Horticulture professor Allen Owings leads a rose care discussion in the sun garden at the LSU AgCenter Hammond Research Station. (Photo by Johnny Morgan, LSU AgCenter)

Sweet Drift is a popular low-maintenance shrub rose for Louisiana. (Photo by Allen Owings, LSU AgCenter)

News Release Distributed 07/10/15

By Allen Owings
LSU AgCenter horticulturist

HAMMOND, La. – Summer is not the most enjoyable time to work in the yard in Louisiana, but rose bushes need attention to ensure good performance through the summer and into early fall.

The popular varieties of Knock Out and Drift roses are the ones most planted these days in commercial and residential landscapes around the state. Many home gardeners also still grow hybrid tea, floribunda and grandiflora roses and we still see considerable interest in old garden varieties.

During summer, you will notice the flower colors are less intense and the blooms are smaller. These conditions are simply the effects of the summer heat. Improved flower color and flower size will resume this fall.

Roses need disease management from July through the end of summer for good flowering and performance into fall. Irrigation also needs to be maintained during drought-like periods. Typically, roses need 3/4 to 1 inch of irrigation weekly in summer when rainfall is lacking.

Do not prune roses now other than to take off old flowers as they fade. “Deadheading” in these months means less pruning later.

We recommend late-summer pruning of modern rose varieties such as hybrid tea, floribunda, grandiflora and shrub roses. Anytime from late August to early September is the statewide recommended time to prune. Pruning then should be less severe than pruning typically done in February. Blooms return to late-summer-pruned roses in 35-45 days, depending on the variety.

Here are some other rose care recommendations for summer:

– Watch roses for insects and mites. Spider mites, aphids, flower thrips, chilli thrips and cucumber beetles usually are the main problem insects on roses. Some insects can be easily controlled; 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 Preen or Amaze pre-emergence herbicide for summer weed control. Be careful with post-emergent herbicide application around roses. It is easy to damage roses with some herbicides.

– Add new mulch if you did not refresh the bed earlier in the year – pine straw is an excellent material. Even if you did add mulch earlier, a new application on top of the older mulch may be beneficial. Three inches of pine straw is ideal.

– Continue a preventive fungicide spray program for blackspot control. Treatment depends greatly on the kind of roses you have, because roses have varying degrees of blackspot susceptibility. Spray on a 10- to 14-day schedule on susceptible varieties.

– Spread a light application of a slow-release fertilizer when pruning is completed in late summer. You can also apply Epsom salt to roses at that time to encourage greener foliage and enhance basal branching. It would be a good idea this fall to take a soil test to check the soil pH in your rose garden.

You can see more about work being done in landscape horticulture by visiting the LSU AgCenter Hammond Research Station website. Also, like us on Facebook. You can find an abundance of landscape information for both home gardeners and industry professionals at both sites.

Rick Bogren