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Right now my knockout roses are out of control and need a good trim, but it's freezing here in Kentucky. For some reason this cold weather we're having here isn't preventing them from growing~!
I am new to the art of growing roses (my Dad grew them and I'm now trying to figure it out). It's my responsibility to maintain a rose garden I helped install here where I work (UNC-Charlotte Botanical Gardens) and am becoming frustrated beyond belief trying to control black spot on the 12 +/- roses we've put in so far. What is the best way to avoid black spot getting established in the soil to begin with and how do you control it once it's there. I've tried keeping all of the mulch raked away from the affected roses, removing leaves on a weekly basis (both picking them off and picking them up), spraying and drenching the soil... I think I'm probably not spraying them often enough since I only work at that site once a week. Another question: to mulch or not to mulch and, if mulching, what type is best to use and when should it be replenished? As the weather has cooled off I've noticed more black spot showing up, even on the Knock-Out roses, not just the Old-Fashioned roses. Would it be advisable to remove all of the mulch after we have a hard frost/freeze (assuming we get one this year before spring returns), saturate the soil with a fungicide, followed by a dust of Sevin (does that work on black spot?) and leave the soil bare for a few weeks? Or should I replace all of the mulch after doing the soil saturation treatment and, if yes, how deep should the mulch be. Can you tell I'm getting frustrated? This was just the second year for having the roses in the ground and blooming and if there's a way to stave off a massive black spot infection of the entire garden, I really want to give it all the effort needed so the area keeps on looking good through the coming years.
We have a similar climate in summer so I sympathize with your worries. The Knockouts generally are the most resistant so it does sound like your gardens are harboring a lot of spores. With all the spraying and drenches you should have been able to get control of the problem even if you can never get it to go away in our humid summer climate. This winter may be the best chance you have to conquer it.
Start now by cutting away anything that still has any signs of infection and make sure every last leaf and twig is thrown out, no composting. As soon as the roses are fully dormant, and all other plants around them are dormant and cleaned up the same way, remove all the mulch around them, not just what is close by. The remaining spores for next year's infection will be in infected leaves and mulch so being really thorough makes a huge difference. Since winter weather is hard on plants in the mid south you will need fresh mulch for the warm to freezing cold cycles. If you cannot get fresh clean mulch by mid December then postpone replacement until late February when there should be fresh stock available again. Be thorough about cleaning up the old materials -whenever!
To reduce the infection rate use a multi care product that includes an antifungal. Bayer's 3 in 1 for roses is one example. Some people swear by the drenches but I've found the granular mixed into and beneath the mulch works well for me when just spraying and more organic methods have no worked as well. Follow the directions and do not use additional fertilizer.
You will need to do an aggressive pruning. A Knockout will be more susceptible if there is not enough "air" circulation and many other rose varieties have similar needs. Makes sure you follow pruning schedules for each type. The Knockout needs mostly cutting back and shaping but if it is older it may also need the oldest and largest canes cut back to the base to allow new healthier growth to take over. The best time to prune it is the same week you begin to see forsythia beginning to open up.
As the roses begin to grow make sure any watering is done is at the base of the roses and not from above. Damp and wet leaves make new breeding grounds for new mold from any remaining spores. Watch for signs of disease as soon as we get the first really warm and humid days. If you use only one type of fungicide you may also run into difficulty as the year progresses. You will need to alternate treatments and treat every 7 to 10 days in the hottest and most humid days of summer. I like to use at east some organic methods for this, such as a baking soda-horticultural oil spray and a dilute vinegar spray. To save money and keep sprays in a rotation try one of the following "recipes" for the organic weeks and use commercial products from Safer or Bonide and reapply the 3in1 as directed. If you still get more spots escalate to more potent products and use with care.
Roses grow like weeds where I live, in a very hot dry climate.
There are lots of rose farms about and they just prune them with a chainsaw...straight over the top. They don't get mulched at all, some of the bushes are over 100 years old and still going strong.
Too many people fart around with roses, you actually can't kill them unless you overwater. They are one of the hardiest plants around.
I'd spray them for black spot, prune the hell out of them (they love it) and leave them alone otherwise.
I suspect the black spot spread is due to dampness and too much mulch.
And knock-outs are even more tolerant of just about anything! I only have one rosebush that I do the prune on Valentines thing and that's only because it came with the house and I don't know anything about it. Knock-outs, I'll cut `em, dead head, whatever, whenever I feel like it. I don't think I could kill one even if I tried.
I've appreciated reading all of the info on how to control black spot and, while I'm resigned to having some of it on two of the roses no matter what, I loving the challenge of keeping it at bay on the two double-pink Knock-Out roses that have taken a beating this summer. I think several things combined for the "perfect storm" of black spot attacking. First we had a fairly wet Spring/early Summer, followed by the usual stretch of hotter than normal weather, which came with the beginning of a very long dry stretch that's not over yet. Secondly, after reading the info from the University of Maine, it seems I need to keep the roses in the upper tier from getting so leggy. The two old-fashioned heritage roses get lanky as the summer goes on and we haven't kept them pruned back based on the suggestions of the grower they came from...I'll keep them more contained next growing season. From what I understand they should not be in such close proximity that the canes from the adjoining roses get tangled together. The third thing is that I do need to keep them mulched, not with the ground kept cleared off so it's easier to see the fallen leaves. The University of Maine site says mulch will keep the fungus spores from splashing so high. I re-mulched the other day, after spraying everything really well with Neem Oil and made sure I removed all of the old mulch and dead leaves as well.
***I'm also going to ask for soaker hoses so when I do need to water I'm not splashing water on the leaves.
****next question for people who grow roses in the Piedmont area of North Carolina (Charlotte area), what type of mulch do you use on a regular basis? we order two things in bulk: "bark fines" or pine mini-nuggets and pine bark nuggets that are larger by far. We get these types of mulch from a local landscape supplier, a dump truck load on a as-needed basis, two or three times a year. If a shredded mulch would be better I'd like to give it a try.
***on a personal note, I have a rose growing at my house that never gets black spot...never. I don't do anything to it...ever. well, I did cut it back in the Spring 2 years ago, but it's just as large as before. I dug it up from the side of a house slated for demolition, plopped it into the ground pretty much barerooted, watered it and left it to fend for itself. It took off like nobody's business. I've since learned that it's called Pink Parfait, a very disease resistant multiflora shrub type rose, developed in the late 1950's. It starts blooming in the early part of the usual bloom season and is still blooming, heavily, even though we had a good freeze. Go figure.
****thanks for all of the help
again, thanks for the feedback and I'll post from time to time how things are going.
I live in FL. I have a knockout rose garden red and white, which I didn't know you could buy white, they have a wonderful fragrance unlike the other colors. I have had knockouts at my old house they did wonderful until I pruned them now I am scared to prune the ones that I have now. I want to prune them about 12" but it has been very warm here so there is a ton of new growth. The weather has been so sporadic here I am scared if I cut them back and it gets cold it will kill them. Any ideas or knowledge regarding this will be wonderful.
I must have posted about my Knockouts awhile back, about how well they have done on the SE corner of my house, but I plan to cut mine way back in the spring, since they are looking a bit tired, despite regular feedings and fungicide. Although here in this zone 8 climate, they continue to bloom through most of the winter, they look a bit bedraggled. I think I will put a bag or two of Black Cow around them to enrich the soil, and also remove the fabric around them.
We have very old garden fabric in our front beds which I feel has kept the soil from being enriched, although it does a fair job of keeping weeds at bay, at this point there is a layer of compost on top of the fabric that is able to support a good crop of weeds anyway. I have had a chronic problem of flowers and shrubs that do very well for a few years, but then up and die. The southerners say plants die when the roots hit "the gumbo" which is clay, I think. I think the garden fabric/gumbo issue is to blame. Its worth a try at enriching the soil.
I pruned ours in October, and we are in Zone 7, Delmarva Peninsula. Knock Outs grow like weeds here, and are on every gas station corner, on casino grounds, and on shopping center islands. I prune them way down to a foot tall, and don't deadhead them all summer long. They take care of themselves.
I live in FL. I have a knockout rose garden red and white, which I didn't know you could buy white, they have a wonderful fragrance unlike the other colors. I have had knockouts at my old house they did wonderful until I pruned them now I am scared to prune the ones that I have now. I want to prune them about 12" but it has been very warm here so there is a ton of new growth. The weather has been so sporadic here I am scared if I cut them back and it gets cold it will kill them. Any ideas or knowledge regarding this will be wonderful.
Actually, I don't think the white one is a "knockout" (tm) rose. Do you have "white out?"
I live in FL. I have a knockout rose garden red and white, which I didn't know you could buy white, they have a wonderful fragrance unlike the other colors. I have had knockouts at my old house they did wonderful until I pruned them now I am scared to prune the ones that I have now. I want to prune them about 12" but it has been very warm here so there is a ton of new growth. The weather has been so sporadic here I am scared if I cut them back and it gets cold it will kill them. Any ideas or knowledge regarding this will be wonderful.
It probably is not a Knockout if it is white but may be related because the same grower that created the Knockouts also has one called the White Out. Knockout roses are pretty resilient but even they can be damaged if treated poorly. The original grower developed them for being more cold hardy so the chances are you won't kill them outright but any new growth pruning stimulates may be killed in a sudden freeze. If they are putting out new shoots now and your area has had strong freezes in January I would wait to the time the Florida cooperative extension says is safest. That would be close to the middle of February when any cold spells will not be enough to hurt the roses but growth is just starting to pick up. Twelve inches is a pretty severe pruning for Knockouts, unless you are trying to keep them under 3 feet high, and usually is not recommended to be done more often than eery other year. If you need to just neaten up scraggily growth you can prune it off now and any damage from cold to the new growth on that cane can still be trimmed later in a bigger pruning.
For answers from people who know your local conditions you can always contact the local extension office and ask to speak to a Master Gardener. Here's the complete list for Florida: Local Offices - UF/IFAS Extension: Solutions for Your Life
This is the advice of the company that owns the patent and is still developing new Knockouts:
Quote:
Prune your rose bush in early spring, never in the fall and never in the winter.
Sumter County FL Master Gardeners put out some great newsletters that discuss when to do things in Florida gardens. Unfortunately it is all pdfs that are hard to link to directly but you can find the one on Knockout Rose pruning and care on this list if you go to the February 2011 newsletter. Sumter County Gardeners Journal
Quote:
Originally Posted by gentlearts
I must have posted about my Knockouts awhile back, about how well they have done on the SE corner of my house, but I plan to cut mine way back in the spring, since they are looking a bit tired, despite regular feedings and fungicide. Although here in this zone 8 climate, they continue to bloom through most of the winter, they look a bit bedraggled. I think I will put a bag or two of Black Cow around them to enrich the soil, and also remove the fabric around them.
We have very old garden fabric in our front beds which I feel has kept the soil from being enriched, although it does a fair job of keeping weeds at bay, at this point there is a layer of compost on top of the fabric that is able to support a good crop of weeds anyway. I have had a chronic problem of flowers and shrubs that do very well for a few years, but then up and die. The southerners say plants die when the roots hit "the gumbo" which is clay, I think. I think the garden fabric/gumbo issue is to blame. Its worth a try at enriching the soil.
Gumbo is a form of clay, yes. A good friend and avid gardener in Louisiana tells me the only "cure" is amending, more amending, and raising any and all flower beds above it. The weed filled, compost covered fabric probably is not helping the roses. Your plan sounds like you are headed in the right direction to revitalize your roses. Good luck.
The white is kind of a cream color, more yellowish than white. But since I read the forum I pruned them all back now they are all covered in flowers, thank you!!!
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re: black spot
