News Release Distributed 05/28/10
By LSU AgCenter Horticulturists Dan Gill and Allen Owings
Spring rose bloom was outstanding this year. The cooler weather through the winter did very little cold damage, and the dry weather and cool nights in spring led to a tremendous peak bloom throughout the state in mid- to late April.
We are now rapidly approaching the summer months, and rose bushes will not necessarily look their best. This is especially true in July and August.
These days, many gardeners are planting an abundance of landscape or shrub roses, including the popular Knock Out varieties. Nevertheless, other Louisiana home gardeners enjoy growing the traditional hybrid tea, floribunda and grandiflora rose varieties.
During the summer, flower colors are less intense and blooms are smaller, and petal counts will decrease. For instance, a Knock Out rose with 10-12 petals in mid-spring may only have five to six petals in late summer. You also can see petal counts reduced on hybrid tea roses. They typically have 40-50 petals per flower, but petal numbers are not as high in the summer – and flower size is smaller. Also, flower pigmentation is not as good because of high temperatures and unfavorable growing conditions.
Roses need disease management and possibly fertilization from now through the end of summer for good flowering and performance into the fall. Normally, the varieties with high to moderate susceptibility to blackspot disease need to be sprayed with fungicide on a 10-14 day schedule. But you may see foliage burn because of fungicide application during the summer.
Fertilizer probably should not be applied during the middle of the summer, but a light application in late May through mid-June may be of value. Irrigation also needs to be maintained during droughty periods. Apply water to the mulch and the root zone area around the plants.
Do not prune roses in June and July other than taking off old flowers as they fade. If you continually “deadhead” roses during the summer, you’ll need less pruning later. The recommended late-summer pruning of modern hybrid tea, floribunda, grandiflora and shrub rose varieties should be completed by early September in south Louisiana. Blooms will return on the pruned bushes 40-45 days after pruning.
Other rose-gardening work that needs to be done through the summer months includes:
– Watch roses for insect pests. Spider mites, aphids, thrips and cucumber beetles are usually the main problem insects on roses. Some can be controlled easily; some are more difficult to control. Monitor your plants weekly for insect infestations.
– Clear debris from rose beds and pull any weeds that may be present. Add pre-emergent granular herbicide for summer weed control.
– Add new mulch if you didn’t refresh the bed earlier in the year. Pine straw is an excellent material. Even if you did add mulch earlier in the season, a new application on top of the older mulch may be beneficial. Three inches of pine straw is ideal.
Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.louisianahouse.org and www.lsuagcenter.com/lyn.
Rick Bogren