What's the problem with our hibiscus?

last year

last modified: last year

We are wondering why our two hibiscus plants developed these totally white spots, and some of the young leaves are curled up. No bugs that I can see. We are in zone 5, typically these two hibiscus plants spend all winter indoors and summers outdoors. I have always acclimatised them slowly for outdoors, this year as well. We started about three weeks ago, increasing hours every day, and brought them back indoors when the temps were forecast to go below 10 degrees C. At times they were exposed to very strong winds.... was able to rescue them just in time from a twister a week ago, but they had these symptoms already. I have seen them turn slightly pale before when first bringing them outdoors, but then they would normalise over the summer. Never saw this. I have been fertilising them with the same fertilizer they always got. I know they need fresh soil, but they started blooming earlier than expected, so I thought I'd wait till there is a lull in the blooming phase.

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tapla (mid-Michigan, USDA z5b-6a)

last year

last modified: last year

Hibiscus blooms on new wood, so you'll still have blooms this year if you repot, but I would stop using the 15-30-10 and the seaweed emulsion. I checked, and you can get Dyna-gro products in CA. I would suggest that you adopt Foliage-Pro 9-3-6 as your 'go to' fertilizer for potted plants. It has ALL nutrients essential to normal growth in a single container, in a ratio that will make almost everything you might grow happy, except hibiscus, an outlier with it's intolerance of anything but low levels of phosphorous and the fact it needs more potassium than nitrogen. Fortunately, that's easy to fix by using the Foliage Pro 9-3-6 and and another Dyna-Gro product called ProTeKt 0-0-3, which will satisfy the plant's need for more potassium than the average plant. In summer, and as long as you're flushing the soil as you water, you can use the Foliage-Pro and the ProTeKt on alternating weeks. Example: FP 9-3-6 one weekend, ProTeKt 0-0-3 the next weekend, repeat.

I'm going to show you some images of what a repot looks like, to set your mind at ease when it comes time to start working on the roots. The first step would be sawing the bottom half of the root mass off with a pruning saw.

3 images of a young Japanese Maple:

Boxwood, 3 images:

Ficus benjamina with some extremely heavy roots removed - 3 images:

If you can find pine bark in an appropriate size, you could easily make your own soil. It would be much less expensive than commercially prepared media and much better. This is what I use - objects meant to provide viewers with some sense of relative size of the particles:

If you're not interested in making your own medium, I suggest you use a wick to help you drain away excess water:

Compare figure E to A to see how much excess water a wick can remove. Also, see how tipping a pot after watering (fig B) removes excess water, and how adding ballast to the bottom of the pot (Fig D) also limits how much excess water a planting can hold. Simple science can passively make your job as a grower much easier when there is no alternative to using a water-retentive medium.

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Comments (7)

tapla (mid-Michigan, USDA z5b-6a)
last year
Hibiscus has a very vigorous root system, so they need a full repot every year if you want to maintain them at a high level of vitality. A full repot is much more involved than simply potting up, which ensures root congestion in the center of the root/ soil mass will be a perpetual limitation, or at a minimum, a limitation until a pair of hands gets into the roots and corrects the congestion and problem roots, problem roots being circling/ girdling/ crossing/ j-hooked roots, roots growing straight up or down, and roots growing back toward the central axis [middle of the root mass]. The person repotting should focus on bare-rooting the plant and removing large roots not directly attached to the base of the plant. Large roots serve primarily as plumbing, while fine roots do all the plant's heavy lifting when it comes to sustaining the plant. If you prune it hard, you can easily remove 2/3 of the root mass.

Some might suggest that sunburn is responsible for the bleached parts on the foliage, but I don't think it is sunburn, which usually involves the thicker part of the leaf and not leaf margins except in severe cases, in which the entire leaf would be involved. The damage looks more like over-watering or a high level of dissolved solids (salts) from tapwater and/or fertilizer solution in the soil.

I would forget about losing a few blooms, prune the plant hard, and repot the plant. If you don't, and as the root congestion increases, you'll see loss of most foliage proximal (closer to the trunk) to the tips of the branches (apices) where growth occurs, leaving your plant with tufts of foliage near the tips of the branches and largely bare other than the leaves there.

If you're not fertilizing, you should be. Hibiscus likes very little phosphorous and lots of potassium. So a fertilizers with a RATIO (different than NPK %s) somewhere around 3-1-5 would be most suitable. I use a 3:1:2 ratio fertilizer (Foliage-Pro 9-3-6) and provide the extra potassium hibiscus craves by supplementing the fertilizer with ProTeKt 0-0-3 which also provides silicon, which the plant will appreciate. Never use a bloom booster type fertilizer for containerized hibiscus, and it should not be used on plants in the ground unless a phosphorous deficiency has been identified by way of a soil test.

Finally, your plant would appreciate being over-wintered in a cool, dark place and kept very but not completely dry. It will wake in the spring with plenty of energy for a spring push, not tired from pushing long lanky growth that needs to be removed anyway. The lanky growth represents lost energy that, if the plant was kept in a consequential dormancy, could/would have gone toward new and tight/ compact spring growth.

I'm not sure where you live, but I'm betting it's somewhere where you can repot now with no problem. If you share where you're located, I can tell you for sure ...... if you plan on putting what I suggest into practice.

Al
doriswk
Original Author
last year
last modified: last year
Hello tapla, I truly appreciate your very detailed info ! We are in zone 5, near Toronto, Ontario. Warm enough to re-pot , I just have to let go of my vision of lovely flowering hibiscus this summer.... I am guilty of not having re-potted them for a couple of years now.

Can't remember, is potting soil for tropical flowers recommended, or can I use regular Pro mix potting soil, with some added coconut chips ?

How hard should I prune them ? Should I leave some leaves, or cut all leaves off ? Many are damaged anyways...

Don't think this is a matter of over watering, they sometimes flagged before I watered them, I imagine there is probably not much soil but lots of roots.

I have had these plants for perhaps 18 - 20 years and always ( except in winter) been fertilizing them with Plant Prod 15/30/15, they seemed to do O.K. with it, and we were even using chlorinated city water. But we moved and for the past 6 month we have been on well water, no chlorine but I think its quite hard, with lots of calcium. Maybe the hibiscus don't like it together with the 15/30/15 fertilizer.. For the last three months I have been rotating between liquid seaweed fertilizer and the 15/30/15.

I trust your expertise I will follow your advice and re-pot them as soon as I have fresh soil etc. in place.
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I'm assuming it's in a container ...... ? Probably very root bound - major symptom is shedding of interior foliage, thus the yellowing as the plant prepares to shed foliage. Check for mites - it looks distinctly possible, from the picture. If it's in a pot, saw the bottom 1/2 - 2/3 of the root mass off, bare root the remainder of the root mass, prune out the largest 1/3 of the remaining roots & repot. Make sure the roots remain moist for the entire time you work on them. The root pruning will have a CONSIDERABLE rejuvenating effect on the plant, the physiological reason for which I'll explain if you're curious. Use a fertilizer with a 2:1:2 ratio, or a 3:1:2 ratio (like MG 24-8-16 or 12-4-8) and add a little potash to the fertilizer solution each time you fertilize. DON'T use a fertilizer that supplies more P (middle number) than N or K. If you don't understand the difference between your fertilizer's NPK %s and its ratio, ask, and I'll explain. Al
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May, are you sure the fly's are coming from the hibiscus and not another plant? If they are coming from the hibiscus, when you repot use new soil. Find a good well-draining mix. Or make your own w/all purpose, peat, and sand. Just a couple cups of sand, depending on the size pot..What size it the hib in now? As longer days approach, and hib gets better light, leaf drop should stop. Are you planning on taking the hib outdoors in summer? They do great outdoors if you have access to an area. Toni
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It's not strange at all, even if it might seem so to some who aren't aware of how severe are the limitations that can be imposed by root congestion. Too, I didn't go all anthropomorphic and suggest the plant wanted to strangle itself. Given any plant, the roots of which are tangled and wrapped around each other such as the conditions that are prevalent in plants left to become badly root bound - encircling/girdling/crossing, j-hooked roots, roots growing straight up or straight down, roots growing back toward the center of the root mass, are all part of the condition. When you put that plant in the landscape, the problems aren't "solved", and they don't go away w/o intervention. They remain and are limiting for whatever length of time it takes for the plant to give up the ghost. This plant, though not hibiscus, would never do well if I just planted it out in the landscape with the root mass intact.It would falter and die within a few years because the roots would cut off the flow of water/nutrients/bio-compounds to the top and carbohydrates + other bio-compounds to the roots. The same plant (below), with the roots properly attended to, has a much longer life expectancy, thanks to the root work. Same deal here and here:Al
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ken_adrian Adrian MI cold Z5
last year
Can't remember, is potting soil for tropical flowers recommended, or can I use regular Pro mix potting soil, with some added coconut chips ?

==>>>

it really doesnt matter what you use.. as long as you 'LEARN' HOW TO USE THE NEW STUFF ....

start with the presumption that all prior watering systems are void.. and learn how to water with the new stuff.. and you should be all set ..

other than that.. as always.. what al said...

ken
doriswk thanked ken_adrian Adrian MI cold Z5
ken_adrian Adrian MI cold Z5
last year
oops... lol

i suspect some wind damage ... since you hardened them off properly ...

look to the new growth for what is currently going on ... and that growth mostly looks ok ...

and.. full bright shade for at least a month... after the repot ... no direct sun at all.. until we are sure the roots have settled down and are pumping water ....

ken
doriswk
Original Author
last year
last modified: last year
Yes Ken, I am sure there is wind damage. Unfortunately we have a lot of wind with occasionally very strong wind blowing around our house and they'll be exposed to it no matter where we put them, except on the North/ East facing side where the azaleas are and there is not much sun at all. But maybe that should be their spot for a while ?

Ken, did you see, some of the new growth are curled up leaves.

Tapla, could you please clarify if you suggest to use Foliage-Pro 9-3-6 as a 'go to' fertilizer for all potted plants incl. the hibiscus, but give it to the hibiscus only every second week, alternating with ProTeKt 0-0-3 ?

.

Again, how hard should I prune them ?
tapla (mid-Michigan, USDA z5b-6a)
last year
Leave them in full sun, even if some leaves burn.

"..... could you please clarify if you suggest to use Foliage-Pro 9-3-6 as a 'go to' fertilizer for all potted plants incl. the hibiscus, but give it to the hibiscus only every second week, alternating with ProTeKt 0-0-3?"

From above: I would suggest that you adopt Foliage-Pro 9-3-6 as your 'go to' fertilizer for potted plants. It has ALL nutrients essential to normal growth in a single container, in a ratio that will make almost everything you might grow happy, except hibiscus, an outlier with it's intolerance of anything but low levels of phosphorous and the fact it needs more potassium than nitrogen. Fortunately, that's easy to fix by using the Foliage Pro 9-3-6 and and another Dyna-Gro product called ProTeKt 0-0-3, which will satisfy the plant's need for more potassium than the average plant. In summer, and as long as you're flushing the soil as you water, you can use the Foliage-Pro and the ProTeKt on alternating weeks. Example: FP 9-3-6 one weekend, ProTeKt 0-0-3 the next weekend, then repeat.

Al

What's the problem with our hibiscus?

tapla (mid-Michigan, USDA z5b-6a)

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tapla (mid-Michigan, USDA z5b-6a)

doriswk
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ken_adrian Adrian MI cold Z5

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What's the problem with our hibiscus?

tapla (mid-Michigan, USDA z5b-6a)

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tapla (mid-Michigan, USDA z5b-6a)

doriswkOriginal Author

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ken_adrian Adrian MI cold Z5

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