“How warm do I have to keep my house for a tropical hibiscus? I live in Maine, and it gets quite chilly!” Question from Valerie of East Andover, Maine
Answer: Your tropical hibiscus (Hibiscus rosa-sinensis) will grow best in temperatures between 55ᵒ and 85ᵒ Fahrenheit. If temperatures drop below 50ᵒ F, it will require some protection. Inversely, temperatures above 100ᵒ will cause it high stress, but that’s certainly not a problem you will have. Tropical hibiscus also grows best with a higher level of ambient humidity.
Just give you plant warmth above 55ᵒ, good humidity, and it should grow well until your spring days grow warmer. Also, be sure not to overwater hibiscus growing at cooler temperatures. Less water is needed under cooler growing conditions, and too much water can cause root rot.
“When is the best time to trim tropical Hibiscus?” Question from Jane of Tampa, Florida
Answer: You can prune these evergreen tropicals at any time to manage plant size, encourage denser growth, and induce more flowering, but pruning is best done in late winter when they are blooming very little.
These tropical Chinese shrubs flower on new wood, and pruning encourages the development of new wood, so it’s a great way to get them to bloom more. Here are five good hibiscus-pruning tips.
Late winter is generally a good time to prune, but wait until the weather is sure to be consistently warm.
Use clean, sharp pruning shears.
Make 1/4-inch angled cuts above the leaf joints (the angle’s point should be towards the leaf joint).
Remove sprawling, unruly branches that ruin the plant’s bushy shape.
Refrain from pruning again until the following year unless your shrubs become too overgrown.
Just be sure to refrain from pruning when your hibiscus are in full flower.
“What are the reasons leaves drop from [tropical] hibiscus?” Question from Brenda of Miami, Florida
Answer: Tropical hibiscus (Hibiscusrosa–sinensis) are lovely shrubs when they are healthy and happy, but they look so dismal when they’re in poor shape–especially when they start dropping their leaves. There are LOTS of problems that can lead to leaf drop. Some of these depend on whether your plants are potted or in the ground.
Here are several common leaf-drop causes in potted hibiscus.
Bound Roots – This means the plant has overgrown its pot and needs an upgrade. In this situation, the roots cannot access proper water and nutrients, and plants begin to decline. Poor growth, wilting, and leaf drop are just a few of the signs. Watch the video below to learn how to identify and repot pot-bound plants.
Overwatering or Underwatering – Watering too little or too liberally can stress plants out. Tropical hibiscus need good soil moisture, but they can’t stand waterlogged soil. Irrigate when the top inch or two of the potting mix feels dry, and then water the pot thoroughly until the plant’s saucer is full. Your soil must also drain well while holding lots of moisture (Black Gold Moisture Supreme Container Mix is a good choice).
Change of Scenery – If you recently moved your hibiscus to a shadier, windier, or indoor location, changes like this can cause stress and subsequent leaf drop. Give them good care, and they will snap out of it.
Spider Mites – These tiny, destructive pests are nearly impossible to see but cause discoloration of leaves and eventual leaf drop. If you have them, you might also see little webs on the leaves and tender stems of infested plants. To determine if you have mites, take a clean piece of white paper, hold it beneath the leaves, then tap the leaves onto the paper. If you have mites, lots of tiny specs will fall and eventually, they will start crawling around. These are spider mites! (Click here for everything you need to know about getting rid of these pests.)
Poor Soil and Lack of Fertilizer – Be sure to refresh your plant’s soil every two years, and provide it with ample fertilizer for lush growth and flowering (follow manufacturer’s recommendations).
If your plants are growing in the ground, sharp temperature changes and high winds can cause leaf drop as can pest and disease problems. Considering that you live in Miami, I doubt that temperature changes are an issue.
Please let me know if any of these solutions help!