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Hibiscus

Overwintering Hibiscus

By: Sandy Feather ©2008
Penn State Extension


Q. I purchased a hibiscus plant this past spring that is four feet tall and growing in a 10-inch plastic pot. I brought it into the house in mid-October, where it seems to be doing well, even continuing to bloom. Is it all right to keep my hibiscus indoors through the winter? How often should I water it? Should I move the hibiscus into a larger pot, and is another plastic pot suitable? Should I fertilize it, and if so, what kind of fertilizer should I use and how often should it be applied?
  A. There are hibiscus species that are perfectly winter hardy in our climate, including Rose-of-Sharon (Hibiscus syriacus) and large-flowered hardy hibiscus (Hibiscus moscheutos) cultivars such as Disco Belle Mix or ‘Lord Baltimore.’ Even though these species are winter hardy when planted in the ground, they would probably not survive the winter outdoors in such a small pot.
  

It would be preferable to overwinter hardy species of hibiscus in an unheated, attached garage where they would experience winter dormancy, but still be protected from bitterly cold temperatures.

Winter Hardiness

Tropical or Chinese hibiscus (Hibiscus rosa-sinensis) is not winter hardy in our climate and must be brought indoors for the winter. It is difficult to say what kind of hibiscus you have from your description, although its performance indoors leads me to believe that yours is a tropical variety.
  

White Hibiscus flower
Hibiscus syriacus 'Diana'
1991 Gold Medal plant award

'Diana' is winter hardy in USDA Zones 5 - 8

(Click to enlarge)

Chinese hibiscus is an attractive houseplant if you can give it the very bright light it requires to grow and bloom well indoors. A west or south-facing window that gets five or six hours of direct sun daily is best. It sounds as though yours is getting adequate sun since it is still blooming.

Unheated Garage

Even without ideal conditions, you can keep a Chinese hibiscus alive through the winter. A cool (50 - 60°F) place such as an unheated, attached garage where it can get some light works well. It will lose most of its leaves and all of its flower buds when you move it into such a situation. However, the plant should survive the winter and leaf out in spring when temperatures warm and you can place it outdoors again. Be sure the overwintering location you choose will not fall below 50 degrees. Temperatures lower than that can severely damage tropical plants.

Winter Conditions

Adequate, but not excessive watering is important for winter survival. Chinese hibiscus prefers evenly moist soil, but it should drain well to avoid a perpetually waterlogged condition. Conversely, you do not want the soil to dry out to the point where your hibiscus wilts. The pot it is growing in must have drainage holes. How often you water depends on a number of factors:
  
• The amount of sun the plant receives indoors. Plants that receive enough sun to continue to grow and bloom indoors use more moisture than those overwintered in darker locations where they are dormant.
  
• The size of the container it is planted in. Larger pots hold more moisture than small pots.
  
• The potting mix. Very light, soilless mixes dry faster than those that contain soil.
  
• Whether the container is plastic or clay. Plastic pots tend to hold moisture longer, while porous clay pots lose moisture from the sides as well as the soil surface. Plastic pots are fine as long as you do not overwater.
  
• The temperature. Plants grown in warmer (65 – 75 degrees) locations use more water than those grown in cool locations.
  
• The relative humidity in your home.
  
You certainly will not have to water as often as you did when it was actively growing and blooming outdoors. Feel the soil two or three inches deep, and water when it feels dry. Carry it to a sink or bathtub and water until water runs from the drainage holes in the bottom of the pot, and return it to its location when it stops draining.

Fertilizer

Since your plant is blooming and doing well indoors, you can fertilize it once a month with a balanced, water-soluble fertilizer such as Peter’s 20-20-20 or Miracle-Gro. Always follow label directions. When it comes to fertilizing, more is not necessarily better. If your plant is spending the winter in a darker, cooler location where it is dormant, do not bother to fertilize until you move it outdoors in the spring.

Transplanting

Wait to repot it until you are ready to move it outdoors for the summer. It will recover from transplant shock faster when it resumes more active growth in spring. Although that 10-inch pot sounds small for a 4-foot tall plant, it also depends on how deep it is.  Remove the pot and check the rootball. If the roots are growing in a tight circle, your hibiscus is root-bound and should be moved into a larger container.  Avoid the temptation to move it into a huge pot, though. One or two sizes bigger is sufficient. If you move a plant from a small pot into a very large one, the soil volume may hold too much water for too long a time and cause root rot. Be sure to untangle any circling roots before placing it into the new container, and prune roots back rather than coiling them to fit.

Moving it Outdoors

You can move your Chinese hibiscus outdoors when all danger of frost has passed in the spring, right around Memorial Day. Do not put it out in the full blazing sun right away, though. Gradually acclimate it to brighter sun over a seven to ten day period. Move it to a sheltered location such as a porch, or the filtered shade under a tree. Expose it to direct sun a little more every day until it is out in full sun for the whole day.


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