Question
QUESTION: I have a rock wall at our new home site.  The landscaper put in azaleas and other evergreens.  I put some knockout roses in for color, which did well.  I am thinking of putting the knockout ground cover rose in so that I will have color hanging over the rock.  The beds contain a good amount of yazoo clay.  Do you think these would do well as the beds get full afternoon sun?

ANSWER: Hi Frank,
Thanx for your question.  Can you give me your general location?  Central Mississippi?  Do you know what variety of rose ground cover you are wanting to use?  The ground cover roses do well up here in Kansas and we have some clay soils around the Kansas City area.  I have noted ground cover roses doing well on the East Coast.  You can amend the clay with composted cow manure and keep working it into the soil every year to improve tilth (soil condition) and organic levels.  The roses do best in full sun even though it gets hot and humid in Mississippi.  What you want to do is look for rose varieties that are low in susceptibility to black spot and other fungal diseases or you will have discolored and unsightly leaves.  Let me know and I'll see what else I can find for you.
Tom

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QUESTION: Brandon is in Rankin County, just across the Pearl River from the City of Jackson.  When I put the knockout roses in last year I researched them on the web and I there they mentioned the ground rose in the knockout family, but did not give any other information on them as to height and width that they would grow or if they would give me the trailing over the rock wall I want to get.  I did try wave petunias last year and put out 18 plants and none of them made it.  I hope this gives you more information as to what I am attempting to do.  Thanks, Frank

Answer
Hi Frank,
Thanx for the additional information.  I know your area well.  I used to go through there all the time when I was commuting between NW Florida and Kansas City.  The trouble with roses flowing over walls is that the plant auxins (growth hormones) start to kill growth on the lower ends of the growing tips.  The auxins are always going Upwards to increase upward growth so starting to trail down the auxins will perform conversely.  Seriously Frank, I'm not really a rose expert and I shouldn't be talking like I am but this is the information I was able to glean about trailing roses.  The knockout roses are actually a compact, low-growing, ground cover form of rose that usually maintain a 3'X3' compact growth habit.  If you want something to trail over the rock wall, you could try rosmarinus (rosemary) which has some wonderful trailing types with cool foliage that will bloom in purples, whites and I think even a blue plus they have a pleasant scent and they're perennial in your zone.  They are drought tolerant and grow well in rocks.  By the way, your knockout roses are blackspot resistent which is good for the humid South.  You could also look into trailing roses (I think the antiques are the best and offer heady scents) that are rated for the Deep South (your local nurseries should have them) and train them along the wall.  I'm sorry I don't have better information for you.  You mentioned petunias which are actually an annual but there are annuals that would work trailing over the wall too.  You could invest in some bougainvillea.  It would trail over the wall but your would have to keep it in pots.  MSU says that in all but the Gulf Coast of Mississippi, bougainvillea must be treated as an annual but it is usually fairly inexpensive (even up here) and makes a great, colorful flow over walls.  Something you might want to look into.  If you have greenhouse space available, you can keep the plants in pots and bring them indoors in November.  I hope this helps.
Tom