Winter-Protecting Roses with Construction Blankets

This blog post is a joint effort between Deb Keiser, Rose Specialist at the Munsinger and Clemens Gardens in St. Cloud, Minnesota, and Jack Falker, “The Minnesota Rose Gardener”.

In the last few years a new method of winter-protecting roses has emerged in Minnesota, which we believe has application beyond the so-called “cold zones” of the Upper Midwest.   At the Virginia Clemens Rose Garden in St. Cloud (Zone 3/4), Rose Specialist Deb Keiser has stopped using the “Minnesota Tip” method and is now winter-protecting both her public and personal rose gardens with the insulated blankets cement contractors use in the winter to cure concrete in sub-freezing temperatures.  Construction blankets typically come in 6 X 25 or 12 X 25 foot sizes and have an insulating R-value of 7.5.  (We believe the R-value is important and blankets with less than an R 7.5 value may not be as effective.)

In earlier articles on preparing roses for winter: “Winter Protecting Your Roses”

(http://jack-rosarian.blogspot.com/2013/09/winter-protecting-your-roses.html) and “How Winter Affects Roses” (http://jack-rosarian.blogspot.com/2013/12/how-winter-affects-roses.html), I have advocated the following sound horticultural practices, in lieu of the labor-intensive Minnesota-tip method.

• Plant the bud unions of hybrid tea roses 3-6 inches below the soil surface and the crowns of own-root roses at similar depths to protect from freezing and thawing. 
• Give your roses a six-week potassium feast to harden off their canes for winter.
• Use at least 3 inches of wood chips in your beds, year-round, and more around your roses in the fall.
• Mound your roses with good compost in the fall, including lots of coffee grounds.
• Tie up your roses in bundles and cut them back to about 8-12 inches, when they stop blooming.
• Strategically place rodent bait containers around your roses to protect against vole damage.
• Cover your roses with half-filled leaf bags or wire cylinders of leaves, when the ground first freezes or snow begins to accumulate, whichever comes first.  Hay can also be used for this purpose if it is packed closely around the mounded plants and held in place by bags or fencing.  Straw is less effective because it is less substantial and does not compost well.
• Construction blankets are our other alternative, as we will discuss below.

The final steps above insure that your roses will not freeze and thaw repeatedly during the winter.  In the "warmer" cold zones, i.e., zones 6 and 7, insulating your roses, as described above, should have the effect of not allowing them to freeze in the first place; different than our expectation in zones 3, 4 and 5.

Enter Construction Blankets!

Deb and I agree on virtually all of the above steps, but she believes that using construction blankets, instead of leaves or hay, for the final protective cover in the fall is a better solution.  Seeing is believing, and I believe that Deb's practice, which she has been using for upwards of ten years now, has applicability not only in zones 3, 4 and 5, where the ground freezes solid every winter, but especially in zones 6 and 7 where constant freezing and thawing is endemic to most winters.

In late October, when the roses have stopped blooming (perhaps early November in Chicago or early December in zone 7), Deb mounds her roses and cuts them back, as mentioned in the bullet points above. If it is dry, you can continue to water the plants or, if you are still in the process of applying liquid potassium (which we highly recommend), that watering will suffice. Deb puts the blankets on her roses just before night-time temperatures go into the low 20s or snow starts to accumulate, whichever comes first.  This is all very similar to the practices cited in the bullet points above. 

For those of you not accustomed to cutting back your roses in the fall, please be assured that there is no downside in doing this, when they have finished blooming.  When roses are well mulched and protected all winter, they grow very aggressively in the spring, which is the strong growth you really want for the new season ahead (see the spring pictures of Deb's garden below).

Here is how the Virginia Clemens Rose Garden looks after Deb has cut everything back and begun covering with the construction blankets.  Note that she is careful to secure the blankets around the roses with lots of bricks.

And below is a picture of the Virginia Clemens Rose Garden fully covered.  Note that some of the trees still have a few leaves, so you can gauge the equivalent time where you live.  It starts to get cold in St. Cloud in mid-November, so Deb is striving to get everything covered, before the nights go into the low-twenties .  By the way, those Minnesota rosarians who still tip their roses are digging trenches and tipping their roses into them in mid to late October, which seems early to us, given that their roses have often not finished blooming, but that's how that process works.

And below is a picture of one of Deb's home rose gardens, taken in 2 degree weather on November 23, 2013. Note that 2 X 4s can be used to secure the blankets, as well as bricks.  All of this disappears, of course, once the snow covers everything.

And the Ground Doesn't Freeze!

Given the fact that the ground freezes several feet down in a typical Minnesota winter, regardless of snow cover, and that both mounded/leaf-covered roses and Minnesota-tipped roses are thereby frozen solid and simply protected from thawing and refreezing, I naturally assumed that the Virginia Clemens beds above would be similarly frozen and protected from thawing until spring.  I was, therefore, somewhat skeptical when Deb and her husband Dave Keiser told me in mid-January 2014, at the Twin Cities Rose Club meeting, that they believed neither the roses in the Clemens gardens nor the roses in their personal gardens were frozen under the construction blankets.  Keep in mind that the low temperature had already been -25 F in St. Cloud this winter and that there was more than a foot of snow on the gardens.

So, knowing that we were going to jointly write this article, Deb suggested that we should clear away the snow from the corner of one of the above beds and take a peek under the blanket.  That sounded like a fun way to play in the snow and, since the temperature was actually going to moderate for a day or two, I drove up to St. Cloud on January 24th and we initiated our little experiment with a couple of shovels and a commercial-grade thermometer to measure soil temperature under the blankets.  Here are pictures of the two of us "gardening" on that +30 F, late-January day:

 Here's Deb clearing away the snow from the edge of the covered bed.

Here's Jack reaching as far under the blanket as possible with the thermometer.  This is where we discovered that the ground was actually loose and friable under the blankets.  

We were actually able to stick the thermometer a couple of inches into the unfrozen ground and found it to be 33 and 34 degrees, in two separate measurements.

This is an impressive result, given that we were measuring a zone 3/4 garden in January, when the low temperature had been -25 F.  Interpolating this result to "warmer" cold zones such as 5, 6 and 7, it is easy to see how using construction blankets would be a relatively easy, sure-fire way of protecting sensitive rose gardens in any winter weather situation, perhaps especially in the warmer cold zones that experience constant freezing and thawing all winter.

Here are Deb's comments about what she is winter-protecting in both her personal and the Virginia Clemens gardens:  

"... At home I cover zone 6 & 7 grafted hybrid tea, floribunda, grandiflora, and shrub roses, a few own-root hybrid tea roses, miniature roses, zone 5 Flower Carpet shrub roses and David Austin English roses, Tess of the d'Urbervilles and Benjamin Britten.... At work I cover zone 6 and 7 grafted hybrid tea, floribunda, grandiflora and shrub roses, some own-root hybrid tea, floribunda and shrub roses, miniature roses, a bed of David Austin English roses, a bed of Buck roses and Knock Out roses...."

Deb further points out that all of her grafted roses are planted with their bud unions about 3 inches below ground level.  This is very important in any garden that experiences even the mildest of winters.  In our considered opinion, there is no justification for planting grafted roses with bud unions above ground level in any garden location.

Incidentally, Deb also puts potted miniature roses and tender perennials under the blankets in the Clemens garden.  If the pots are too large, the plants can be removed from their pots, laid on their sides, and mulched before covering with the blankets.  While Deb currently brings all of the garden's potted tree-rose "standards" into the garden's greenhouse, she believes that standards could be wintered under the blankets, as well, so long as the plants are laid on their sides and fully covered with mulch, before the blankets are applied.

And here's the proof of the pudding: pictures of Deb's gardens in early spring, when the blankets come off. Note that the roses have already started to grow under the blankets; ready to prune and take-off toward their first bloom cycle.  Once again, for those of you in the warmer cold zones, we do not believe there is any disadvantage in cutting your roses back and covering them thoroughly in the fall.  

Construction blankets are in common use by cement contractors in just about any area that experiences winter weather.  Apparently, most contractors rent their blankets, as required, and the best place to acquire them, either used or new, is likely to be rental companies that cater to those contractors.  Perhaps the best reason for this is that the blankets have to be stored someplace dry for more than six months of the year, which presents a potential storage problem for both contractors and gardeners alike. In Deb's case, she acquires most of her blankets in good, used condition from a rental firm in St. Cloud.  She also has the distinct advantage of having several, roomy, municipal buildings for storing her Virginia Clemens blankets in the summer time.  I might also mention that the Munsinger and Clemens Gardens, have a beautiful, large, new greenhouse, in which a large variety of roses and many other plants are profusely blooming all winter long. So who needs winter protection in Minnesota, when you have a climate-controlled greenhouse?  But that's another story altogether!

Both Deb and I would be happy to answer any questions you might have. 

You can reach Deb at deb.keiser@ci.stcloud.mn.us;

and you can reach Jack at  jack@falkerinvestments.com .

Deb Keiser and Jack Falker

February 4, 2014