When a gardener has grown the perfect rose garden, they don't want to use trial and error to reproduce their efforts. Since selection, availability and quality, are unknown variables, the last thing a gardener wants to do is hope they can get the same type of plants to perform the same the next growoing season. Roses are mainly plants that survive in temperate climates that demand a lot of attention and with the exception of a few hardy hybrids, can not survive the harsh winters of the Red River Valley. At the end of the growing season, there are steps the gardener should take to have successful results year after year.
Timing and planning for the winter season is a very important factor for winterizing roses. After deciding which method, the gardener needs to make sure they have the necessary equipment. In the late fall period, the roses should be fertilized with a supplement that does not have nitrogen. This will help prevent any additional growth when the plant should be preparing for the dormant season. It is also important that the plants be checked for any disease or infestation and properly treated prior to winterizing. Early detection and treatment will make the plant less susceptible to winter injury. The next step should take place after the first frost, but before a deep frost sets in. This involves prunig the rose bush back. The length of the remaining canes depends on the method of witnerizing.
There are three common methods to insure that the plants from this years garden are available for the next year. Each has some labor involved and there are other factors such as space and equipment that should be considered. The first method that has a lot of drawbacks involves digging up each bush, potting them and storing inside for the winter. Pruning for this method is recommended to save space and give the plant some dormancy. This involves a lot of pots, as well as storage space. Other problems include damaging the plant's roots and not allowing the roses to build up any tolerance to climatic conditions which can be an expensive venture. The plants must stay warm through the winter and should not be moved back to the garden until the temperature is sure not to fall near the freezing level.
The next two methods are more commonly practiced in this region. The mound method involves wintering the plant in the garden. The first step (insuring the fertilizing and inspection has been accomplished), involves cutting back the canes to 12- 18 inches. Then the gardener should bring in (from another location) lean, sandy soil. Build this up around the base of the plant 8-10 inches high. The soil should be loightly compacted to keep the pruned canes firmly packed.
The next step involves using either chicken-wire or a cage to place mulch around and over the rose canes. The mulch can be any type, such as pine needles, straw, bark, or leaves. The mulch provides additional protection for the rosebush from fluctuating temperatures. Some gardeners use styrofoam cones but these can build up heat inside which could prematurely start the plant out of dormancy. If the cones are used it is recommended that the gardener punch at least one hole to prevent heat build-up.
In April it should be save to bring the roses back from dormancy. When
the weather has started to warm, the mulch should be removed and the dirt
carefully pulled away from the plant. This should be followed by a quick
inspection and removal of any dead branches. The gardener should water
the roses well and the plants should be ready to go.
The last method that is used in this zone is the tip method. The tip method requires the gardener to dig a trench about a foot deep, near the root system. Using this method, the canes need to be cut back to no more than 2 feet. Some gardeners prefer to tie the canes and this should be done with a material or rope that will not cut the canes. Some like to leave a little extra cloth on one end laying above ground, to help locate the plant in spring.
After the trench has been dug, the roots need to be loosened, and the
plant leaned over on it's side in the trench. The plant then needs to be
covered using the soil and then mulch piled over the rose. One significant
problem with this method is the likelihood of damage to the plant or root
system.
When spring arrives the mulch should be removed as it thaws. After the danger of frost is over, the plant should have the dirt removed and stood back up. The binding material should be removed and the plant watered thoroughly.
NDSU Extension Service- www.ext.nodak.edu/extnews/askext/flowers/1213.htm
University of Minnesota - www.extension.umn.edu/info-u/plants/BG434.html