall and cool conditions are great for establishing the extensive rock gardens we just planted on Chequamegon Road at the lake front.
    There are a number of cold hardy species, varieties and hybrids of rhododendrons and azaleas.  My recorded blooming dates for the hybrid  PJM Rhododendron are as follows: 5/10/16; 5/07/15; 5/03/12. Pretty consistent and right about  on time this year.
   Both rhododendrons and azaleas are members of the genus Rhododendron, the main difference is that the former are are evergreen, retaining their leaves in the winter, and the latter are deciduous.  Wisconsin has only one native species of Rhododendron, and that a very rare relict of glaciation that grows in small, isolated populations north of Madison in the Dells of the Wisconsin River. and on the cliffs of the Kickapoo River.  R. lapponicum, the Lapland rhododendron, is a disjunct, far out of its native range a thousand miles north. It was left there millennia ago by the retreating glaciers (thank heavens for global warming).
   The University of Minnesota has introduced cold hardy azalea hybrids, the Northern Lights series, that can withstand northern Wisconsin winters, but as do all Rhododendrons they require an acid soil and some care in location and planting. Being near the insulating waters of Lake Superior is of course most helpful.  A few other species and hybrids are also hardy, including PJM, a selection of the Korean rhododendron. There are also some hardy introductions from Canada and Finland.
   I have a protected location where I am growing some of the Northern Lights hybrids and other Rhododendrons. Both 'Golden Lights' and 'Rosy Lights' have established well and bloomed every spring, but they need some acidifying fertilizer.  Also, this far north Rhododendrons should probably be planted in full sun, whereas further south they should be in a shady location.
   For more information on hardy Rhododendron, see Azaleas and Rhododendrons for Minnesota, by Michael Zins, University of Minnesota Extension.

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