You just brought your hibiscus (Hibiscus rosa-sinensis) indoors from its summer outside and now its leaves are turning yellow and dropping off, often massively. What’s wrong?
Well, first of all, no need to panic! This is a perfectly normal reaction for a hibiscus that has just suffered a major change in its growing conditions.
This kind of reaction is most common when you bring your hibiscus indoors late in the season, in late September, October or November.
If you had brought yours back indoors in early September, when you’re theoretically supposed to (see Time to Bring Your Houseplants Back In), you probably wouldn’t have seen such a strong reaction, because conditions indoors and out are essentially the same at that time of the year. As a result, the plant doesn’t react negatively to the rather benign transition and keeps its leaves.
But when it goes from cold nights (often below 50?F/10?C) and humid, buoyant outside air to hot, dry indoor conditions (because by now you’re heating your home and heating dries out the air), all the while undergoing a significant decrease in light (much less light reaches any plant indoors, even when you grow it in front of a sunny window), what a shock! The plant reacts by dropping many of its leaves… and often its flower buds too.
What to Do?
If you place your hibiscus in a sunny window at normal room temperatures and continue to water it thoroughly when its soil begins to dry, it will soon stop losing leaves and begin to produce new ones. Unfortunately, they’ll mostly appear at the ends of its branches, which can lead to a rather sparse appearance. That’s why it’s usually best to prune back your hibiscus harshly in late autumn, as this will stimulate denser growth.
And when I say “harshly”, I mean it. Your plant will probably look much better in the future if you call all its branches back to 4 to 6 inches (10 to 15 cm) in length.
Moreover, a late fall pruning will help stimulate next summer’s bloom, as hibiscuses usually start to bud up about 6 to 7 months after a severe pruning. In other words, yours will likely be full of buds when you put it outdoors next spring.
Don’t fertilize for the moment, however. Remember, your plant is recuperating from a severe shock and you shouldn’t overfeed weak plants. Plus you won’t want to stimulate rapid growth at this time of year, because days are short and getting shorter and, under the influence of short days, new shoots tend to stretch (etiolate). Instead, wait until March, when the plant’s new growth is well under way and days are lengthening significantly, before rewarding the plant with regular feedings.
Do note that hibiscus plants like high air humidity: if the air in your home is very dry, as it often is, the plant will be prone to spider mites. Here’s how to increase the atmospheric humidity in your home (High Humidity = Happy Houseplants) and how to treat spider mites (When Spider Mites Invade) if they do show up.
Good luck with your hibiscus!