Expert: Lynnette Callan - 11/2/2009

Question
QUESTION: I have a winter home in central Florida.  While gone this summer my knock out roses got out of control and also have discolored leaves.
When can I trim them back and how far?  What do I do about the discolored leaves?

Thanks.5

ANSWER: You can cut your roses back now. If you want them to be 3 feet tall then you have to cut them back to 18 inches as they will grow back again and become 3 feet tall. If you want them taller then only prune back to about 2 feet tall. If you are finding that the roses really go wild, then prune them right back to 12 inches and that should make a tidy bush for you.
I am confused about the leaves as rose leaves can have many problems which will cause different colours on the leaves. Can you describe the leaves for me please.

---------- FOLLOW-UP ----------

QUESTION: Some of the leaves have turned yellow and some have black spots.

Thanks, Glenda

Answer
Yellow leaves which have black spots on them, are caused by a fungal disease called Black Spot. This disease is usually worst in areas that get humid weather with warm temperatures. Knock Out roses are not free from the problem  and will need to be sprayed to keep the fungal spores under control. You can't cure the disease as the spores float around in the air and when they drop down onto a rose leaf they start their life cycle. Any rose spray for black spot on roses will help keep it under control. The only problem is that you have to us the spray regularly in your area if you are going to keep the roses clean. Here is the website of the rose society for your area and have lots of information regarding the problems of growing roses in your area plus answers to the problems.
http://www.centralfloridarosesociety.org/info/index.asp