Welcome to our Page on Late Spring Freeze Damage to Roses
Ann Peck graciously wrote the report below on late spring freeze damage. I would like to thank her for taking the time to do so and we hope you benefit from it. As always please feel free to email us with any specific questions and we'll do our best to answer them.
About Freeze Damage to Roses
What is Freeze Damage?
Freeze damage happens when the air temperature drops below the temperature at which the 'water' in roses freezes. Water in roses isn't pure water, but carries sugars and other natural chemicals so freezing in roses occurs below 32F. When the water in a rose freezes, inside individual cells ice crystals form and cause breaks in the cell wall. This causes localized damage in the leaves and small stems. Inside mature canes the xylem and phloem cells that are the 'blood vessels' of the plant can also break, and the lack of nutrient movement causes major damage to the canes and their leaves and stems.
What does Freeze Damage look like?
Freeze damage makes the roses leaves, stems and canes look as if they dried out. Newest leaves, the ones that were growing actively when the freeze began, will often look almost burned. Older leaves are cut off from their source of 'water' and may curl up and look brittle and will shatter as if air dried on a hot summer's day. Some less damaged leaves will look bruised.
Different roses (even in the same bed) may have different symptoms, because they have different genetic makeup. Some will show damage quickly, others may look OK for a few days only to look brown after four or five days. Some may worsen as time goes by.
Other roses may survive the same freeze with no damage.
How can I tell for sure that my rose is damaged?
The leaves will be the first sign. Usually when you approach a rose bush, all you see are darker colored upper surfaces of the leaves. When roses' leaves and stems are freeze damaged, there's no longer enough water to keep the stems rigid and you'll see the undersides of some of the leaves. Leaves that were flat may curl or fold up or become wrinkled.
Stems will no longer be rigid; you can squeeze thicker stems gently between your thumb and forefinger, and they give readily. Healthy stems resist squeezing.
Canes are even affected by freezes; some that were actively growing will turn a purple black. Other one or two year old canes (the ones that are still green but don't have bark on them yet) may become wrinkled and furrowed. When this happens it's a sign that the cane has lost its ability to transport liquids and to maintain its rigidity.
What can I do about the damage?
In looking at my roses this week, I've come up with a classification of damage:
Tolerable damage and Intolerable damage.
The rose can live with tolerable damage, because that includes leaves that don't look good, but that are still an important part of the plant's vascular system and that the plant needs while it recovers from the freeze damage. That also includes stems that are alive and have chlorophyll in their outer cells contributing even a small amount to keeping the rose going.
Some damaged leaves are more susceptible to fungal infections. I saw some black spots on roses in my garden today and I have never before seen fungi moving in on leaves that are that young- so we will spray them with fungicide.
I expect most damaged leaves to fall off and be replaced by new leaves. But if the roses choose to continue to use them for a while, so be it.
Intolerable damage is damage the rose would be better off not having, damage that will affect the overall health of the plant for the rest of this year.
Stems that are withered and furrowed will not live long; the faster they are removed, the sooner the rose will grow a replacement.
Damaged leaves on otherwise healthy stems are a bit harder to handle.
First lets consider the leaves on a one-year-old cane:
Many roses will hold onto the leaves until they are ready to replace them as one of the axilary buds (PZ note: a bud is also known as a bud eye) becomes active. At that point the same thing happens as would happen in the fall- the rose forms an abscission layer and the leaf drops off.
On a two-year-old cane of a shrub rose or a climber, instead of a leaf the second year, often a stem emerges with leaves and a flower bud. Yet that more complex growth is as liable to freeze damage as the individual leaf that preceded it. The good new is that the dormant axilary buds are still there, still ready to kick in and grow. (See illustration of Rosa laevigata at right). In the case of the illustration, the rose has its greatest growth over winter and had just put out massive new growth in late March.
It was and remains in high gear and is already abandoning freeze-damaged new growth with more new growth.
Other roses are slower to react and regrow.
What I can do to help them is to finger prune off the dead stems once they are ready to come off- they will come off easily, so that the growing conditions for the new growth are better. I plan to dust these plants with sulphur as a low impact fungicide.
Roses grow healthier when dead materials aren't in contact with living tissue.
Some Hybrid Tea roses have canes that burn in the sun, for those retention of the dead leaves is better while the rose regrows its leaves. But if the leaves become black and rotten, they are better off gone, because there are fungi that live on dead plant material that can cause damage to otherwise healthy roses parts.
Dead and dieing canes do not contribute to the overall health of a rose bush.
What is my garden going to look like this summer?
Among my once blooming ramblers, both those descended from Rosa multiflora and those from Rosa wichurana look equally healthy and I see buds on both that don't squish when I gently pinch them. I hope to get some blooms from them.
In my garden, among the once bloomers the gallicas appear undamaged as do the centifolias. The damasks, to my surprise, are variable- some look good (Leda , Autumn Damask and Omar Kayyam) and one looks terrible (Trigintipetalia).
Repeat blooming roses will again have blooms once they have regrown healthy canes and foliage. We need to keep a watch on our roses to make sure that any canes that show damage later this season are removed.
Could I have done something to prevent this damage?
I grow a lot of roses and I couldn't do anything because it became too cold and stayed cold for too long a time.
I protected a few roses that were small and most vulnerable, but a massive protection was not possible.
Had my roses been mounded for the entire winter with organic mulch to protect them from a freeze, the temperatures in the 60F to 80F range that we enjoyed in March would have caused massive fungal damage to the canes as the rotting materials in our mulch came in contact with our rose canes..
We would have lost mature canes down low from that attempt at winter protection. (This happened often enough in previous years that I have learned from on site experience.)
I have said that my garden is the southeastern-most garden in the North American Great Plains. After this cold, I think that the weather that affects the Great Plains extends both farther south and farther east than my garden. The roses that I grow that came from cold hardy breeding programs in Canada are undamaged by this big freeze. These don't have the look of most roses we enjoy, but they have a wild and exuberant look to them that have earned a place in our garden.
Where can I learn more?
Our roses are part of the plant family called Rosaceae, and Rosaceae includes apples and other fruit. There are discussions of how to deal with freeze damage in those crops and those crops were also hit hard by the freeze. Use your favorite search engines to see if anything recommended for related fruit trees could apply to your garden..
You can learn a lot by watching your own roses and their response to this freeze and how they bounce back. Keep a journal of which roses did best and see who hybridized them and what other roses of similar breeding you might like by that hybridizer.
And for your weather history, I'd recommend a visit to http://www.wunderground.com.
Weather underground has a huge network of individual weather stations across this country. When you enter your zip code, it will tell you about personal weather stations near you so you may be able to get a feeling for how cold your garden was and for how long when you go to the daily almanacs for those stations. I keep several max-min thermometers in my gardens because I'm curious to see what temperatures really are where my roses grow.
Should I do anything special this year?
For now, hold off on using heavy fertilizer. Water your roses well and consistently. I keep a rain gauge in my garden and I record rainfall. I know when the plants are getting stressed from lack of water. Knowing the amount of water coming into your garden is going to be important in helping you watch for the appearance of other freeze damage. If you see wilting starting on a cane and you know the garden is well hydrated, then you need to look for damage on that cane. (If you see wilting all over a bush and the bush is wobbly in the ground, then you may have a rodent eating the roots, but that's another story.)
Click here to visit Ann's website
We would also like to thank Ashdown Roses for sharing this very useful article http://www.ashdownroses.com/index.asp
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Last updated September 12,2008