Double knockout yellow roses

Yellow Knock Out Rose Leaves: What Makes Rose Leaves Turn Yellow

The yellowing of what should be healthy and nice green leaves on any plant may be a sign that something is not right. The yellowing of the leaves on a Knock Out rose bush can be one of the ways of telling us something is not right with its health and well-being. It can also be a normal occurrence that is part of the cycle of life for the bush. We need to check things out to determine which signal the rose is sending us.

What Makes Rose Leaves Turn Yellow?

There are a number of things that can lead to Knock Out rose leaves turning yellow. Some of these include the following:

Irrigation issues

One of the first things to check when noticing yellow Knock Out rose leaves is the soil’s moisture. Perhaps, it has been raining for several days or even off and on with misty or foggy conditions for multiple days. The lack of good sunshine and lots of water can indeed spell trouble. The rainwater saturates the soil, not allowing oxygen to move through and causing water to hang around the root zone too long. This will lead to the Knock Out rose leaves turning yellow. Additionally, it is tough for proper photosynthesis to occur without some good sunshine.

Nutrient problems

Other things that can cause yellowing of the leaves have to do with nutrients not being readily available, such as nitrogen. Using a good well-balanced rose fertilizer is highly recommended. Be careful not to use fertilizer mixes that are extremely high in nitrogen though, as too much nitrogen will lead to an abundance of that nice green foliage and few, if any, blooms. I like to give the bushes some alfalfa meal and kelp meal, as these items help build the soil with good nutrients.

The soil’s pH level being out of whack can also cause the yellowing of leaves, so checking this is another item on our checklist if a problem starts. Checking the soil pH a couple of times a season is not a bad idea as a general rule.

Pests

Insects that are attacking the rose bushes can make Knock Out roses have yellow leaves, especially if a spider mite is sucking the life-giving juices from them. Be sure to turn the leaves over from time to time while out tending the garden so you can find an insect or mite problem starting. Catching such a problem early on goes a long way to gaining control, thus stopping larger and more difficult problems later.

Some folks will tell you to use a good systemic spray or granular application of products for general disease control (fungicide, insecticide & miticide) to address all these possible issues. I would not use such a method unless the situation is way out of control and a drastic measure is needed to get things back on track. Even then, use only enough applications to handle the given situation, as too many can damage the soil and many of the soil-borne organisms that help keep the roses healthy are destroyed.

Disease

Fungal attacks can lead to Knock Out rose leaves turning yellow too. Fungal attacks will usually give other signs before the yellowing, such as little black spots on the foliage with perhaps a yellowing circle around the black spot (black spot fungus). Sometimes a white powdery looking substance starts to cover the foliage, wrinkling up the foliage (powdery mildew).

These issues can be avoided by spraying with a good fungicide of choice. Using the least toxic product that will provide the necessary control is highly recommended. There are some very good “earth-friendly” products available for a preventative spray cycle application. In wet conditions, some fungi can become very stout foes and a stronger fungicide is in order.

Environmental

Hot and cold weather changes will also bring about the yellowing of leaves, as the rose bush can be stressed out. Giving the plant some water with Super Thrive mixed into it can help relieve such stresses, as well as transplanting shock and stress.

If your Knock Out rose turned yellow along with falling off of some leaves, this can be a normal cycle of life as well. This is usually lower foliage that is shaded by dense new upper foliage. The lower foliage being shaded is no longer able to catch the sun’s rays nor is it as able to take in nutrients, thus the bush sheds the leaves. Foliage that has become extremely thick can bring about the yellowing for a couple of reasons.

One is that the thick foliage causes the same shading effect mentioned previously. Another is that the thick foliage limits good air flow. When the weather turns very hot, the bush needs the air circulation to help keep it cool. If the foliage is too thick, it will drop some leaves to create air space in an effort to keep cooler. This is part of the heat stress reaction by the bush.

Keep a good eye on your rose bushes and check things out well when a problem is first noticed, and it will go a long way towards enjoyment rather than frustration.

George Weigel’Sunny Knock Out’ rose doesn’t look all that sunny once the flowers open fully.

Q: I have several ‘Knock Out’ rose bushes — the best rose bush ever — and am looking for yellow ones. I know they are available, but the ones I’ve seen have yellow buds that open to white. Are there any yellow ‘Knock Outs’ that have a yellow flower?

A: ‘Sunny Knock Out’ is the one and only yellow-flowered rose in the ‘Knock Out’ series, and I know what you mean about fading. The buds are nice and yellow, but within a day or two of opening, the plant looks like it’s got yellowish-white Kleenex hanging all over it. It’s my least favorite of the ‘Knock Outs.’

There are a few other shrub roses, however, that are decent alternatives.

The best one that comes to mind is ‘Sunsprite,’ a shrub rose that grows to about 3 feet by 3 feet and blooms heavily in a fairly stable yellow color. The flowers also are fragrant. The down side is that it’s quite as bullet-proof against disease as ‘Knock Out.’ You may see a bit of black spot on it.

Another possibility is the shrub-like mini rose called ‘Baby Love.’ It’s an older one but better at holding its yellow than ‘Sunny Knock Out.’ Unfortunately, it’s also not as disease-resistant as ‘Knock Out.’

‘Carefree Sunshine’ is another shrub type you might run into that’s reasonably disease-resistant and also reasonably color-stable, although the yellow is softer right off the bat and not in-your-face sun-golden. It also has a bit more of a rangy habit.

And finally, the ‘Easy Elegance’ series of cold-hardy, disease-resistant roses has a bright-yellow upright called ‘Easy Elegance High Voltage.’ I’ve never grown it or seen it first-hand, but this whole series is one of the best on the market. This particular one has double flowers of rich yellow. It’d be worth the risk, I think.

Anybody else have suggestions?

Knock Out roses are some of the easiest, most rewarding roses to grow! Our yard has 12 fuscia and light pink Knock Out rose bushes. The joy of Knock Outs is their constant blooms from spring until fall. Surprisingly, these rose bushes can grow to be quite large if not maintained. Neglecting them is easy since they require little upkeep and are nearly impossible to kill. I’ve neglected a few of mine to the point of needing some serious pruning. Now is the time to prune roses, so let’s take a look at a few tips on How and When to Prune Knock Out Roses.

This is embarrassing. Just look at that rose bush! I measured it at a sprawling 9 feet tall. Insane! I didn’t even realize Knock Out roses could grow that high. But wow, this one looks like a hot mess.

When to Prune

The beauty of Knock Out roses is that they can be pruned nearly any time without sacrificing beautiful blooms. Here in the south, we can expect the first flush of blooms around Mother’s Day in early May. This will be the largest flush of blooms. Then the plant will enter a resting phase and then burst with repeat blooms every few weeks. Maintainence pruning can be done during the resting phase. It is also a good time to cut off withered blooms, but not necessary.

Heavy pruning though should be done in late February in warm, southern climates or in March for the moderate to cool climates. The only time I do not recommend pruning is in the fall. It could trigger new growth that will not have time to harden before winter. One exception is if you live in the deep south then pruning any time of the year is acceptable.

Recommended Pruning Tools

As a brand ambassador for Troy-Bilt, I have the opportunity to try and review a multitude of lawn and garden tools. Listed below are 3 of my favorite and most used pruning tools. (Amazon affliate links provided for your shopping convenience)

  • Leather Gardening Gloves
  • Bypass Pruner
  • Telescoping Bypass Lopper
  • Cordless Hedge Trimmer

When trimming roses for floral arrangements or controlling overall shape, I really love my Troy-Bilt Bypass Pruners. They are very sharp, cut through rose stems like butter and fit nicely in my hand.

For woody rose stems over 1/2 inch thick, I recommend using a telescoping bypass lopper. This particular lopper has adjustable telescoping handles, allowing you to easily prune thick, thorny branches without having to reach your hands inside the bush.

This recommendation might surprise you but hedge trimmers can be used on Knock Out rose bushes. We have several Knock Out’s grouped together to form a hedge row. Maintaining and shaping a rose hedge is easy when using this cordless hedge trimmer.


How to Prune

Use a clean and sanitized hand pruner for stems less than 1/2″ or a lopper for stems over 1/2″ inch. Cut the stems back to a 5-leaf grouping or an outward-facing bud (if pruning during the growing season). Remove and discard any dead, crowded, crossed or rubbing branches. The goal is to open up the plant’s center and eliminate unnecessary suckers or random shoots. Cut the rose bush back by 1/3 to 1/2 the size. With severe heavy pruning, the plant can be cut down to 18″-36″ depending on how large the rosh bush was.

Tip: Wipe off the cutting blades of the pruner with antibacterial wipes before moving to a different rose bush.

I severly cut that 9 foot tall bush back to about 30″ high. New growth has appeared within just one week since pruning.

Here are a few before pics of the overgrown rose hedge.

And here is the hedge after being trimmed with the cordless hedge trimmer. It needs a bit of fine tweeking with the hand pruner, but overal looks much better.

Start fertilizing with a quality, slow release rose fertilizer in April or at the first sign of significant new growth. In just a couple months the rose hedge will be bursting with blooms look even better than this!

I can’t wait to see how healthy and strong the roses will be this year!

Why are my knockout roses not blooming?

Knockout roses are gorgeous. They are fragrant. They add color to your garden and if you are like most people who add them to your garden you look forward to watching them bloom each spring and continue their blooms throughout the summer and into the fall.

Unfortunately, for a lot of our customers they experience more frustration than joy while waiting for their roses to bloom.

Why?

There are several reasons why your roses may not bloom.

Not enough sunlight – These roses need a lot of sun. Unlike many things in life, this is quantifiable. Roses need at least 8 hours of sun a day. If there are nearby trees or shrubs that shade your rose bush for even part of the day, chances are they will not bloom well. In one case we realized that it was not a building or a tree that was causing a customer’s problem but a van that parked in the same spot every day blocking the light for several hours of the day. Yes, these bushes are that picky.

Too much food – When you feed roses too much they will not bloom. They may become fuller with more healthy looking leaves but they will not bloom. Try not feeding them for a while and see if this helps. When you do feed them, start with a slow release fertilizer.

Improper watering – Knockout roses need to be watered from below. Watering them with a sprinkler may actually spread diseases such as black spot. Try to keep the leaves as dry as possible when watering.

Dry soil – In an earlier post we wrote about the benefits of mulch. Mulching around your rose bushes will help to hold in the moisture and keep it consistently moist.

Do you have beautiful knockout roses you would like to share with us? Do you have a secret to growing these bushes that was not mentioned above? Email us and let us know.

Knockout Roses

Everyone loves roses, and one of the most popular varieties on the market is the long-lasting Knockout Rose. Knockout Roses have earned their popularity by having a consistent bloom throughout the summer, by being easy to grow, and by not requiring the special care of other hybrid rose types. Knockouts are cold tolerant up to zone 5 and are heat tolerant throughout the United States.

Plant them individually among other shrubs, annuals, and perennials in mixed beds and borders. Plant them in large groups to create a colorful hedge or along a foundation to provide a bright border. For best performance, we recommend cutting them back every year in early spring after the last threat of frost has passed.

Knockout Varieties

Not all varieties available at all locations – call your closest Meadows Farms location to ask about availability.

  • RED KNOCKOUT

    One of the most popular roses in the world today, primarily due to its low maintenance, superior disease resistance and incredibly long period of bloom, with seemingly endless cherry red flowers; all roses need full sun and well-drained soil.

  • PINK KNOCKOUT

    The blooms on this hardy shrub are individually small but are in such big clusters the visual impact is stunning; beginning in spring and continuing throughout the summer and fall, even to the first frost, this shrub will deliver glorious color.

  • DOUBLE KNOCKOUT

    This carefree landscape rose has all of the great features of Knock Out plus the added bonus of fuller blooms with twice as many petals; cherry red blossoms and deep purple fall foliage provides your garden three seasons of interest.

  • RED DOUBLE KNOCKOUT

    Plant this carefree landscape rose anywhere you need low shrubs and continuous color; a very low maintenance shrub great for along walkways or in the garden; cherry red blossoms and deep purple fall foliage provides your garden three seasons of interest.

  • WHITE KNOCKOUT

    Pure white single blooms that really pop against the dark green and burgundy foliage; a lovely citrus fragrance; blooms continually from spring to fall; great for sunny shrub borders or containers.

  • Why are my roses changing color?

    Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

    Question from a Landscape Alert reader

    “Several friends and I are confused and bewildered by our gardens this year. I have a rose bush that’s well established and has always been pink. It’s a J & P rose although the tag has long since disappeared. This year the rose is blooming with flowers that are yellowish-peach – more like a Peace rose than the vibrant pink it has always been. My mother and one of her neighbors had irises that bloomed different colors this year than last – Mom’s was a dark rust color last year, and this year it’s maroon!”

    Answer

    It is not unusual for roses to “change color.” A minor change occurs when cooler weather intensifies pink-to-red shades, or age and hot weather fade them. Knock Out ‘Blushing’ rose flowers, for example, are medium pink in cool springs like this and in fall, but a washed-out, nearly-white in summer. The ‘Rainbow’ and ‘Sunny’ Knockout rose marketing capitalizes on the fading of pastel pink and yellow petals as they age, emphasizing that at any one time there are deeply colored buds, pastel newly opened flowers, and pale to off-white older blossoms. The contrast is greatest, and those plants are most attractive in cool weather. Some of our Master Gardener volunteers have complained they are quite disappointed in the “washed-out” summer appearance of those varieties.
    The second type of color change is due to the fact many roses are grafted, so the branches are one variety and the lower root system is a hardier rose. If those lower roots sprout branches, they may appear different in leaf size, shape and flower color. They are more likely to have such sprouts when planted shallow, or if the top branches are all killed by cold temperatures. Around Monroe, there are many identical roses near homes that bloom abundantly at the same time in June; two-inch, dark red flowers with prominent yellow centers. Rosarian Nancy Lindley told me they are most likely the variety ‘Dr. Huey,’ which is often used for the hardy rootstock, and those roses all probably started out with branches and blossoms of a different variety such as a less hardy tea rose.
    The third change happens when one branch actually has a mutation affecting blossom color. Many of our colors started as a single odd branch, called a sport, such as the branch of pale pink roses on a Red Knock Out rose that became a new variety, Knock Out ‘Blushing’ rose when many buds from the branch were grafted onto other rootstocks. One Knock Out ‘Blushing’ rose in our demonstration gardens either reverted (mutated back), or it was grafted onto the red version, because we have a red-flowering branch near the base.

    Irises and color change

    Irises are far less susceptible to the color changes described above in roses. The MSU Extension educators on our conference call this morning agreed it is far more likely that a different variety won the competition for space for some reason. One colored variety may have been killed out in one or two seasons by severe borer attack, allowing a seedling or stray rhizome of another variety to proliferate. The successful plants may be blooming for the first time even if they have been multiplying in the spot for a couple of years or more. Few gardeners keep track of which iris variety was planted where and when, nor are they careful to deadhead and remove seedlings. So reports of color change are not uncommon.


    Rose reversion.

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