Regional Growing Guide: Western Mountains & High Plains
From the eastern slopes of the Cascade and Sierra ranges through the High Plains, this generally arid region battles bitterly cold winters, blustery spring winds, little rain and sometimes brutal summer heat. The soil presents challenges, too, be it alkaline, sandy, clay or infused with salt and boron. Fortunately, the severe climate poses few insect or disease problems. But the roses that thrive here must be cold hardy and survive wild swings in temperature. They often bear strong, leathery leaves to resist desiccation. They also appreciate regular irrigation, heavily amended soil, a thick layer of mulch and protection from the wind.
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Ready, Set, Prune!
Fall is the time to prune roses back to knee high. The rule of green thumb is that when roses have seen three consecutive hard freezes in a row, they're dormant. A hard freeze is defined as at least 28 degrees. If, by Thanksgiving or so, you haven't had temperatures that cold, you can prune anyway.
Why knee high? And whose knees, anyway? That's just a general way of saying you can lop off the rose canes at about 2 feet high - all the same height, nothing fancy right now. Then strip off all remaining leaves. If your weather has been really frosty, the leaves should snap off cleanly. If not, snip them off with a pair of small pruners.
Why Prune in the Fall?
Fall pruning is preventive medicine for roses. When we remove that lanky top growth, we take away the wind's ability to rock the roses loose from their moorings.
When we remove all the leaves, we ensure that the roses will go into dormancy even if they haven't seen those days with hard freezes. And we eliminate a lot of hiding places for fungi and insect eggs.
Put everything you removed into a trash bag, then rake up all the rose debris underneath the plants and add that to the bag. Don't compost it. The insects and diseases on that rose debris can survive composting.
Bring in the Fresh Mulch
You want to make sure there is at least 3 inches of protective mulch covering the soil over the entire root zone. That's in addition to the 6 to 12 inches or so of mulch (bark chips, straw, or a mixture of compost and soil) you're going to pile up over the graft and as high on the canes as you can. That will protect the roses from winter's fluctuating temperatures by keeping them cold. You don't want the ground to thaw in mid-January and have the rose get the idea that it's time to start growing!