Consulting Rosarian Tip of the Month – MAY

May CR Advice by Barbara Kemp, Master Rosarian

Our roses have been on a roller coaster with fluctuating temperatures. Some of my roses did not ride out the curves very well with the last two storms in April that brought inches of snow and freezing temperatures. We are all looking forward to warm May temperatures and to beautiful rose gardens again!


We begin seasonal rose pruning the end of April to mid-May pruning out old dead canes, thinning out the center (if needed) to allow more air flow, and ensuring that there are no branches crossing or rubbing on others causing damage. Many roses may have “hard pruning” cutting out black dead canes to ground level, so be sure to seal cane cuts with waterproof glue. (Try Titebond waterproof wood glue; it’s great!) Clean around rose beds and dispose of debris and diseased rose canes in the trash; do not compost.


Planting Container Roses: You can begin planting container roses when there is no danger of freezing temperatures, which is around May 15 for the Denver metro area. After purchase, container roses will need to be hardened off for a few days in an outside covered area to become acclimated to outdoor temperatures as these roses are grown in a greenhouse environment. When choosing your site remember that a rose needs at least six hours of sun. Dig the hole approximately 18 to 24 inches wide and 14 to 18 inches deep. To ensure that the planting depth is correct, place the container rose into the hole and use a pole or shovel handle to determine the depth: the branching point of an own root rose is planted approximately two inches below ground level; grafted roses are two to four inches below ground level. When planting container roses, remove the rose from the pot; do not plant a rose in the container even if the container is made of some type of compressed material as it will not decompose in our climate and it would compromise the growth and watering of the rose. Cut out the bottom of the pot and slit the sides to assist sliding the root ball into the hole. Try to keep as much of the root ball together as possible. If the root ball crumbles, plant as a bare root rose as described in a previous newsletter issue. If the rose is root-bound in the pot, work the roots loose on sides and bottom with your hands before sliding and spreading roots into the soil, then water. If the container rose did not receive fertilizer, you may add a small amount of our organic Mile-Hi Rose Feed. It is recommended to water new roses daily for several days, then twice a week, and then once a week until you begin your watering cycle.


Watering: May will begin with high 70 to 80 degree temperatures, so plan a water schedule and increase it to twice a week throughout the summer, always checking soil moisture as you go. A good soaking rain will allow you to skip a cycle of irrigation. Water during early mornings to allow time for wet rose leaves to dry off. Don’t forget to water roses more often during hot weather. To help retain moisture levels on hot days, apply generous amounts of mulch around the base of the rose to keep soil temperatures even and cool.


Fertilizing: We also start our fertilizing cycle in May with two more feedings around the first week of July and in late August. The Denver Rose Society highly recommends using organic fertilizers (Mile-Hi Rose Feed, kelp, and alfalfa meal) that produce strong healthy canes, good foliage, and beautiful blooms. Remember to water roses before and after fertilizing at each feeding.

You will soon get to know the pests and the beneficial predators in your garden by monitoring rose beds daily. Following good horticultural practices and identifying pests early, you may only need to control aphids with water sprays or use fingertips to remove other pests. Refer to Growing Roses in Colorado for pest descriptions, symptoms and suggested controls.
These May tasks should start roses thriving and get them ready for a rose show this summer. Enjoy your time in the garden as roses begin to grow from your May pruning, fertilizing and watering.