Heat Wave Champions
Master Rosarian, Santa Clarita Rose Society
This article is a 2016 Award of Merit winner
Originally published in Rose Ecstasy
Every year I look forward to June Gloom. It’s usually overcast and cool, with occasional light drizzles in Santa Clarita. The roses often produce great color and size during June Gloom. But this year, June Gloom never quite happened except for a few days during mid-June. The first three days of June in Santa Clarita began at 100 degrees followed by another week into the 90’s.
We had decided to exhibit our roses at the Orange County Rose Show if our roses bloomed in time. So, on June 8 when we returned from a trip to Northern California (we had a designated daily water person during our trip), the heat had arrived in full force. We got up early every day several days before the rose show, to cut blooms and put them in the floral fridge. By Friday, June 10 we had plenty of blooms in the fridge, but the weather forecast predicted possible drizzles for rose show day in Newport Beach where the show was being held. Wow! It drizzled all morning from 6 am to 10 am while we were trying to prep our roses for entry. Fortunately, I had insisted that Bob pack our 10 x 10 pop-up tarp in the van. That worked out well for us, so we were able to prep our roses under cover, but we still had to carry our roses over to the exhibit tent, so everybody’s roses and our bodies were soaking wet. But we still managed to win 11 trophies at Orange County, and it was a nice day once the rain stopped and the sun came out.
We got a brief cool down the 3rd week in June, then we were hit with a sucker punch in the 100’s for another week, with the hottest day hitting June 20 at 114 degrees.
That pretty much ended June Gloom. Most of the rose blooms fried like crispy corn flakes. The foliage was burning too. This was the hottest June that I can ever remember since we moved into this house 50 years ago.
The roses looked horrible, and the petunias were dying, but we continued daily watering to prevent the roses from further stress. I remember getting out of the swimming pool the evening of June 20, and as I walked past my huge 7-foot tall English shrub rose 'Radio Times', I was awestruck by the health and freshness of this bush that was covered with more than 80 perfect pink blooms. The buds, blooms and foliage were unscathed by the heat. How could this be? This rose grows in all day full sun, up against a southwest facing block wall. In 114 degrees? Since it wasn’t quite dark yet, I grabbed my iPhone and snapped some photos of 'Radio Times', and a few other roses that had made it through 114 degrees that day. Early the next morning I ran around the yard snapping some more photos before the predicted 110 degrees made a second pounce on our roses. I wanted to report on how various roses did or did not survive the heatwave.
As a group, it seems that many of the pink roses (except OGR’s) handled the heat quite well. 'Gemini', 'Hot Princess', 'Big Time', 'Johnny Becnel', and 'Radio Times' sailed right through the heat without batting an eye. An exception is the foliage on the miniature 'Joy' that burns terribly even in milder temps of 85 degrees, although the blooms hold up well. 'Joy' needs to be shaded, especially when grown in containers, whether own-root or grafted on rootstock.
As expected, 'St Patrick' blooms held up well but some of the foliage burned. This is typical of 'St Patrick', where the blooms are like cast iron, but the foliage is very sensitive in extreme cold or hot weather. In other yellows, floribunda 'Golden Holstein', hybrid tea 'Aloha', miniatures 'The Lighthouse' and 'Behold' held up amazingly well. All of those yellow roses are growing in full, all-day sun, and Behold grows in a container on our cement pool deck, so I was totally surprised by their strength under fire.
Purple & Lavender Roses
Purple roses were slammed the hardest by the intense heat. 'Night Owl', 'Twilight Zone', 'Blue for You', 'Ebb Tide', 'Outta the Blue', and 'Dr John Dickman' seemed to shatter violently under the intense pressure of 100+ degrees. In fact, 114 degrees caused 'Dr John Dickman' blooms to shrink to the size of a micromini, and some of the foliage turned black. 'Stainless Steel', a pale lavender hybrid tea, burned terribly. Interestingly, the light lavender rose 'Love Song' fared much better. The blooms did not fry even though this tree rose is in full afternoon sun. Neither did the miniature 'Scentsational', but it does get some afternoon shade protection under some larger hybrid tea roses.
Red & Red Blend Roses
Most of my red roses were hit hard too. The blooms of 'Black Magic' (a HT) and 'The Squire' (a shrub) were badly burned, but most of their foliage seemed fine. Only very young green foliage wilted and died. 'Let Freedom Ring' foliage burned but the blooms remained healthy. 'Lavaglut' didn’t seem to burn as bad as the others, but still there was some burning of the blooms. I was disappointed to see the red blend blooms of hybrid tea 'Dina Gee' shrunk to miniflora size, and they faded to nearly white.
Most of the white or white blend roses handled the heat pretty well. Miniflora 'Whirlaway' laughed at the heat and kept rolling along. Floribunda 'Fabulous!' survived surprisingly well, except where young tender stems were emerging. 'Moonstone' (pink & white blend) petals fried, although the leathery foliage remained unscathed.
Orange & Russet Roses
Orange and russet-colored roses produced mixed results. While 'Marmalade Skies' (an orange floribunda) sizzled in its hot location growing along the blacktop of the street, the miniature rose 'Cinnamon Girl' and hybrid tea 'Ring of Fire' did not seem to be affected by the heat. Even 'Touch of Class' held up well except the bloom size shrunk quite a bit. Russet-colored floribunda 'Cinco de Mayo' bloom clusters on my tree rose were perfectly fine during the heat wave.
Roses in containers were the hardest hit, especially because many of our containers are located on our front cement driveway, or our backyard cement pool decking. It’s even worse when roses are mature and rootbound, so they cook easily. I would like to say that containerized younger roses fared better, but Sparkle & Shine is barely a year old, grafted on a mystery rootstock and the blooms fried horribly in full-day sun at 114 degrees.
English Shrub Roses
English shrub roses had mixed results in this heat wave. The blooms of 'The Squire', 'Falstaff', 'Heathcliff' and 'Golden Celebration' were horribly devastated by the heat, but their foliage did not burn at all. Meanwhile 'Abraham Darby', 'Perdita', 'Radio Times', 'Molineux', and 'The Dark Lady' performed exceedingly well during the heatwave; their blooms and foliage did not burn at all.
Most of my nine polyanthas performed well in the heat even though they are in 10-gallon black plastic pots. They have morning shade but then full afternoon direct sun, which is the hottest part of the day. However, polyantha 'Lady Reading' was not happy being given extra water as her foliage became extremely chlorotic.
Old Garden Roses
What about the old garden roses? Well, 'Francis Dubreuil' fried completely even though it grows in afternoon shade. 'Yolande d’Aragon' and 'Baronne Prevost' frizzled badly because they are located up against a hot afternoon wall. 'Green Rose' of course had no burning problems as the green blooms are actually foliage. Oh, and marvelously humongous 'Paul Neyron' looked quite nice and fluffy at 105 degrees.
Miniature & Miniflora Roses
Many of our mini and miniflora roses are growing in 7, 10, 15, or 20-gallon containers, depending on their bush size. Their potting soil contains water-holding gel crystals at the base of each plant. We also have several microminis that grow in 1-gallon pots. Although most of our minis are growing on their own roots, some are grafted on 'Fortuniana' rootstock. Grafted roses grow faster and bigger, so they need a bigger pot size to perform well. Most of the minis and minifloras survived well during the heatwave. The roses that had more burning are growing in pots up against a southwest facing side of the house, or are located on cement, or those that have become rootbound.
Some of the single-petalled roses can survive and produce well even in temperatures over 100 degrees. 'Playgirl', 'Playboy', and 'Puanani', can still bloom nicely up to about 95 degrees, but sadly scald when over 100. Shrub roses 'The Imposter' and 'Paul Ecke, Jr' can handle quite a bit of heat, as can the minis 'Why Not', 'My Sunshine', and 'Halo Today'. All were nicely blooming at 114 degrees. However, the mauve single mini 'Lavender Spoon' was the first to scorch around 95 degrees.
I grow few climbing roses, but I will report on those I do grow. 'Shadow Dancer' was happy as a clam in the heat, even though growing up against the hot afternoon side of our house and then stretching over both sides of an archway. The large bloom clusters on 'Shadow Dancer' lasted for weeks even in 114 degrees. Amazingly bizarre! On the other hand, 'Night Owl' with its purple single-petalled blooms was not a happy camper even though it gets some afternoon shade. And it is the only rose in our garden that has been plagued with spider mites this year. Our new climbing rose 'Tropical Lightning' that is so young it’s still in a 5-gallon container waiting to be planted, didn’t seem to suffer any ill effects from the heat, and no foliage burning. However, that pot is growing in the shade at the base of climber 'Fourth of July', which by the way grows and blooms incredibly well in high heat.
What Caused the Rose Burning?
If you are wondering if the rose bloom and foliage burning might have been caused by spraying chemicals or feeding high nitrogen fertilizers, I can honestly say that my roses had not been fed or sprayed in over a month. So, the burning of my roses was obviously caused by extreme heat and sun, not by spray or fertilizer. Imagine how much worse my roses would have looked if I had been spraying or fertilizing during the heatwave. Oil-based sprays, which are more safely used in very cool weather, would have been even more detrimental and could have possibly killed the rose bushes during high temperatures.
Or you might ask if we forgot to water our roses. The quick answer is NO! Fortunately, our water company has lifted the water rationing. Partially, because there was a heavy snowfall in the Sierra Nevada Mountains this year so there is more water available. Also, I suspect that water cutbacks have been financially hurting the water company profits. So, during this heat wave we have been watering our in-ground roses every day at 4:30 am by automatic sprinklers for 12 minutes, and then at 6:30 pm we hand water container roses or other roses that are not covered by the sprinklers. Mind you, we are not wasting water by letting it run down the street or taking long showers nor doing other wasteful habits.
Tips for Preventing Rose Burning During Heatwaves
1. Do only light deadheading, and then just cut off the bloom, not stem or foliage.
2. Let the bushes grow tall so they can shade the bush.
3. Do not remove yellow leaves as they can help shade the canes and entire bush.
4. Let old foliage fall off naturally at their own pace.
5. Water the rose roots deeply before and after fertilizing, especially if applying dry granules.
6. Fertilize only lightly and occasionally during summer, e.g. slow-release types, or liquids at half strength.
7. Avoid high nitrogen fertilizers.
8. Water each bush deeply, not just on the surface.
9. Do not water during the hottest part of the day, only early morning, or early evening.
10. To help control spider mites, several times a week wash down the entire bush with a hose-end water wand, but only early morning or late afternoon before dark.
11. Apply several inches of mulch around each bush.
12. Do not spray chemicals on rose bushes in hot temperatures.
13. If you must spray for insects or disease, best to spray very early in the morning at sunrise, when it’s cool.
14. If spraying chemicals is absolutely necessary, be sure to water the rose roots the night before spraying.
15. Never spray oil-based products during the summer, as they are intended for winter dormancy.