By Dr. Leonard Perry, Horticulturalist in Residence
Do you have some roses that you would like to have survive the upcoming winter, if at all possible, and particularly if new plantings? Or, are you one of those who had roses going into last winter, only to have many die while those of your neighbor lived? If either of these fits, you might consider mulching and mounding this fall as is done in the King’s Garden.
A mulch will not only keep the soil warmer than unmulched soil, but also will prevent rapid fluctuations in soil temperatures which lead to soil heaving. Snow is the best mulch but, as we know, cannot always be counted on. So other materials must be used.
A good mulch will settle lightly on the soil surface without excessive packing (this rules out most oak leaves), cause no harmful effects (such as from diseases or weed seeds), and be reasonably attractive and priced. Mulches derived from plants also add organic matter to the soil. Examples of good organic mulches are peat moss, weed-free straw (not hay, which is often weedy), cut evergreen branches, bark mulch, or wood chips.
Mulches should be piled at least a foot deep around plants, and not before mid-November, as roses need cool fall temperatures to develop some winter hardiness. Mulch much later and you may have to contend with snow first, and valuable ground heat will have been lost.
Mounding also may be used to protect roses during winter, simply mounding loose soil or compost a foot or more high around the base of the plant. Use loose sandy or loamy soil, as dense clay soil may cut off the oxygen supply to the roots, resulting in injured or dead plants. Mounding is preferable over mulches if you have mice that may live in organic material and chew on the rose stems over winter.
Climbing roses may be protected by removing the canes from their supports (keep this in mind in the spring when tying them up, for easy fall removal), then laying them on the ground. Use a wire hoop or similar device to hold them in place. Lay a piece of burlap over the canes to protect them during the spring uncovering operation, then mound soil or compost or organic matter over the canes. Uncover the canes when they begin to grow in spring, checking them in early April or shortly after the snow melts.
Mulching or mounding protects roses in a couple of ways. Roses vary greatly in their hardiness, depending on species and cultivars, with the more hardy not even needing protection. You may find a list of some of these on my Perry’s Perennial Pages website of past
Vermont rose hardiness trials (pss.uvm.edu/ppp/rosedata.htm). There, also, you’ll find a leaflet on some of the heirloom or old-fashioned species roses (http://pss.uvm.edu/ppp/articles/rosespecies.html). Some of these rose species are much hardier than many of the modern hybrids.
Most roses also are grafted onto a hardier wild rose “understock.” Where they meet—the graft union– is the swollen area you can find at the base of many rose plants. It is often tender and susceptible to winter injury, so needs protection. Many recommend to even bury this graft union below the surface when planting, which also will help prevent undesirable sucker canes arising from the wild rose understock.
Before mulching or mounding roses in mid to late November, finish fall cleanup. Remove all plant debris and diseased parts. Pruning, although usually done in spring, may be done now to remove diseased or dead stems and to make the plant easier to mulch. Even with protection, canes may have some dieback and need further pruning in the spring.