It has been an exciting rose season this year in Flagstaff. One of our nurseries moved across town. They and the other nurseries in Flagstaff have given us an excellent selection of roses to choose from. Our new and well-established roses will slowly become dormant for the winter as the frosts and then the freezes (27 degrees and lower) progress. Flagstaff is within the USDA Zone 5 of cold hardiness, which means that the vast majority of our roses need to be mulched to be protected from the soil around them thawing and then heaving, which severely damages their roots.
Before you mulch tidy the ground around each rose. Prune off very tall, gangly growth that will be caught by the wind. Prune off twiggy top growth, less than 1/8 inch in diameter, which will also catch the wind. Here at 7,000 feet be very conservative pruning this spindly growth. Prune after the first freeze when the rose has had a chance to take its sap and nutrients back down the canes into the roots. Remove all dead leaves, and rake all leaf debris from under the rose and throw away. Do not put these in the compost as they could harbor insect eggs and plant diseases. Most importantly, make sure that the crown or bud union of the rose is still covered with two inches of soil. Add soil over the entire root zone to keep moisture from running off.
The best mulch is 6-8 inches of red cedar wood chips. The red cedar repels insects. The wood chips retain moisture, then release it slowly. They compact enough to protect, but not so firmly as to smother. First, rake your old cedar garden mulch under your roses. Then add new cedar chips to the depth of 6-8 inches. Fresh tree mulch pulls Nitrogen from the soil as it starts to decompose. The old cedar mulch will be a buffer, saving that Nitrogen to get spring growth started. However, do use new mulch rather than no mulch at all.
The second best mulch is 6-8 inches of pine needles. Make sure the center of the rose is deeply covered. The third best mulch is 8 inches of leaves, except for large leaves that compact too much. Be sure to encircle the rose with a cylinder of chicken wire to keep the leaves in place.
About mid-May when your rose leaves are starting to unfurl, drag away several inches of the mulch, leaving about five inches. Sunlight encourages growth. When the danger of frost has passed, around the first week of June, pull away the mulch, leaving three inches to hold moisture and to help average out the difference between day and nighttime temperatures.
When you make mulching in the fall as much a part of your rose care as watering and fertilizing, you are helping the rose’s root system establish itself in the ground. This takes several years. The better you are mulching, the less winter dieback you will have of the canes. The more healthy, long canes you have, the faster your rose will restart growing in the spring, helping it become larger in the coming fall than it was in the spring. Rose bushes that have not had the chance to increase in size are prey for severe deer browsing, further setting them back. The average lifespan of a rose is a generation, 20-25 years. Some live longer. Ensure that your roses will be among those robust ones by faithfully mulching in the fall.