Forsythia signal trim time

Q. I’ve heard the rose should be pruned back in spring. If so, when in spring should I cut them back?

Brian from Boardman

A. If you have re-blooming roses, a good indicator on when to prune them in the spring is when the forsythia begins to bloom. The bright yellow flowers are a sign for spring and a sign for spring work!

But what if you don’t have any forsythia around? You can then use Growing Degree Days (GDD) to find the right time to prune your roses. What are GDDs? GDD is a measure of heat accumulation for a growing season and is expressed as a number that increases as the season progresses.

Plants and insects don’t care about the date on the calendar. They pay attention to the increasing average temperature to know it’s time to emerge.

The growth and development of plants (and insects) is influenced by temperature. GDD tracks the buildup of heat to predict when events will begin to happen. For the earliest forsythia blooms, the GDD value needs to reach 58. This year, we’re already ahead of that GDD value. But our typical forsythia bloom at 116 GDD, a level most likely to be reached sometime this week.

How do you know what the GDD of your location is? One of our OSU Extension websites will tell you the GDD for your area based on your zip code. Go to this web address – http://go.osu.edu/phenology – to find the calendar and even more details on phenology. You’ll be able to tell when everything from the emerald ash borer (EAB) to Japanese beetles will emerge to feast on your most beautiful plants.

When the website comes up, type in your zip code, and the website will show what the GDD is for that location. The website does not allow for local variations in climate called microclimates, so the GDD for your yard may be a little ahead or behind the website. That said, if you don’t have any forsythia around, the GDD information will give a good idea on when it’s time to prune the roses.

Also when pruning roses, be sure to use a clean, sharp pruner and make cuts at a 45-degree angle about º- inch above a bud. Cut out any canes with winter damage, dead areas or canes that look diseased. For more information on pruning roses see: http://go.osu.edu/pruningtheroses.

Today’s answer is provided by David Sprague, OSU Extension master gardener volunteer. Call the office hotline at 330-533-5538 to submit your questions. Regular clinic hours begin April 4, on Mondays and Wednesdays from 9 a.m.-noon.