Winter-Protecting Your Roses
Everyone in Minnesota knows they have to do something to winter-protect their roses. However, not everyone seems to know exactly what they’re supposed to accomplish and, thus, what the best method might be. So let’s start with the one basic principle that applies in all cold zones, i.e. USDA Zones 3, 4, 5 and parts of 6, and to virtually all types of roses, whether they be hybrid teas or shrubs; grafted or own-root.
Fact: The primary objective of winter protection in the cold zones is to keep your roses frozen, not to keep them from freezing. There seems to be a lot of confusion about this and, unbelievably, we still have nurseries selling styrofoam rose cones, which serve as little ovens in the winter, when the sun shines on them, causing plants to freeze and thaw repeatedly, thereby killing them.
There are two basic ways of keeping roses frozen where we live: (1) the Minnesota Tip and (2) mounding with compost and insulating with leaves or hay. Let’s be clear about the “tip” method: When you tip your roses over in a trench, bury them in dirt and compost, and put leaves on top, they are definitely going to freeze solid in the ground, as the frost permeates down several inches. In fact, many Minnesota-tippers soak their tipped roses, before turning off their water for the winter, so they will be contained in blocks of ice. In other words, the objective of the “tip” method is to freeze roses solid and keep them frozen until spring
I personally believe that keeping my roses standing upright and firmly planted, while mounding and insulating them, is the best way to winter-protect. I tipped my roses for many years but always felt that it was not horticulturally sound to partially uproot the plants and cover them with dirt in mid to late October, when many of them were still in bloom. The longer I did it, the more my gardening instincts (not to mention my back) kept telling me I should be doing something different. Take a look at my August 2012 Minnesota Rose Gardener blog post "No Tipping Please”:
Many people, who have been tipping their roses for years, feel trapped in the procedure because the bud unions of their grafted hybrid teas are above the surface of the ground. This is a basic problem, which is endemic to the tipping procedure. For a variety of sound horticultural reasons, the bud unions of grafted roses and the crowns of own-root roses should not be above ground, regardless of where you live, warm or cold. My advice to these folks is: Instead of tipping your roses this year, dig them out entirely, taking a good root ball, heel them into a trench, a foot or so deep, and cover them with a good layer of dirt and mulch (to keep them frozen). Then in the spring replant them in the same place, except this time plant them with the bud unions several inches below the surface. If your garden is large, you might do this in stages, some this year, some next year etc. Another alternative might be to raise the level of soil in your beds so that your bud unions are at least slightly below grade.
With your roses properly planted, here is what I recommend for winter protection. First, in mid-September and for six successive weeks, give your roses a potassium feast to help their canes harden off, before the first hard freeze. It’s too late to start the feast this year (I’m about to do my fourth application) but I believe potassium is important in winter protection. For future reference, here is the address of my most recent blog on the potassium feast:
Next, gather any wood chips or other clean mulch in your beds and mound it around your plants. Then, mound several shovels of compost around every plant, so that the plant crowns are thoroughly covered. My compost is primarily shredded oak leaves from last fall and hundreds of pounds of composted Starbucks coffee grounds that I collect regularly. This compost is full of worms and worm castings, so it's just what the roses need in the spring, when I spread out the mounds and work the compost into the ground.
Next, when it starts getting cold and your roses have stopped blooming, cut them down to about 12 inches and bind them into tight bundles. One other thing you might do, especially if you’ve had spider mites this summer, is to strip the leaves off the plants and spray them with horticultural oil. (Don't worry, you're not losing anything here; what you want is the strong new growth you’ll get in the spring.)
The final step is to prepare enough half-full plastic leaf bags to cover each of your roses. (Don't use the new compostable bags; they break down over the winter and leave you with piles of leaves to clean up!) Now, wait until the ground freezes and, with the objective of keeping your roses frozen, slit open the bottoms of your leaf bags and shove them down over each of your tightly bundled plants, flush with the mounds.
So, can you see how this approach will keep your roses frozen? When you start to carefully roll the bags off your roses in the spring (to keep as many of the leaves in the bags as possible for disposal or mulching), you will find that many of the bags are still frozen to the mounds and that your roses are encased in blocks of ice; exactly as you wanted them to be. In fact, depending on how quickly it warms up, it may actually take longer for these mounds to thaw than roses that have been tipped.
Regardless of how you choose to winter-protect your roses, please keep firmly in mind that your objective in the cold zones is to keep them frozen all winter. The other alternative, of course, would be to move to a warmer zone, where your objective would be the opposite, i.e. to keep your roses from freezing in the first place. No such luck for me!
Jack Falker (@mnrosegardener)