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You’d be right to be concerned about your hibiscus leaves curling up. It’s a sign that something’s not quite right. What though?
It could be one of many things, however, with hibiscus, there’s certain things that are common knowledge among experienced gardeners that the novice growers aren’t aware of, until it’s too late.
Find the fix to stop the curling and help your hibiscus bloom!
Check Your Container and Potting Mix
Every species of hibiscus is best grown in containers. The reason is because they’re rarely year-round garden plants. They can’t tolerate cold winter temperatures so while you can grow them outdoors, you need to bring them indoors in the winter.
Growing in containers lets you do that easily without having to transplant them from ground soil to a potting mix then go through the motions of re-acclimatizing them.
Start them off in containers. Ideally, one that’s only slightly larger than the roots as hibiscus prefer mildly compacted roots.
When you need to size up your pot, only go up one size at a time. As in, if you have a 4” pot, go up to a 6” container. No bigger or the plant will start to struggle with the different growing conditions.
The potting mix you use needs to be well-draining. Like a lot of plants, hibiscus cannot cope with standing water. Suitable materials for potting up a hibiscus include: composted bark, perlite, coco coir, and peat moss.
Do not use garden soil as it doesn’t have the pore space to maintain a good amount of oxygen. Add water to garden soil in a container and you’re essentially turning off its oxygen supply.
Getting the Watering Frequency Right
Overwatering can be the cause of hibiscus leaves curling up. As hibiscus are tropical plants, they need a lot more water in the summer and then far less in the winter.
The hotter the weather (or indoor temperatures) the more water hibiscus plants drink. Cold weather watering means you only add water when the plant needs it. Where the problem sets in is when there’s a heavy spring shower or summer downpour.
Hibiscus does best when the growing conditions are kept similar throughout the year. Keep the conditions similar all-year, and it’ll drink much the same amount of water.
The sweet spots for indoors and out are 60°F (15°C) to 95°F (35°C). In the cooler weather, they shouldn’t be exposed to temperatures below 50°F (10°C) as that can cause damage such as stunted growth, leaf curl, and leaf drop.
They can tolerate higher temperatures but just because they can, doesn’t mean you should let them sit unshaded in the middle of a heatwave. In the summer, they may need some shade and during heavy showers, swap shade for shelter.
It’s another advantage of having them in containers. You can move them from an open spot in the garden to indoors, the shed, or temporarily place the plant under the shelter of your garden gazebo.
The important part is not to let a sudden heavy shower be the cause of overwatering. If it does happen, give the soil time to dry before adding water and definitely shelter it from showers in the meantime.
Also note that for tropical plants, more watering means increasing how often you water. Not the amount of water you give the plant. In extreme heat, water twice daily. Morning and evening. Not a heavy watering first thing to get it through the day.
Preventing Your Fertilizer from Killing Hibiscus
Hibiscus leaves curling up is also a sign of a mineral deficiency, but with hibiscus, you cannot add fertilizer on the hopes it’ll perk up because some fertilizers are toxic to certain species of plants.
Hibiscus is one of those fussy eaters because it can’t process phosphorous the same as other prolific garden bloomers. For that reason, the balanced fertilizers claiming to help spur plants into producing an abundance of blooms will be poisonous to a hibiscus.
The NPK you need is a medium level of nitrogen, low amount of phosphorous (critical) and a high amount of potash. There are various brands that use the medium-low-high formula, such as Grow More’s Bromeliad Tillandsia Food that uses a 17-8-22 combination, and the EZ-Gro Palm Fertilizer that uses 17-5-24.
The reason for the low potassium requirement for hibiscus plants is because it binds up other trace minerals in the potting mix, mainly iron.
For the minor, or trace elements that a fertilizer for hibiscus needs, look at the label (or description if you’re buying online) for the following: Iron (Fe), Copper (Cu) and it needs at least 3% Magnesium (Mg).
Not every fertilizer includes the same trace elements so check the label to make sure those three are in it. It can be a water-soluble fertilizer or in chelated form. Never in chloride form as you’d be dosing the plant in chlorine with every feed. Not good!
It’s not unusual for gardeners to use a fertilizer and supplement it with iron chelates at a different frequency, such as a weekly feed in the summer with a top up of iron chelate once monthly.
Iron deficiency can cause hibiscus leaves to curl and droop, but before you feed it iron chelate, consider if the fertilizer you’ve applied previously had too high an amount of phosphorous. No amount of iron can fix a phosphorous overdose.
Pests and Diseases that Result in Hibiscus Leaves Curling Up
Wilt is the most common sign that your plant has some type of infection. Hibiscus plants usually wilt when they’re sick. They stop drinking as much, the leaves start to curl up, droop and left to its own devices, it will get sicker. You need to nurse it back to health.
If you know your plant has the right potting mix, you’ve used the correct fertilizer and tried topping up with iron chelate and still notice the leaves aren’t perking up, check to see if the soil is wet, which is a sign that the plant’s stopped drinking and that is a sign of stress.
Usually heat stress, but it can be anything, including pests (covered below) which steal the nutrients you think you’re feeding the plants.
The few things to do to help a wilting hibiscus recover are:
- Move it into a shaded area, away from direct sunlight. Heat stress can cause hibiscus leaves to curl, shrivel and wilt.
- Mist the leaves to help it cool down and take some stress off the roots, but try your best to avoid spraying more water onto the soil. That needs to dry and being in the shade, that could take a while.
- Inspect the leaves for any that are yellow or yellowing and remove them. When any plant’s sick, it’s lacking its usual energy so for the little it does have, don’t make it waste it on leaves that are likely to fall off anyway. Take them away so that the plant can channel its energy into the leaves with the best chance of recovery.
Sap Sucking Pests That Starve Your Plant of Nutrients
One last check to do is on the underside of leaves, in particular, the leaves on your hibiscus plants that are curling. Look for any signs of insect damage.
Some of the ones that are prone to feasting on hibiscus are aphids, spider mites, and gnats. Some are so tiny that until there’s an infestation, they’re hard to see, but the signs aren’t always.
Most insects that damage hibiscus are the ones that feed on the sap of the leaves. Sometimes it might be the eggs/larvae. In most cases, they excrete honeydew, which usually results in a fungus coating the leaves, such as black sooty mold, leaf spot, or other fungal infection caused by pests.
You can get rid of most insects and fungal infections caused by them by either spraying the leaves with a hose, or treating the problem with neem oil or an insecticidal soap.
Hopefully, the only thing that’s not the culprit of your hibiscus leaves curling up is too much phosphorous. That’s the only thing that’s hard to recover from. Everything else is fixable.