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

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.


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.


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.


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.

How to Care for a Rose With Yellow Leaves

A previously healthy rose bush that suddenly shows signs of disease is cause for alarm and dismay among rose gardeners. One of the most common causes of yellow leaves in a rose bush is a fungal infection called black spot. When a rose contracts this fungus, black spots will appear on leaves the leaves will turn yellow and then drop from the rose bush to the soil. Although the prognosis for black spot is bleak, a gardener has several options for minimizing long-term damage.

Clip off the infected leaves and branches from the rose bush with the pruning shears as soon as possible after you find yellowing leaves. Remove every unhealthy, yellowed leaf and branch from the rose bush at the nearest point where the leaf or branch intersects with the next largest stem or branch.

Discard the removed foliage and stems directly into the garbage bag. Do not compost these leaves. Clean up any fallen leaves and foliage that are littering the ground beneath the rose bush and discard these also.

  • A previously healthy rose bush that suddenly shows signs of disease is cause for alarm and dismay among rose gardeners.

Make a fungicidal spray. Dissolve the 1 tsp. of baking soda in 1 qt. of cool water. Add two to three drops of dishwashing detergent to the baking soda and water and stir the ingredients well to combine them. Pour the mixture into the spray bottle. Alternatively, you can also purchase a fungicidal spray appropriate to use on roses from any garden center.

  • Add two to three drops of dishwashing detergent to the baking soda and water and stir the ingredients well to combine them.

Spray fungicidal spray onto the remaining foliage of the rose bush (and any surrounding bushes to prevent the fungal infection from spreading). Apply the fungicidal spray two to three times per month to the rose bush. Always reapply the fungicidal spray after any rain showers.

Consider removing the entire rose bush if the fungal infection is so severe that the rose bush does not respond to your pruning and fungicidal spray applications. If one-third or more of the entire rose bush has yellow leaves or is bare because leaves have fallen, the fungal infection is likely too severe to treat. If the yellowing leaves do not decrease after you begin treating the symptoms but rather the infection continues to spread, the infection may be too severe to control. In this case, removing the plant is best, to prevent the infection from spreading.

  • Spray fungicidal spray onto the remaining foliage of the rose bush (and any surrounding bushes to prevent the fungal infection from spreading).
  • Consider removing the entire rose bush if the fungal infection is so severe that the rose bush does not respond to your pruning and fungicidal spray applications.

Some rose bush varieties that are resistant to blackspot fungal infections. These varieties include "Caldwell Pink," "Knock Out" and "Simplicity" shrub roses "Cathedral," "Pretty Lady" and "Sun Flare" floribunda roses and "Cary Grant," "Lady Rose" and "Pristine" hybrid tea roses. This is not an exhaustive list.

What to Do If Your Knockout Rose Bush Leaves Are Turning Yellow

Knockout rose leaves can yellow because of quite a few reasons. Solving the problem and keeping your roses of all breeds healthy, requires proper care and attention. Most roses stay healthy unless they are suffering from some kind of deficiency or over feeding of water.

Cold and Heat

Your knockout rose leaves could turn a yellowish color owing to extreme weather. They are not resistant to heat or cold and will certainly wilt in both weather conditions. Keep them at a constant temperature between sixty and seventy five degrees.

Watering and Feeding

Do not over water the knockout roses. The roots can drown and effectively make the rose shut down. Do not under water them, especially in hot weather, as they will wilt quickly.

Soil and Atmosphere

Keep the Ph balance in your soil. Some roses respond to different levels of Ph balance and clay soil can depreciate the quality. Do not overly spray your roses with chemicals. You will effectively over medicate them. Make sure there is enough nitrogen reaching the roses. If the knockout rose is planted amongst others of the like and it is the only one not doing well, it could be the rose bush itself that is ill. Keep the roots cool and use high nitrogen fertilizer.

Knock Out Rose Turned Yellow - Help, My Knock Out Roses Have Yellow Leaves - garden

Gotta love those knock-outs. by perennialpal

TheGardenLady received these two questions about Knock Out roses from Mary and Diane respectively.

I planted eight knock out roses in the sun last year and they bloomed. After blooming the first year I put mulch on the base of the rose bush and the ground was not frozen. This spring I cut them back slightly the first bloom was great. We went on vacation and had a bad rain storm and the roses stopped. What am I doing wrong?

Last Spring (2008) I planted 9 knock-out roses. They grew and bloomed fairly uniformly. This Spring they looked very healthy, and all burst into bloom at the same time. After the first bloom, two of them turned a very light green. I have checked them for over/under watering. Fertilizing is not an issue as I have fertilized them all uniformly. The other 7 are beginning to bloom for the second time, but these two do not have new buds. They do not look like they are ready to die. I can find no evidence of insect damage either at the root or leaf level. They are all planted in the same bed in one grouping for concentrated color (i.e. within feet of each other). I am stumped as to what to do. Any ideas?

TheGardenLady imagines that you must have a fantastic show of concentrated color with those beds Knock Out Roses. TheGardenLady has just two Knock Out Roses and the floral show is amazing.

Two questions that are similar but not the same however the treatment of the roses should be the same.

The first lady had Knock Out roses that stopped blooming after heavy rains knocked off the flowers and haven’t started reblooming.

The second lady has some of her Knock Out roses in one bed that are not blooming.

Roses need sun and lots of it. The first lady had a major storm that obliterated her roses. TheGardenLady does not know if rains continued as they have for an exceptionally long time this June in the Northeast. Rain and gray weather are not conducive for flowering.

Before TheGardenLady gives both of you some suggestions to help your Knock Out roses, let me explain to the second woman that for plants even planted in the same bed, not all parts of the bed are created equally. Sounds silly, but parts of the soil just a few feet away from other parts might not be quite as ideal- in the GardenLady’s property there is lots of shale in the ground which can affect the water drainage. And even though you fertilize your plants equally, some plants might need more fertilizer than others. Both of you can try trimming back your Knock Out roses that aren’t showing buds. You can do this any time of the year to stimulate new growth. Trim no more than 1/3 of the shrub.

Even if you don’t trim, you must use a fertilizer that has a high phosphorus component in it to stimulate rose flowers to bloom.

When you read the fertilizer content on the label you will see 3 numbers. The container might say 10-10-10 or something like that. The three numbers on your fertilizer container represent Nitrogen (N), Phosphorus (P) and Potassium (K) in that order. The number is the % by weight of the nutrient contained. For a simple understanding of what these chemicals represent, the first number, Nitrogen is good for growing new leaves on a plant, encouraging good plant growth and the healthy green color of the plant. The second number stands for Phosphorus. Phosphorus is for encouraging more flowers, fruit and seeds and a strong root system. And the last number is for Potassium which is a catalyst for many plant functions like forming strong stems and fighting disease, etc. These are the three nutrients that are needed in greater amounts by plants. They are called the major or macronutrients.

It is recommended that to have a lot of flowers on your perennial plants like Knock Out Roses, once they are about one year old, is to feed them a fertilizer that encourages flowering. These fertilizers are referred to as bloom booster type fertilizers because they have a very high Phosphorus number on the label. TheGardenLady has used Shultz BloomPlus plant food very successfully on Knock Out Roses and other flowering perennials and annuals both when she worked on a show garden and on her own flowering plants. Shultz label says 10-54-10 so you can see how high the phosphorus % is. There are other brands that make bloom booster fertilizers- just look at that middle number. The reason TheGardenLady does not use bloom booster fertilizer on perennial plants the first year is to allow the plant to become established and acclimated to their new location in her garden before forcing them to bloom.

And be sure to read the label and FOLLOW DIRECTIONS exactly. Scultz includes a measuring spoon in the box and tells you exactly how much water to use. You do not want to guess when you give the food because the plant fertilizer or food has been scientifically formulated and the manufacturers know what will work and what will harm. You don’t want to burn or overfeed the plant. Too much of a good thing may make it a bad thing.

Another thing that some top nurseries recommend to add to all their plaints is NOT a fertilizer but is a vitamin and hormone supplement. It comes in a small bottle and is called SUPERthrive #1 plant health EXTRA LIFE. You add a few drops to the plants WITH the fertilizer. The label says it should be used all the time but some people feel that this vitamin-hormone supplement is particularly beneficial to use when your plant is under stress. Read the label when applying . You can buy it in stores like Wal Mart.

I always have a weakness for knock out roses. by kitty kitty @.

Try these suggestions and you should have your Knock Out roses reblooming this summer if there is lots of sun. Let TheGardenLady readers know if you have success. We would love to see photos of your roses.

Why have the leaves on my rose suddenly turned yellow and fallen off?

Hi, I have a rose that until January was flourishing then all of a sudden the leaves have started turning yellow and falling off (new and old alike). The buds aren't opening properly and when they do the roses have a shrivelled appearance. I have watered and fed regularly, and sprayed for diseases and insects. My rose is a Lasting Love standard beside a fence which I have tied to the fence for support. Any suggestions on what could be wrong with my bush? Thanks, Rachelle.

This is die-back which can be caused by a number of things including black spot, mildew or rust. Die-back is a symptom of disease and not necessarily the cause. Cut away the infected branches to beyond the infected wood, make sure this is done on a dry sunny day. Seal the wounds to prevent disease entering the plant. Pick up any infected leaves that may have fallen around the rose to stop disease spreading. The disease could have been carried on dirty cutting tools, make sure they are clean by sterilising with methylated spirits so disease can't be spread to other plants. Try and stake the rose rather than tie it to the fence, as this will cause less damage to the rose. Spray with a spray suitable for fungal diseases on roses - check at your local garden centre.

Keep your rose well watered – deep watering every 3-5 days rather than light sprinklings of water and feed it during spring, summer and autumn with a specially blended rose fertiliser such as Tui Rose Food. Tui Sheep Pellets are also great for roses - they are sheep pellets and nitrophoska mixed together in a pellet so have the added benefit of improving the soil as well as feeding the rose.

Double Knock Out roses are very easy to grow. Give the plants full sun in a garden spot with fertile, well-drained soil and space them about four feet apart to allow good air circulation. To keep the blooms coming, fertilize your Double Knock Outs after every bloom cycle with any good rose fertilizer.

For one thing, if you want to keep it blooming continuously, you need to groom it. This means clipping off the faded flowers. If you leave them, they’ll form rose hips with seeds inside and flowering will slow to a crawl. Grooming ‘ Knock Out ‘ rose every week or so spurs new growth loaded with new rose buds.

Watch the video: How to Troubleshoot Yellow Leaves on Knockout Roses