Fertilize to boost the blooms of roses, azaleas

"With what and when do I fertilize roses and azaleas? Can I use the same fertilizer for both plants?"

These are common questions asked by gardeners quite often, especially in the spring.

Azaleas, rhododendrons

I will start with azaleas (rhododendrons are included with azaleas). My suggestion is to start fertilizing them in the spring after they bloom. It may just be my imagination, but I think azaleas should be allowed to open their blossoms in the spring based on ambient temperature. I don't want to force them to bloom by feeding them with fertilizer too early.

After they bloom, then begin feeding them on a monthly basis through August. You want to make sure that there are plenty of nutrients in the soil so that they can grow during the summer and then set bloom buds in the fall for a great show the following spring.

Because azaleas prefer acidic soils, purchase an azalea food that helps keep the soil pH very acidic. These fertilizers have higher concentrations of ammoniacal nitrogen than fertilizers for vegetables and most flowers.

Azaleas in the Heartland are often infested with lacebugs. These insects suck juices out of leaves and give the leaves a white/gray appearance. I suggest that you purchase an azalea fertilizer than has a systemic insecticide in it to help combat any lacebug infestation.

Roses

Roses should be treated slightly differently. Fertilize them right as they are beginning to bloom, or just as the flower buds are beginning to form. Roses bloom on this year's wood, so as the buds begin to swell you want to give them a nutritional boost.

Continue to fertilize roses monthly throughout the growing season until the end of August. This will encourage them to continue blooming throughout the summer. Quit fertilizing at the end of August because you want them to naturally slow down their growth rate before winter sets in.

When fertilizing, purchase a fertilizer specifically designed for roses. The source of nitrogen is different for roses than azaleas, because you don't want to acidify the soil. Roses like a more neutral pH.

In the Heartland roses are subject to insect infestations such as worms in the spring (particularly a problem this spring) and Japanese beetles in the summer. Therefore use a fertilizer that contains a systemic insecticide to help combat these insect problems.

You may find slow release fertilizers on the market for roses and azaleas. I tend to stay away from these fertilizers. Some release based upon temperature and others based upon soil moisture.

Because the climatic conditions are so variable in the Heartland, I think it is important that the gardener control when fertilizers are to be applied instead of assuming a slow release fertilizer will automatically release at the right time and in the right amount. Automatic fertilization is not always the best.

Treat your roses and azaleas with some TLC by fertilizing them at the right time and with the right fertilizers. They will reward you by blooming their hearts out.