For folks in warmer areas, like the warmer parts of zone 6 and throughout zone 7, where the ground freezes down a few inches and then repeatedly thaws and refreezes throughout the winter, the purpose of winter cover would be the same, i.e. to keep the roses from repeatedly freezing and thawing, but in this case it would be to insulate them to prevent them from freezing in the first place. It really amounts to the same thing, however.
Given these principles, when to uncover your roses should be obvious, wherever you live. It is simply when the danger of freezing and thawing has passed. Around here, that usually occurs sometime in the first two weeks of April but virtually never in March, regardless how warm it might get for a few days. Let me give you a recent example. In the spring of 2012 we had 70 and 80 degree weather in mid-March causing fruit trees to blossom etc., but in the next week we had 10 degree weather followed by at least two weeks of below freezing weather. This caused the loss of almost the entire apple crop in Minnesota and Wisconsin and virtually the entire cherry crop in western Michigan. If you had uncovered your roses in March 2012, thereby allowing them to thaw out, you would have suffered severe damage when they froze again.
I realize that it is very tempting to uncover your roses when it first warms up in the spring. If you use the leaf bag method, which I have advocated in my blogs, you can choose to partially uncover your roses by rolling the leaf bags back but leaving them ready to replace, if the weather turns cold again. This approach allows the plants to begin thawing and to soak up spring rains, while keeping your options open for easy recovering. I would say that I use some form of this approach almost every year, especially when it starts to rain (vs snow!).
Today, April 1st, it was 82 degrees and we are expecting thunderstorms tonight so I decided to go out and roll the bags off my roses, while keeping them close-by, if I have to roll them back
Wherever you live, my suggestion is to watch the seven-day weather forecasts in early April and try to determine when your nights stay consistently above 25 F (-4 C). If you keep the mounds around your plants, even if you pull the bags back, temps down to 25 F will not refreeze your plants. If you are in doubt, just keep your plants covered until mid-April, around here. It won't hurt them.
And here's a quote from Paul Douglas' weather blog today:
"Another Relapse After a May-like temperature swoon today temperatures cool off later this week, a taste of early March shaping up for early next week with readings struggling to reach 40F Monday and Tuesday. European guidance is even hinting at a rain/snow mix, especially north of the Twin Cities. Don't rule out more slush before the daffodils arrive."
On the theory that a picture is worth a thousand words, here is how my beds look after rolling back the leaf bags this afternoon. Note that the roses still have plenty of leaves and mulch around them and the bags are right there if I want to roll them back over the plants. Incidentally, most of those leaves around the plants will get pushed back in the bags and be transported to my compost pile, when it's time to finally uncover the beds, which will probably be in 10 to 14 days, when Paul Douglas is no longer warning about slush and freezing temps.
I always laugh when I hear someone say you should prune your roses when the forsythia blooms. Suppose it had bloomed in mid-March 2012, as mentioned above, when your roses were still covered? When the forsythia blooms really has nothing to do with when you should prune your roses. Pruning for me is a two step process. First, right after I uncover my roses (i.e. mid-April), I begin by cutting off all the dead wood, right down to where the canes begin turning green. This is a very rough, quick cut that I do with my battery-powered Black & Decker hedge trimmer. I don' t worry about rough cuts on the canes because I know I'm coming back later to make my final pruning and shaping cut. All I want to do is to take off the "overhead" of dead wood to clear the way for new growth that will come from the green canes. Once I can see that nodes on the green canes are starting to swell, in anticipation of setting new leaves, then I begin my second cuts to shape the plants and eliminate any weak, wispy growth from last year.
So, in summary, you should first cut off all the "overhead" dead wood and then, when the plants show signs of growing, make your second cut and seal it off to stop saw-fly wasps from burrowing into the fresh wood to lay eggs. I use Elmer's school glue for my sealant, which works very well and is quite inexpensive. And the forsythia may or may not have bloomed when you finish. We're talking roses here, not flowering shrubs!
April 1, 2015