I live in South Africa and have recently had issues with some of my potted roses. On some of the roses, the tips of the flowers were burnt, while on others, the petals would completely shrivel up and dry out within a day of opening. So this past weekend I’ve been measuring the temperature throughout my garden to figure out what the issue was and where I could place the roses. The place that they were in (before I temporarily moved them to a shaded spot) is enclosed by walls on all sides with a brick base. It’s meant to dry laundry but had enough space for the pots.
I also happen to have a Paterson Thermometer accurate to 0.14°C. Turns out … day time temperatures exceed 55°C (131°F) in this area during a mild 33°C heat wave because of the walls and the bricks reflecting and storing heat. Oops.
Temperature for the day provided by multiple weather stations and independent organizations was around 32°C. However, these are the temperatures I measured.
- 9:30 AM 42°C Direct Sun
- 11:30 AM 55°C Direct Sun
- 6PM 29°C Sunset
- 11:30 AM 45°C Direct Sun
- 9:30 AM 32°C Partial Sun
- 9:30 AM 24°C Constant shade
- 6PM 25.5°C Sunset
What’s really confusing is no post or article anywhere on the internet or in books and magazines mentions if the “temperatures” preferred by roses are under 30°C in direct sunlight, including solar radiation, or if this 30°C number is the average temperature reported by weather stations and weather services which is measured in the shade. I give each plant over 1 gallon of water a day, so the area where they were was able to burn them regardless.
My garden receives full sunlight from sunrise to sunset with consistent shadows. My only options are direct sunlight for a full day or complete shade as there are no trees on the western side that block the sunlight until the sunsets below my garage at around 5PM.
So my question is:
- Is the recommended temperature for roses measured in the shade or in the sun with solar radiation accounted for? In other words, if average day time temperatures were 30°C and under (under 90°F) but direct sunlight measured over 40°C (100°F), does this still count as the “recommended” temperature?
- Since the garden has far more airflow and is over 10°C cooler during direct sunlight, will the water be able to cool my plants down enough to not have their petals burn or shrivel throughout the day in direct sunlight? Or should I place them in complete shade?
I know roses are able to grow in my area, many of the houses in the surrounding area have roses. Some in complete shade (However, 90% of them are Iceberg, so this may change things).
I’ve got this same problem…In Kuwait, a couple years ago, temperatures in direct sunlight got up to 70 degrees Celsius (158F). @ReclusiveEagle , Roses in my climate pretty much need to be covered by green (tarp?) cloth that protects them from the sun in summer.
I’m lucky enough to have an alfresco/patio that gets some shade so I don’t use it.
But…I was hoping to get my roses on the outside of the house trained up a wall but I have no way to protect them in the summer. Any ideas?
No idea if temperatures are measured in sun or shade. Do not water the leaves if in direct sunlight…they will get burned. Do you have an area with morning sun and noon shade? That might be the best place to put them. If they are potted can you move them to a cooler area in the summer and then full sun in winter.
Unfortunately no. The far East side of the garden has trees that provide shade till about 9:30am. From 9:30 to 4pm my garden gets full sunlight. The sun’s position is directly above the middle of my garden so the only trees and other places that provide shade, for example the roof line, give shade from sunrise till sunset. My only other option is a corridor that only gets direct sun for about 2 hours a day. ± 1pm to 3pm
I can only say that there are no horticultural temperature specifications that I know of, which are stated in terms of direct solar radiation. I would think that roses are no exception.
I might have to do this. Maybe adding more mulch than normal to protect the roots and prevent evaporation will help? I assume there is a limit where adding more water won’t help. The leaflets and stems on my plants are fine, but the petals themselves are drying out and burning. I think what will help you though is a PVC roof/Corrugated Polycarb sheet. This will diffuse the light, unsure if it will trap heat and increase temperatures since it’s plastic/polyester, but the higher it is above the plant, the more diffused the light will be.
You can also try reflectors/diffusers. They are meant to soften studio lights or the sun for outdoor photography, but it can be used for the same purpose here. The material will reflect harsh sunlight and allow diffused light to fall on the plant and you can cut it. I don’t want to have to resort to that in South Africa since my city is not as hot as yours but it’s an option I guess.
Otherwise time to go down a rabbit hole and build a greenhouse.
I guess in it’s place zones have been adopted in countries like America. In South Africa we don’t really have a zone system and any information on climate types are conflicting. Only information I can really find are on soil types and distribution. My city is kind of like a slightly less harsh Texas/California but we are 4,393 ft above sea level so that changes a lot of things.
Your issue is mainly the fact they are potted. They can withstand tremendous heat as long as their root balls don’t cook. What are they potted in? Hopefully, it’s something which insulates against heat (wood, concrete, foam) or at least plastic nursery cans. Terra cotta and ceramic are the absolute worst as they ARE cooking utensils. They heat up quickly with solar radiation, transmit it tremendously efficiently to the interior and retain that heat for a good while after the direct source of heat is removed. Placing potted or even in-ground roses close to any masonry surface will also cook them quite efficiently. You are aware of how well masonry surfaces absorb, retain and radiate that heat. Your flower petals are going to cook on intensely hot, sunny days. It’s their nature. They are tremendously more fragile than any of the other plant tissues and are only meant to provide for reproduction. They are literally part of the plant’s “ovulation” to encourage fertilization and pregnancy to reproduce the species. It’s the foliage, wood and roots you really need to be concerned about.
Sun shining on the pot sides can literally cook the roots growing against and within a few inches of the sides to death rather quickly. That absorbed heat also cooks the soil moisture out of the root ball and that increased soil/root temperature can lead to fried flower petals, also.
I’ve had several “enthusiastic exhibitor” friends who have used “E-Z Up” portable canopies which they set up, stake against the wind and then move around to shield specific plants from the sun damage to provide themselves with suitable blooms for exhibitions. https://www.ezup.com/?utm_source=google&utm_medium=cpc&utm_campaign=DSA&utm_term=&gad=1&gclid=Cj0KCQjwm66pBhDQARIsALIR2zCZOsnBrOqN0aUZPlzTxVXo5KbtYQoTRoku2o3F2xDe-MaJK1_fQGgaArCAEALw_wcB Not to advertise or promote that brand, but simply provide an example of the product concerned. Anything which can be secured against wind and provide a reduction in heat and light to prevent sun damage should work well. I built a rustic wooden frame over a table upon which to staple gray nylon window screen to grow newly rooted cuttings under to prevent sun scald. It isn’t “hot” here in comparison, but the sun intensity nine miles from the Pacific can be INTENSE and it can fry fragile tissues quite quickly. If I want to have flowers on my micro minis to use for pollen, they must be grown under such shade. I built similar structures over my seed tables to affix plastic hardware cloth to so air, light and rain can get in while preventing the sun intensity and preventing birds from entering and eating the seeds and seedlings.
All of my roses are grown in nursery cans because of the engineered soil the house is built upon. State laws require the soil be stable in earthquakes and that requires it be physically compacted into as close to “bed rock” as possible. There is very little air space between soil particles so there is little chance of roots pushing very far into the soil. Most remain within inches of the soil surface, so pots on plastic sheeting to prevent grass and tree roots from invading the pots is my method. Even when the temps remain “cool” (eighties), many flower petals fry, even with the pots shaded by other pots. I find it’s not only the darker colors but also those with greater scent as they are more fragile than unscented types. Unscented types have a tougher cuticle than scented types and don’t have the oils and alcohols in the petioles to heat up, releasing the scent, which causes them to deteriorate more quickly. It’s what the rose catalogs picked up from the ARS exhibitors decades ago as the “heavy petal substance”. It’s what exhibition and florist roses require to enable them to be handled, refrigerated, shipped and then last many days in a vase. It’s also one of several reasons most of them don’t smell.
As long as your plants are surviving in decent shape and it’s only the flower tissues you’re having problems with, I’d suggest putting the plants as far away from any passive solar collecting masonry surface as possible. Provide good air movement between them and any hot wall, walk or patio and consider some sort of stable, portable shade which you can move as needed and secure against wind if protecting the flowers is the goal.
It’s worth pointing out that even hot climates can have great differences among them–for instance, where I live, the persistently high humidity in summer results in high night temperatures for months on end. In high temperatures during hours of darkness, poorly adapted plants are forced to respire at a high rate, burning energy that might otherwise go into growing and flowering. Soil temperatures can also rise significantly because of the lack of overnight cooling. Many roses are well adapted to surviving these conditions, but they generally do so by halting unnecessary functions like flowering, and typically go into a state of effective dormancy until the conditions improve. Those roses that do try to flower during this time usually have small, poorly developed blooms that last for a veritable nanosecond, assuming that they manage to also run the gauntlet of rose midge, which literally nips them in the bud. Under these conditions, most roses understandably either stop trying to bloom altogether, halting most vegetative growth as well, or they nearly stop. Some will resume growing and flowering once the weather cools a bit.
Since your roses continue trying to bloom in the heat, it’s likely that the humidity there is much lower in summer, which also explains why Iceberg roses can survive in the shade. Here, they would struggle to keep their leaves because of blackspot, even with good sunlight.
It seems to me that your best move is to provide some (not total) shade, one way or another. Shade cloth may be one option, but potted, fast growing trees that cast light shade but are tolerant of your conditions (acacia, maybe, unless you need something even more cold tolerant at your elevation?) might perform the same service in a slightly more aesthetically pleasing way, and potentially at a very low cost. There are crops like cacao that often must be grown like this, with what are called “nurse trees.” Maybe that could work with your roses, too. I have a lot of potted plants and face some of the same problems here; I’ve found that strategically sited pots of taller plants can provide some of the same microclimate modification benefits for smaller potted plants that in-ground trees might.
As someone in a hot climate, I can relate, @ReclusiveEagle !
Yes mulch is very helpful! Definitely mulch.
I completely agree with @roseseek about avoiding the terracotta and ceramic pots. Also I would avoid those air-pots as well as fabric pots, they might work well in rainy climates but they’re way too drying in mediterranean-type climates.
Also as Roseseek noted the sides of the pots heat up a lot. Last summer during peak heat wave I wrapped aluminized car windshield sun cover material (the kind with the air bubbles in it) around the most exposed pots. That, combined with a thick layer of mulch, brought down the soil temperature in full sun from 45°c to 32°c (measured with a meat thermometer stuck into the soil). You can find the windshield cover material in rolls and cut to the size of the pot. Any of them will do as long as it has the bubbles+aluminum combo. It’s ugly as sin but it really works and you can remove it when the heat abates.
In hot climates there tends to.be a good deal more luminosity than elsewhere, so “shade” is not really always a problem, on the contrary. Bright shade, like by a north-facing wall (or I guess that would be a south-facing wall in the southern hemisphere?), can actually be one of the best locations.
You can use a shade cloth as pictured in @Umm_Kulthum_Carter 's picture, I made a similar setup over some of my most exposed pots last summer. The reed screen on the side provides shade from the afternoon sun while letting air through. Yeah it’s a rickety DIY but it was good enough for several weeks of dog days.
A more aesthetic thing is to add a large pergola to shade the roses from mid-day sun, which can be dressed with shade cloth or with climbing plants like grape vines on it.
Similar to @MidAtlas ’ suggestion of potted trees, even without a proper pergola, grape vines can be very useful: I grow a grape-vine in the middle of a cluster of potted roses, and with the proper training of multiple canes fanning outwards (think of it as a modified goblet-training) a dappled shade is achieved below. Grape-vines grow fast in the spring and then in winter it all gets hacked back so they get full sun in the cooler months. Bonus: you will also get grapes
I used to manage a nursery at the beach in Pacific Palisades. We had a client who insisted on planting cast iron planters on her patio facing due west on the bluffs above Pacific Coast Highway. They received direct, full sun all day and literally cooked everything planted in them. Insulating their interiors with bubble wrap allowed fewer plants in them due to the reduced soil area, but the air insulation allowed those planted in them to last longer than they had previously. So, using either thin Styro Foam or bubble wrap inside the containers can help, as long as they are large enough to accept both the insulation and a sufficient root ball for the plants desired.
I do have a massive Acacia in the northside garden. The problem with Acacias is branches continuously fall from them, some even larger than the bushes. So if one of these branches hit any one of the bushes, that will potentially instantly destroy the entire bush. This side also does not get a lot of sunlight as there are multiple massive trees in the area.
The other drawback on the northside vs the southside garden is, on the southside we have a Juniper that supports an entire population of Ladybugs and some of their larvae have already migrated to the rose bushes to deal with the Aphids so I don’t have to use any chemicals to control their populations. The northside does not have any plants that will support the Ladybugs long term. So it’s really a choice between direct sun and natural Aphid control, full shade, or partial sun without the Ladybugs.
So I will have to see if I can figure something else out.
More mulch would probably help. I usually have to water potted roses deeply (1in above soil) twice a day in the summer here…One time deeply (morning), one time lightly (twilight) and they seem to like that.
Anyone got ideas for protecting roses on arbors/trellises/arches from sunburn? I would love to get a climbing rose and train it on an arch, but I can’t figure out a solution for the summertime…it would be a waste to get a young climbing rose that won’t last a year because it fries in the summer. Even palm trees here get sun burn – but they’re hardier and just come back when things cool down. Unprotected roses probably would not be able to withstand that amount of heat and direct sun.
You may have already seen this, and if so, perhaps it isn’t a great help, but there has been a map published that converts African climate zones to equivalent USDA zones.
ReclusiveEagle, being in South Africa, have you contacted Ludwig’s Roses for any advice? Surely they might have some tips to mitigate your heat issues?
Wow… And I gripe about my Texas extremes…
I am folllowing this thread. I tend to lose roses every summer to the heat, but wonder to what extent drought and poor nutrition combined with the stress of chili thrips might be major contributing factors.
The most carefree as a group for me tend to be a few china roses, but some modern shrub roses do quite well in the hot, sunny front yard.
Moving forward, I do have the intention of planting e.g. “Palo verde” tree (Parkinsonia sp. in Fagaceae, having sparse foliage that would allow a great deal of filtered light) and similar semi-shade trees. I am hoping such won’t compete too much for nutrients, but don’t really know what to expect.
I really want to be environmentally friendly, but moving forward, I think I will need to use irrigation and fertilizers more that I would ideally like if I am going to continue with my hybridizing in this climate.
Philip, try to find a Desert Museum Cercidium. It has no thorns; is sterile so no seedlings and far less litter than the usual Palo Verde. I had one in Encino. It’s a gorgeous, easy to live with tree.
There are of course many options when it comes to acacias (Acacia s.l.: Acacia, Vachellia, Senegalia) and similarly useful members of Fabaceae, which as Philip noted is a family particularly rich in trees that cast light shade and demand relatively little in the way of resources. They don’t all necessarily create problems for plants underneath. Parkinsonia can be great choices, as can be some of the Vachellia, like V. farnesiana (formerly called Acacia farnesiana) if you’re mindful of the thorns. There are mesquites (Prosopis) native and adapted to a number of very hot, dry regions of the world, too; they’re also thorny in many, but not all, cases. Some members of the family might actually cast too little shade, like Genista aetnensis (also a non-prickly and somewhat more cold-hardy option where extremely light shade is wanted; it’s exquisite).
I live in central GA. We are typically very hot in the summer. I’ve tried double potting my roses, especially young own root plants. That seems to keep the soil from drying out as quickly. However, we rarely get hotter than 100-105 F.