Us gardeners feel like we’re getting the short end of the stick this spring with the seemingly endless rain and cool temperatures, but there’s another dilemma I’ve been asked about multiple times: What the heck is going on with the rhododendrons?
Curled brown leaves can be found on more than 50 percent of the bushes I’ve observed, and some folks believe they may have lost their entire shrub. After the third person asked me what I knew about this, I became obsessed with checking out every rhododendron I passed by. Do you think my rubbernecking would qualify as distracted driving?
Anyway, what I’m mostly seeing is just sections of the shrubs have browned. I had my own suspicions about the cause of this winterkill but thought I’d confer with a couple knowledgeable folks to see if I was off-base. My worst fear was some type of blight. Some browning of leaves over the winter is normal but what I’d been seeing made me wonder if the shrubs had actually become sick.
I spoke with both Matt Wasserloos, the Keene store manager of Achille Agway and Steve Roberge, a forester from the UNH Cooperative Extension in the Keene office. Neither Matt nor Steve mentioned anything about blight, thank goodness.
Rhododendrons are broad-leafed evergreens and particularly the varieties with larger leaves are susceptible to winter damage. Though we saw very few days that were 10 below zero or colder, we did have periods of sustained low temperatures in general and there was also lots of wind and ice this past winter. Very cold, severe winds can cause significant desiccation of leaves.
Also, even though they’re dormant per se, they’re still losing water through their leaves on slightly warmer, sunny days and with the ground still frozen, they’re unable to take up water through their roots to replenish. Repeated cycles of freezing and thawing days can also do damage.
Think about the old gardening rule of waiting ‘til the ground is frozen before applying winter mulch to some of your more tender perennials for protection. Once the ground is frozen, you’re actually insulating the plants from warming thaws that come too early, only to then be plunged back to below freezing temperatures.
So, what to do with those branches of withered brown leaves? I usually wait until I prune back the dead canes on roses and if there’s no sign of replacement leaves coming in on the rhodies, I cut them back.
Well, Steve recommends perhaps even a bit more of a wait-and- see period. Chances are good that the buds are still viable at the ends of the branches so they should open with new leaves and all along the rest of the branch there may be immature leaf buds that will now develop.
Most evergreen broadleaf shrubs are fairly slow growers, so you might be stuck with significantly smaller and even misshapen plants longer than you’d imagine in the garden. I looked online for any preventative measures we can take to avoid this winterkill and Emma Erier on the UNH Cooperative Extension blog advised some common-sense steps: choosing the right varieties for our zones 3-5 climate; planting in a semi-shaded spot, protected from harsh winter winds and sun; as well as possibly wrapping or boxing the shrubs in burlap.
I also have seen anti-desiccant sprays at local garden centers that put a somewhat waxy coating on the leaves of evergreens. I have a bottle somewhere here in Dublin, but I don’t remember ever trying it on outdoor shrubs. I think I initially bought it to lengthen the suppleness of holly and laurel leaves gathered for holiday decorating inside the house.
So, just like waiting for warm rays of sun this spring, we’ve got to be patient with our evergreens. And, if you have a rhododendron that turns out to just not be salvageable, think of the opportunity. Off to the nursery you will go to see what fabulous new shrubs await!