Tips for Hibiscus in Extreme Summer Heat
August heat is here! Like humans, hibiscus struggle to look their best at the peak of summer heat in places where temperatures stay at or above 95°F (35°C). They need a little help to survive the heat and keep blooming and growing. We can't change August temperatures, but we can make some small changes that can make a big difference for our hibiscus.
Split Your Watering between Morning and Evening
In places where heat is extreme, hibiscus need to be watered lightly twice per day - once in the morning and once in the afternoon or evening. Research has shown that tropical plants of all kinds do better when their daily dose of water is split into two half doses so they stay more evenly hydrated. If you water only once in the morning, on very hot days the hibiscus can reach the pre-wilt stage by evening. You can't see any wilt yet, but the hibiscus are stressed and can be set back if this happens often. One of the first consequences of this type of stress is fewer buds and flowers. It's not a matter of using MORE water - a particularly important fact in places like California. Just splitting the SAME amount of water you have always used in the morning will give your plants more benefit. For example, if you run your drip system for 6 minutes each morning, then switch to 3 minutes twice a day, morning and afternoon. Try it! You'll see how well it works!
Use a Drip System
A drip system is the by far the best, easiest, and most water-wise way to care for hibiscus. You adust your timers for each season - once a day watering in spring and fall, twice a day in summer, and once or twice a week in the winter, depending on how much rain you get. In areas of extreme heat, unless you want to spend your summer months holding a garden hose, a drip system is really almost a necessity. Drip systems are not very hard to build. We have instructions on our website that anyone can follow: How to Build a Drip Watering System. There are many other websites that provide information on building them too, plus any landscape company can build one for you for much less than the cost of traditional sprinkler systems.
Shower Your Plants in Extreme Heat Waves
When temperatures soar above 95°F (35°C), a quick shower during the hottest part of the day is one of the best ways to quickly cool your hibiscus plants. Just hose them off quickly and let the water stand on them and slowly evaporate. Use a Bugblaster or a garden hose with a soft sprayer nozzle to get up under all the leaves and thoroughly wet them. This both cools and hyrates the plants, which will help prevent heat stress. Once a week, take the time to do a thorough showering job, spraying up under all the branches, leaves, stems and all around the trunks, as a pest prevention strategy which will keep away white flies, aphids, and spider mites.
Double-Pot to Protect Overheating of Roots
Exposing plant pots to direct sunlight can cause overheating of the root ball. One technique for preventing this is to double-pot your hibiscus. Place the moisture-retaining plastic pot inside a larger, well-draining ceramic pot that will provide cool shade for the roots. In addition to cooling the roots, ceramic pots usually look prettier, plus they are heavier and help keep large plants weighted down, and standing up. We've all had the experience of hibiscus plants tipping over easily in their lightweight plastic pots. Heavier ceramic "sleeve" pots help provide the anchoring and cooling that the earth provides for hibiscus that are planted in the ground.
Never Prune in Extreme Summer Heat!
At this time of year our hibiscus can start to grow wild and crazy, with long, stray branches. But if you live in a place with extreme heat, resist the temptation to prune your plants! Any kind of cutting or pruning creates extra stress and every cut allows moisture to escape and pathogens to enter the plant. So wait until the temperatures drop down into a more comfortable range in the fall before you prune and shape your plants. This goes for root-pruning too. Extreme heat adds enough stress to our plants, so we need to be very careful not to add any more.
Find or Create Some Shade:
If your August temperatures are mostly in the low 90's F (low 30's C), you don't need to worry about giving them extra shade. Hibiscus can get used to these temperatures and will be fine as long as you provide plenty of water and good nutrition. Your flowers may be a little smaller and some buds may fall off without blooming during the hottest months, but otherwise, your hibiscus plants will be fine. But if your temperatures are consistently around 95°F (37°C), a little bit of shade will make a big difference in both the health of the plants and the quality and quantity of the blooms.
If your hibiscus are in pots, shift them to the north or east side of your house. Or put them under a tree, or next to a wall, larger shrubs, or anything that will give them partial relief from all-day, relentless sun. Porches or covered patios are ideal for hibiscus in very hot climates, but even just a couple of hours relief from blistering sun is better than no relief. Every little bit of shade gives the hibiscus plant a chance to cool down and recover from the kind of stress the burning sun causes.
If your plants are in the ground, you may want to try to bring the shade to them. It doesn't take much to help. A standing umbrella, a piece of shade cloth or parachute cloth strung up between some trees, anything at all that breaks up the sun will provide some help for your hibiscus. Make it artistic if you like! String up several pieces of colorful cloth criss-cross across your hibiscus garden. Shade doesn't have to look like institutional shade cloth. It can be anything that crosses between your hibiscus and the hottest sun and blocks out even a little bit of the sun. Of course, you can use greenhouse-grade shade cloth if you like. Whatever suits your fancy is fine, and any shade is better than no shade in places where heat is extreme.
We grow hibiscus in temperatures up to 110°F using these techniques, so we know they work! It takes some patience and diligence to get everything right, but in the end, you should have happy, healthy, blooming hibiscus all through the summer months.
Hibiscus Summer Blues
Hey Man! I'm Just Trying to Cool Off!
Hibiscus sometimes need forgiveness, and extreme summer heat is one of those times. Some weird things that your hibiscus do are just normal reactions to extreme heat. You need to know what these natural reactions to heat are. There is nothing worse than overtreating your plant with every possible pest control product when the plant is at its most stressed! We get email frequently from customers at this time of year describing the symptoms below, and saying they have already tried "everything" - harsh soap that strips the wax off the leaves of the plants, heavy oils that make it much harder for the plants to breathe, multiple pesticides that add more stress.... Yikes! Stop! Read! Make sure you know the natural signs of heat stress!
Leaves Look Cupped and Bumpy
Leaves can cup in extreme heat & humidity
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Leaf cupping and bumping on hibiscus can sometimes happen in very high humidity and heat combined. This is how it works: In a normal healthy leaf, the outside edges grow faster so the leaf can get bigger and bigger around. The inside cells grow more slowly, so the inside of the round leaf will maintain the correct size ratio with the outside. Leaves naturally grow each cell at the proper rate to maintain the correct leaf size and shape for their plant variety.
In extreme high heat, the outside cells feel the most heat, since they are more exposed. They respond to this stress by slowing down their growth to preserve energy and to prevent burning of the tender edges. Slowing down can also have the effect of thickening the edges and curling them, which helps the leaf edge survive burning sun and heat. This smaller outer edge makes the leaf grow in a cupped shape. It does not hurt the plant at all though. It's a coping strategy to protect the tender leaf edges from severe burning. It's a natural reaction to a stressful situation, and as soon as the heat stress is gone, the leaves will start growing normally again.
Leaves can get bumpy in extreme heat & humidity
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If high heat is coupled with extremely high humidity, as in a greenhouse, closed-in room, or extremely humid tropical location, the inside leaf cells may start growing faster. In extreme heat, air can hold much more water than it can in lower temperatures. So the air becomes saturated and heavy with water. All this water in the air makes it hard for the leaf cells to transpire, release oxygen into the air, and suck in carbon dioxide from the air. The cells buried in the middle of the leaf have less surface area touching the air, so they have the most difficulty transpiring in extreme humidity. They respond by growing faster than usual, making bumps and bubbles inside the leaf where the cells are stretching out to reach more air. This too is a harmless, normal reaction to extreme heat and humidity. As soon as the humidity drops back into a normal range, the leaves return to their normal, smooth growth pattern.
The solution for both these problems is to try to reduce the heat and/or humidity. The tips above will help reduce heat. To reduce humidity, try to move your hibiscus into a more breezy location or try to provide some kind of air flow for your hibiscus if you can't move them. More air flowing past the leaves helps push away the water in the air, and makes more carbon dioxide move across the surface of the leaf. Plus, the air movement itself helps create a bit of suction to push and pull air into and out of the leaves, as well as cooling the leaves. If your hibiscus are inside a greenhouse or house, move them outside into some fresh air if you can. If you can't move them, then trying running a fan to blow air on them. Anything that increases airflow will make leaves return to normal growth.
Buds Fall Off Before They Bloom
If your buds fall off before they bloom, first and always treat for Thrips. Thrips are everywhere, all over the planet, and summer is their time to fly into your garden and lay eggs in your flower buds. You may never be able to see the bugs or even the damage to your flowers. They may infest your hibiscus so quickly that the first sign you see is severe bud drop.
But after you have treated for thrips several times and most of your hibiscus have started blooming normally again, you may still see some buds fall off your hibiscus. This is especially true of the buds of doubles. The double flowers have many, many more petals than the single flowers, and it takes each bud a very long time to build all those petals. In extreme heat, the sun can actually cook the large buds of doubles before they get a chance to bloom. Buds of singles can cook sometimes too. You will see this most often in buds that are in the sunniest spots, such as a stray branch that reaches way out into full sun, or a bush that has a full southern exposure.
Providing shade and extra hydration with showers will help the buds stay cooler. If your heat is very, very extreme every summer, you may need to find permanent shadier places to grow your hibiscus. If your hibiscus are caught in an unusual heat wave, then just wait it out. The bud loss will end when the temperatures drop back into the normal range.
Flowers are Small and Pale or Weird Colors
'Orange Appaloosa' develops bright,
yellow spots in high heat.
The yellow caretenoids protect
the flower in hot sun.
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One solution that hibiscus have for the "cooked" bud problem is simply to bloom sooner. Many single hibiscus varieties use this adaptation naturally. The result is, your flowers will be smaller. Not to worry! This is just a normal reaction to high heat. The flowers will get back to their normal large size as soon as the weather cools down. It is much better to bloom with smaller flowers than for the buds to stay on the plant too long, get cooked and fall off, right?
Pigments are another part of bud development, and different hibiscus varieties have different reactions to pigment development in extreme heat. When the buds start to feel "cooked," some hibiscus churn out protective pigments, like the super tough orange, red, and yellow caretenoids. This is what makes a solid red or orange hibiscus develop big yellow spots and splashes in summer heat. Or a soft peachy-colored hibiscus can turn vivid red or orange in high heat. These tough pigments help shade, cool, and protect the flower cells from the sun, and these end up being the hibiscus those of us in the hottest places tend to love the most.
A small, pale, weird 'Carrot Cake' in extreme heat,
usually large, bright orange and brown.
Its pigments are anthocyanins
that burn off in hot sun.
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Other hibiscus varieties have more fragile pigments, like the anthocyanins of blues, browns, and some types of reds and pinks. These pigments get burned away by hot sun. In the highest heat they sometimes burn away before the bud can open. These are the hibiscus that bloom with very pale flowers in extreme heat. Some varieties with the most fragile pigments can even bloom with almost completely white flowers. The sun has burned away almost all the pigments! If you have a hibiscus that does this in hot sun, try to move it to a location that provides more shade. Blues and browns generally have the least tolerance for full, hot sun, and in any hot place, they will always need some shade.
Be Patient! Wait for Cooler Weather!
If you buy a new hibiscus in the middle of the most extreme summer heat, the act of moving the hibiscus to your location, combined with the extreme heat, will more than likely produce at least some of these natural responses to heat stress. Don't panic. If your flowers aren't what you expected, just give your hibiscus the best possible care, and wait for the weather to cool down a bit. Little by little your hibiscus will acclimate to its new home, adjust to the heat, and then start showing you its most glorious beauty. Extreme summer heat demands patience above all, for all living creatures, including our favorite flowers!
Seedling of the Month...
In search of a flower that looks like 'Typhoon'
with all the perfection of a 'Simple Pleasures' plant
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Meet our newest seedling of the month, the child of 'Typhoon' and 'Simple Pleasures.' "OK," you say, "We've seen flowers like this before. What's so special about it?" That, our friends, is THE QUESTION. So many hibiscus flowers look so much alike. What's the difference? They all look the same? Why keep hybridizing new ones????
The answer is, we're in search of the PERFECT hibiscus hybrid. Well, maybe not "perfect," since it's doubtful that there is such a thing. But as close to perfect as we can get. For each gorgeous hibiscus flower, we want a lusher plant, full of branches, with full lush leaves, that's easier to grow, that blooms constantly, that resists pests, that tolerates heat, that tolerates cold, with tough pigments that don't fade in sun, and (yes, there's still more!).... that propagates easily so we can grow the darn thing in large enough quantities that people can actually get one before they sell out!
Hibiscus are the easiest plants in the world to hybridize. Brush a bit of pollen from one flower onto another, et voilà! You have a new variety. But hibiscus are one of the hardest plants in the world to get RIGHT. Some very beautiful flowers bloom on bare stick bushes, or branches so weak they can't hold the flower up, or one single stem that grows straight up and refuses to branch. Or maybe the bush is pretty good, but sadly the hibiscus only blooms once a month on the third Sunday! Or maybe everything is perfect, but it's nearly impossible to propagate new plants from it, and when the new ones start growing, they don't have the vigor of the parent plant. There are a million and one things to frustrate hibiscus hybridizers, and we find them all!
Our new seedling is only 1/4 'Typhoon'
But the flower is very similar!
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So what is so special about this new seedling? We don't know yet! We don't even know if it will be special. We chose it to illustrate what our hybridizing is about.
The mother of this seedling is 'Typhoon' - the offspring of 'Moonstruck' and 'Simple Pleasures.' Both these grandparents are super bloomers with large flowers. 'Moonstruck' has the flaw of flowers fading in the sun. 'Simple Pleasures' is nearly flawless, but the flowers are only the large 7-9" size instead of the giant 8-10" size of 'Moonstruck.' So we crossed these two varieties in the hopes of getting a giant bloom like 'Moonstruck' without the fading flaw, and with the spectacular bush of 'Simple Pleasures.' We got 'Typhoon,' a gorgeous hibiscus that took us part way to our destination. The bush of 'Typhoon' is good, better than 'Moonstruck,' but not as good as 'Simple Pleasures.' The flower of 'Typhoon' has more color than 'Moonstruck' but does still fade some, unlike 'Simple Pleasures.' Plus 'Typhoon' is harder to propagate, like 'Moonstruck,' instead of easier to propagate, like 'Simple Pleasures.'
Our new seedling is 3/4 'Simple Pleasures'
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So..... still in search of a hibiscus flower that looks like 'Typhoon' and has the near-perfect qualities of 'Simple Pleasures,' we crossed 'Typhoon' back with 'Simple Pleasures' again. This new seedling is the result of that cross. It's lineage is 3/4 'Simple Pleasures' and 1/4 'Moonstruck.' You would expect that our seedling's flower would look a lot more like 'Simple Pleasures.' But no! It doesn't! It looks like a better, more deeply pigmented 'Typhoon' flower that fades less! BUT the bush looks more like 'Simple Pleasures!' Mission accomplished!
.... Or so we hope. We have a lot more watching and testing to do with this new seedling. In the end, we may have to go back to the drawing board. But because we spend our days, nights, and everything in between working on these thorny hibiscus hybridizing problems, we thought it might be fun for you to see the inner workings of one of our thousands of multi-generational crosses. Will we ever grow a perfect hibiscus? Probably not! But it won't be for lack of trying.
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