I got a post from Robin asking about indoor hibiscus that turn brown and die in February. Well, it could be a few things: not enough light, too much water or fertilizer, too cold, pests. The best choices are too much water and pests.
Hibiscus like to be in a rest period during the winter and should only be watered to keep the soil from drying out, not soaked. If it gets too much water, it goes through what is called physiological wilt. The roots essentially suffocate because the soil is so wet that the root system can’t get any air. Let the plant dry out, and if it isn’t too late, it should releaf. You can do the nail check by scraping a stem with your thumbnail and see if it is green. If it is yellowish or brown, you might as well start over. Never let the plant sit in excess water in the saucer, always pour that off. Let the soil dry up in between waterings to keep the plant protected from root rot. And use warm water (between 95 and 102 degrees F) during the winter months. Otherwise it is too much of a shock to the plants. Just use your hand to make sure the water doesn’t get too hot.
The other thing that kept popping up in my reading involved pests, all of which seemed to cause the leaves to dry up and fall off in February or March.
If you are bringing the hibiscus in from the outside, always make sure that you get all the bugs off. You can use a systemic insecticide during the summer, carefully following the label directions. Repeat the application about seven to ten days before bringing the plant inside in the fall. In some instances the problem may be scale which can cause black bumps to cover the stem.
The most common pest in the dry indoor environment is the Spider mite. You don’t have to pick all the pests off. Instead get some horticultural oil that won’t damage the plant. You can also give the plant a shower every other day or so, or at least once a week. Cover the top of the pot with foil or something secure to keep the extra water from leaching the soil. Pour fresh, clean water over the plants. Not only can it dislodge your pesky houseguests, it will also have the benefit of “dusting” your plants and keeping them shiny and healthy.
All hibiscus will have yellow leaves at times. If you only have a few, it means those leaves are getting old and are ready to fall off and be replaced by new ones. If there are many yellow leaves, the plant is under stress. Under-watering, pest invasions (especially spider mites) and drastic changes in environment (including being brought inside in the fall) are common causes.
If you have bud drop, it is often the result of drought or a severe pest attack. Another cause can be that if your hibiscus is in bud, it should not be turned. If your plant has buds and you want to turn it for more even growth, only turn it a quarter turn each time.
Tropical hibiscus, as the name implies, are a tropical plant and like warm temperatures. They prefer moderate heat and like bright light. If you want the plant to continue to bloom, it must have a few hours of direct sunlight, so place it in a South or West facing window. Watch out for cold drafts that can give hibiscus frostbite. If you don’t think your natural light is bright enough, you can add fluorescent lights to help the hibiscus.
For fertilizing, you can let the plant rest a bit during the winter or you can continue to feed it, if you want to keep it flowering. Don’t feed it when the plant is dried out as it may damage the roots. Rehydrate the soil first by putting the pot in a bucket or water or a sink filled with water. Leave it in the water for about 30 minutes and then return it to the planter it was in. Now you may fertilize the plant. If you use a water soluble formula, you can fertilize every time you water. Choose a fertilizer with low phosphorous (N) value. A 20-5-20 is a good choice for the plants. If you have too much phosphorous you will get a lot of nice leaves, but not too many flowers.
If you need to re-pot hibiscus, February and March are good months to do it in, especially if the roots are poking out of the bottom of the pot through the drainage holes. Loosen the roots properly and maybe even cut them off. Healthy roots are white to tan in color, crisp and plump. Completely cut off any dark brown or soft roots. And if there are too many roots, you should cut a few away. Replant in one size larger pot than it was in, using a loamy, but not too heavy a soil. You can use a good potting soil with some compost added in. Don’t use a soil made with mainly fine peat as that tends to compact in the pots and will not let the roots breathe.
The best time to prune your hibiscus is August through October, but some spring pruning can still give some good results. Since hibiscus flower on new shoots, this can help stimulate budding as well as clean up the plant. Completely remove weak growth or branches that are growing sideways and never prune off more than a 1/3 of the mass.
Good luck with your indoor hibiscus. Keep it warm and hydrated and it should reward you with beautiful color through the winter.