I have two hibiscus trees I brought in for the winter. They are in my foyer where they get light from the window above. One is fine, but the other has a dirt-like or sand-like sticky substance on the leaves and flowers, both on top and underneath. What do I do, if anything? Also, how often should I water?
The Gardener’s Answer
This is the time of year when in some cases the plants we brought inside to over-winter start letting us know that they are not happy. Any time we move plants from one environment to another it causes stress on them. We simply can’t provide adequate sunlight, temperature, or humidity indoors. Too much moisture can also cause plant stress, and when plants are stressed, they are more susceptible to insect and disease issues.
Tropical hibiscus are no exception, and from what you have described it sounds like aphids have been feeding on your plant. Aphids are little insects that have piercing/sucking mouth parts. As they feed on the plant they also secrete a sticky substance known as honeydew. This will drip on the rest of the plant and on the floor around your plant. Black sooty mold can also develop on the honeydew.
Depending on how heavy the infestation is, you can sometimes just wipe them off, but usually a combination of a granular systemic and foliar spray is your best bet. Aphids are very efficient at reproducing, so it is best to treat your plant as soon as you notice them. Make sure to purchase products that are labeled for aphids and safe for hibiscus.
As for watering, less is better during the winter months. Do not let the soil completely dry out, but it should never be sopping wet either. Your watering routine will depend on the temperature and humidity of your home, but every 7-12 days should be sufficient. Always check the soil for moisture before adding any more. If the soil is dry to the touch a couple of inches down, then go ahead and water, but otherwise it is not necessary. When you take them back outside in the spring, move them to a shady spot and slowly acclimate them to the full sun