The middle of April is the best time to prune and first-fertilize roses in my experience. All dead leaves should be removed from the canes and base of the rose. These leaves often carry diseases that have over-wintered from the previous season. A diagonal cut should be made into each living cane, taking no more than a third of the cane. Dead canes should be removed entirely. A very sharp pair of pruning clippers is critical to this procedure. Because one of the most destructive insects to prey on the rose in many areas is the carpenter or burrowing insect, the end of the pruned cane should be immediately sealed with a rose or glue stick.
Other destructive fungal diseases and insects are powdery mildew and thrips. I have tried various three-in-one feeds with fungicide and insecticide added. I am unimpressed with the results. I know that organic gardening is something of a religion these days, however it has been my experience of some 40 years that a stubborn insistence upon organic gardening in the face of a blight-like infestation can cost you a vegetable, rose and/or perennial season.
Two years ago I lost a number of blooms on a magnificent rose to thrips (Neptune featured above). Cutting back the tender buds and blooms where the thrips feed on an infected rose is part of the recommended treatment. Only a rose lover can understand how heartbreaking it is to have to prematurely cut back the young buds on a lovely rose in the hope of stemming the spread of these nasty little attackers. Had I worked strictly organically - which might well have allowed the thrip to run its course - I could have been forced to remove several groups of buds and might not have seen another prolific bloom period that season.
Colorado high summer brings temperatures in the high 90’s to low triple digits. No doubt to protect her fragile, satiny petals the rose prefers to bloom in early to mid summer’s cooler temperatures on the Plains. My decision to prune back the larger buds in addition to administering a single bi-weekly dose of Rose Pride killed the thrips and quickly. A hardy rose like Neptune will continue to push growth and buds as long as the temperature stays mild to spite the over pruning.
Deciding which chemicals to use including fertilize, if you are going to use chemicals, requires thought and research. Out here on the High Plains roses are susceptible to virulent insects like the aphid and the spider mite, as well as the burrowing insect and the thrip. They are also highly susceptible to the destructive fungi red spot and black spot in addition to powdery mildew. If your roses are also inclined toward vulnerability I would suggest that you consider the short term use of insect, disease, and plant specific preparations for the treatment of roses and other plants in your garden.
I am not trying to make an either/or argument here. Organic gardening is wonderfully effective until it isn’t.
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