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You may see guides and people often say that the reason for your rose leaves turning yellow is dieback. But dieback is just a general term that means that something is stressing out your rose tree or bush. It takes some detective work to establish exactly what is making your rose plant unhappy. It could be pests or diseases, its growing environment or even how you’re treating it yourself.
In most cases, it is probably black spot or rust disease, both these diseases cause the leaves to turn yellow, and I do cover them at the bottom of this guide. However, both black spot and rust are very common on roses and easy to identify so if this is the cause, you probably already know.
Here are some of the other main reasons why your rose has yellowing leaves and what to do about them. Let’s start at the beginning.
What is transplant shock?
If you’ve just planted a newly-bought rose plant, whether into a container or into a flower bed, your plant is stressed out at the move. It has a different location, probably with a different amount of sunlight than before. The soil is new, and maybe it’s not as sheltered as it was, plus; the roots have probably been disturbed too. And perhaps it has received too much fertiliser, which can burn the roots causing the leaves to turn yellow and drop.
Rose plants, and all plants, in fact, take time to adapt to their new surroundings. They put their strength and energy into establishing their root system. And the leaves may not receive as much water and nutrients as they need. They turn yellow and even fall off.
What to do
Just be patient and take good care of the rose tree. I have advice for this in the article How to grow and care for roses. Those who plant their rose tree in a container should read Growing roses in pots instead.
pH of soil
What is the pH of soil?
The pH of the soil you planted the rose in may be too high. pH is a measure of how acidic or alkaline the soil is. Use a soil pH testing kit to determine what the pH is. Roses need a reading of around pH 6.5 for their best life. This is slightly on the acidic side of the scale.
What to do
You can adjust the pH of the soil by adding the appropriate minerals to bring it into line. Increase the pH (less acidic) with a lime-based compound; decrease the pH (more acidic) by adding a sulphur compound. If you are unsure and there no sign of black spot, maybe give the rose some specialist rose feed and see how it gets on. I good layer of farm manure dug into the soil can help bring on roses.
Sunlight and heat
How do sunlight and heat affect the leaves?
If it’s the lower leaves of your rose that are turning yellow and perhaps dropping off, consider a lack of sunlight as the problem. Maybe the leaves of the upper part of the rose are throwing shade over the bottom of the plant. The foliage at the bottom isn’t getting enough sunlight for healthy growth.
Too much radiant heat can also turn the leaves yellow. What happens is that the dark soil, mulch or stone below the plant throw up the heat that they retain into the plant. This causes heat stress on the plant. One of the results is that the leaves turn yellow.
What to do
Accept the sunlight issue as part of the rose tree’s life and just pick up the fallen leaves. If the top of the rose is overshadowing a lot of the lower part of the tree you can prune it back. (See How and when to prune roses for details.)
I have found that this is not a problem if you don’t let your roses get too tall and prune them every spring so that the majority of the growth is all from the current season. I like to cut my roses back hard to 20-30cm (12 inches) above soil level.
For heat stress, try a lighter colour mulch (perhaps cedar bark) under the plant.
Is over-watering or under-watering the problem?
Yes. Both over- and under-watering result in your rose leaves turning yellow and perhaps dropping off the plant. If you’re under-watering, the leaves may curl up and become brown and crispy later on. If you’re over-watering, the leaves stay a bit plump as they turn yellow. They could then also fall off and the rose can also start to droop.
Both under- and over-watering could result in a water-logged plant if the excess water doesn’t drain away properly. This not only turns the leaves yellow, but invites diseases such as root rot to develop.
What to do
For more details about root rot that may result, check out this article. The article also explains what to do about over-watering.
If you’re under-watering and still have standing water around your rose bush, add some organic matter to help with draining and breaking up clumpy soil. If you have your rose in a pot, check the pot has drainage holes in the bottom and that you put crockery in the bottom to stop the holes from becoming blocked up.
What is rose rust?
Two fungal diseases can cause your rose leaves to turn yellow. Let’s start with the least harmful one. Rose rust appears in spring and summer. It shows up as orange and black boils on the underside of leaves and yellow spots on the top.
What to do
See the Rose rust section of the Rose pests and diseases article for help in identifying and solving this problem.
Rose black spot
What is rose black spot?
Rose black spot is one of the most severe fungal diseases of roses. You can spot it by the rapidly growing black or purple patches surrounded by yellow on the upper leaf surface. It’s usually not fatal but it does look dreadful and quickly spreads.
What to do
I have a guide dedicated to rose black spot here, which you can read to find out about this harmful disease and how to combat it in your roses.
Both Black spot and Rust are very common diseases that cause the leaves to turn yellow on roses. The good news is that you can help prevent these diseases in the first place. This is what I do as it’s better to prevent that and try and treat them once they appear. As soon as the leaves open in spring, I spray the leaves with a rose fungicide that is labelled for Black spot and Rust. This treats most diseases, and you can even get sprays that also control aphids like Rose Clear, so they are a 2-in-1. I spray the roses again every few weeks. I usually like to avoid fungicides and pesticides if I can, but with roses, I have found it to be the only way to prevent and treat Black spot and Rust.