Hibiscus (Hibiscus spp.) flowers bring bring tropical scenes to mind, but you don’t need to live in the tropics to grow this showy shrub. Sure, the tropical hibiscus (Hibiscus rosa-sinensis) is relegated to U.S. Department of Agriculture plant hardiness zones 9 through 11 if grown outdoors, but the hardy hibiscus (Hibiscus aculeatus, Hibiscus coccineus, Hibiscus grandiflorus, Hibiscus laevis and Hibiscus moscheutos) tolerates winters in USDA zones 5a through 10. Both types can be grown in containers, indoors or out.
Hardy or Tropical
Hardy hibiscus plants differ from the tropicals not only in the amount of cold they can tolerate but in some of their care requirements as well. Although they thrive with consistently moist soil, and will tolerate a bit of dry soil, overwatering them in the winter when the soil is cold may cause root rot. Tropical hibiscus requires consistently moist soil as well. Imagine a sponge that you’ve wrung all the water from to get an idea of the moisture content of the soil required by both types of hibiscus. The tropical hibiscus doesn’t die back in the winter, so provide just enough water to keep the soil from drying out during this time.
Watering a Potted Hibiscus
Soil in planting pots tends to dry out quicker than the soil in the flower bed, so you’ll need to water both hibiscus types more often if they're planted in pots. Always plant them in pots with drainage holes in the bottom. To determine when to water the tropical hibiscus, insert your index finger into the soil up to your first knuckle. If it comes out dry, it’s time to water. With a potted hardy hibiscus, measure soil moisture to the second knuckle. To ensure that the entire root ball is moist, water slowly and stop watering when water runs from the bottom of the container. Wait for the water to drain completely and repeat the process. During particularly hot weather, you may need to water an outdoor potted hibiscus twice a day.
In their native ranges, tropical hibiscus plants receive lots of moisture from humidity and rain. In dryer climates, irrigation needs to replace natural sources of moisture; the hotter and dryer the weather, the more often you’ll need to water the tropical hibiscus grown in the ground. The experts at Hidden Valley Hibiscus suggest watering the plant once a day when the air temperature is between 70 and 80 degrees Fahrenheit; increase the frequency to twice a day when temperatures range between 80 and 90 degrees. This same schedule works for the hardy hibiscus.
Amount of Water
The average root depth of the hibiscus is 6 inches, so you’ll need to soak the soil to that depth when you water them. The best way to ensure that you're providing enough water is by installing a drip system or using soaker hoses. Depending on the size of the hibiscus, you may need to use more than one soaker hose. Place the first soaker hose 6 inches away from the base of the shrub, completely encircling it. Place the others 6 inches apart until you reach 1 foot beyond the drip line. Dig a narrow hole, 6 inches deep, at the drip line. Time how long it takes until the bottom of the hole is moist to determine how long to run the hoses.
- Visage/Stockbyte/Getty Images