At this time of the year, ordinarily, roses have entered dormancy. This status, characterized by stopped growth above ground, protects the rose from winter freezes and provides a rest period that supports the plant’s longevity and productivity. Hothouse roses subject to year-round harvesting of blossoms have shorter lives and fewer blossoms, compared to the typical garden rose.
During dormancy, the rose reduces its metabolism, holds its fluids and nutrients away from the stems and stores them the core of the plant. This is the rose’s defensive position, designed to avoid a possible freeze of liquids in the stems.
The plant continues to develop below ground: root growth continues during the winter months and is important for newly planted roses.
Gardeners in the world’s colder regions worry that an unusual warm spell in the late winter or early spring might cause their roses to “break dormancy.” The plants could produce new growth that would be killed by a late freeze.
In more temperate climates, such as the Monterey Bay area, roses could show new growth of leaves and buds in the early winter for the same reason: an unusual warm spell. The National Weather Service, reports that the Monterey Bay area is having such a warm spell this year: November’s average high temperature was about five degrees above the historical level. When the NWS reports December’s data, we might well see the same pattern.
In such cases, gardeners need to either let their roses develop such new growth, or proceed with seasonal pruning. Here are three issues.
First, the new growth might not survive the winter cold. If that happens, the plant will have wasted energy producing the new growth, but suffered no lasting harm. A rose has two inactive dormant buds at the base of each leaf that can activate to grow new canes or leaves.
Second, if the new growth survives, the rose will miss its opportunity to rejuvenate. This could have long-term negative effects on the rose’s life and blossom production.
Finally, a break from dormancy means that the plant is sending fluids into the stems, making it vulnerable to a freeze that would expand the fluids and cause splits and tissue damage.
The preferred response to a broken or delayed dormancy, then, is to help the rose to enter dormancy. The gardener can do this by removing all leaves from the plant. This action will halt photosynthesis and encourage dormancy.
Once the plant becomes dormant, the gardener could accomplish seasonal pruning during the dormant period, which will continue to the early spring, after the last date when frost is expected.
Scientists are virtually unanimous in agreement that human-produced carbon dioxide emissions are causing global climate warming. This change is having countless effects, and including new issues for gardeners.
Fortunately, roses are tougher than they appear.
As part of my research into rose dormancy, I visited the website of the American Rose Society, which has great information on many aspects of rose growing. I didn’t see discussion of the late-season new growth growth issue, so I clicked on the link, “Ask a Question About Growing Roses,” and asked my questions.
I received a quick response from AIS Master Rosarian Karl Bapst, a self-described “Rosenut.” His own website http://www.rosenut.com/ has a wealth of rose-growing information that I expect to visit often in the future.
I even quoted Karl (without attribution!) for the closing line of my column.
Rather than trying to summarize his detailed information, I am including our e-mail dialog below, with minor editing.
Roses in this area (USDA Zone 9a) should be dormant now (mid-December). Some people have started winter pruning, only to discover that their roses have new leaves, due to an unusual warm spell (possibly global warming) in November. This new growth probably won’t survive the colder weather in January, but what harm might be done to the plant by pruning when new growth is showing? Also, what harm might cold weather cause to a rose with spring-like new growth in December?
In your area, I doubt your winter temps will drop down far enough to damage any new growth. New growth has lots of sugar that acts as natural antifreeze. In my area, zone 5a, mid-spring temps can drop to the mid to low 20s and new spring growth is seldom affected. If it is affected, new growth occurs to replace it. Keep in mind there are two inactive dormant buds at the base of each leaf. If that new leaf should die, one or both of the buds activate growing new canes or leaves. So, should any new growth be damaged by temps below the mid 20s, it’ll soon be replaced.
We often have new growth before we prune in spring. The rose bushes do just fine. I’ve pruned as late as late April and early May (due to inclement weather or illness) after the bushes are leafed out with no bad results. The roses even bloom at their normal times.
Roses are tougher than they appear.
I have sent in my column today with recommendations based on your advice, but I have a follow-up question. Last night, a Consulting Rosarian recommended responding to this new growth by defoliating the plant to encourage dormancy and completing seasonal pruning. (Most people around here prune between mid-December and mid-January.)
In warmer growing zones where there may not be natural dormancy, removing the leaves will promote a period of dormancy when the daylight shortens and temperatures moderate as we approach the winter solstice. Roses don’t naturally go dormant and will grow all year if conditions are right.
Modern roses bloom best on new wood, pruning promotes new wood so one gets more and bigger blooms. In my zone 5, winter’s cold and gloomy overcast skies, freeze and kill the leaves. Most stay on the bush until new growth or pruning removes them. The frozen soil and canes causes all growth to stop until conditions improve in late winter or early spring. Summer cutting of roses is pruning. You’ve noticed that cutting a bloom in summer causes a new cane to develop, usually from the base of the leaf under the cut. This occurs after your December/January pruning but on a larger scale.
Should you fail to prune or cut back then, any blooms produced on the un-pruned bush will normally be smaller and fewer on shorter canes. You’ll notice, though, any blooms will come from those short new growth canes. Even blooms that grow from the old cane tips will be on new growth.
In my area, we have no choice. When removing winter die-back or damaged canes, we force new cane growth. Often, especially on hybrid teas, which are naturally very winter-tender, removing die-back requires pruning almost to the ground. These bushes will bloom in late May/early June and will have grown to full size by July.
Understand, Old Garden Roses (OGRs, once-a-year blooming roses) bloom on old wood and buds are set the previous fall. Pruning on OGRs is done after they bloom or these buds would be removed when pruning. Should you get any questions from people asking why their roses don’t bloom it’s usually due to them pruning too early on Old Garden Roses.
I read a variety of online material in preparing this column, and found various pieces of relevant information.
For example, here’s an interesting point for the eHow.com website:
“Most rose plants that are capable of dormancy will not naturally initiate this process in response to cold weather. Most rose plants which are domestically grown in North America are hybrids with breeds of plants that evolved in Asia (most roses are Asian and are crossbred for their desirable characteristics, such as smell and appearance). Asian winters are not as harsh and, thus, dormancy in Asian roses is an evolved response to a lack of light. This can create problems for such roses in North America, where a cold winter can still supply enough sunlight to encourage the plant to keep growing.”
Such subtleties can be challenging for a garden writer with a deadline, and impossible to explore in a single column. I made no effort to explain the role of winter light in promoting or discouraging dormancy.