5 on Your Side

My Knock Outs aren't so "knock-out" anymore!

Posted June 1, 2010

I LOVE to work in the yard. O-K.. I LOVE it depending on the task. For example, I like to TRIM bushes-- but I don't like to actually PICK-UP the trimmings! I like to PLANT flowers, but I don't like to CLEAN UP the dirt left all over the deck when I'm done! Thank goodness my husband is always willing to pick up after me!

Anyway-- some of my favorite additions to my yard in recent years are my Knock Out roses. They've been a dream for a do-it-yourself landscaper like me who sometimes has a thumb that's a little more lime colored than dark green! That's been until the last couple of weeks-- when they suddenly stopped blooming! I've been pondering the problem until Gary Pierce, a Horticulture Extension Agent in Harnett County-- came to the rescue with the following e-mail! And I encourage anyone who likes gardening to get on his "list." His "Ask the Hort Agent" e-mails are always informative and entertaining!

Ask the Hort Agent

Why have my Knock Out Roses Stopped Blooming?

Before you throw in the white towel, give the plant a standing 10 count. The 'Knock out' Rose is a group of hybrid shrub roses bred to require less maintenance with greater disease resistance and cold tolerance. In 2000, the original Knock Out Red was introduced and won the All American Rose Selection Award. Since this time, Knock Outs have become best sellers.

These roses usually bloom like a house on fire the first and second year. Sometime between years 3 and 5 they get so big they can run out of resources to keep them blooming. Roses need 3 things to bloom: sun, water and fertilizer.

Most roses need 8 to 10 hours of sun every day. Knock Outs can thrive on half that. This is a mixed blessing. Some people interpret this characteristic as a shade plant. Knock Outs are still sun plants. They do best in the sun. Less sun equals less blooms. Extended cloudy weather is also not conducive for flowering.

Give roses a minimum of 1 inch of water per week, and keep it off the foliage. Make sure your soil is well drained. They don’t like to stand in water.

Sometimes low potassium can contribute to blooming issues. High phosphorus rates encourage flowering and a strong root system. Differences in soil consistency may account for differences in plant responses to equal fertilization. Take soil samples to make sure your nutrient levels are appropriate in all flower beds. Slow-release fertilizers and/or compost offer a continuous supply of nutrients. Knock Outs continue to produce new flowers throughout the summer, but a little extra fertilizer may produce even more roses.

If you are supplying these things, try pruning them back about 10-20 percent. You can prune any time of year. Another characteristic bred into this rose was the ability to drop off its dead blossoms. In other words, Knock Outs don’t have to be deadheaded. While not needing to deadhead roses is a good quality, it can also slow down the ability of the rose to bloom again quickly. If you want to keep your Knock Outs blooming as often as possible, snip off the old blooms. Even though they will eventually drop their dead blossoms, you can get ahead of the game by helping them out.

For more info about Knock Out roses, visit http://gardeningsolutions.ifas.ufl.edu/giam/plants_and_grasses/flowering_plants/knockout.html For more information about pruning Knock Outs, visit http://www.ehow.com/way_5782600_do-need-prune-knockout-roses_.html If you don’t have internet access, call the Extension Office at 893-7533 or email me at gpierce@harnett.org

When I hear knockout, I think UFC (mixed martial arts). I visualize Chuck “The Iceman” Liddell in my yard pounding on my rose bushes. When he gets through with them, I won’t have to worry about blooms ever again. http://en.wikipedia.org/wiki/Chuck_Liddell

Gary L. Pierce
Horticulture Extension Agent
Harnett County



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  • IBleedRedandWhite Jun 1, 2010

    I use this Bayer Rose fertilizer stuff. Comes in a blue bottle with a measuring cup cap. Follow the instructions and within two weeks of putting it around the root system my bushes are full of blooms again! They say don't apply any after around July 31 to give the new growth time to mature and get ready for the cold weather.

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