Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
A friend emailed me asking for help with a gardenia houseplant that she had been gifted. It wasn’t doing well. She had researched the plants but couldn’t find any answers. Did I have any idea what might be wrong with her plant? This was a no-brainer. Gardenias need acidic soil and her plant was most likely growing in regular potting soil with a neutral pH. I told her to buy some Miracid to lower the pH of the soil. Miracid has been around for years and is the most popular product on the market for acid loving plants. It’s my go-to recommendation for lowering the pH of soil both indoors and outdoors.
What are Gardenias?
Gardenia (Gardenia spp.) is a genus of small flowering trees that are native to Africa, Madagascar, Asia and the Pacific Islands. They are related to coffee trees. They are popular because of their fragrant flowers. The different species of gardenia range in size from 3 to 50 feet tall. The flowers, usually white or cream color, also differ depending on the species. They can be single or double and as small as 2 inches across or as large as 4 inches across.
The most popular gardenia species is G. jasminoides. These are smaller trees that usually only grow to 6 feet. Because they are only hardy in zones 8 – 11 most gardeners grow them indoors as houseplants. When grown as houseplants, they usually only attain a height of 18 inches.
Their glossy dark green leaves are evergreen meaning they don’t die and fall from the trees in the fall. They stay green and healthy year-round. The flowers are white. They are among the larger gardenia flowers, being double and about 4 inches across. Bloom time is summer through early fall.
How to Grow Gardenias Outdoors
If you live in growing zones 8 – 11, you are in luck. You can grow gardenias outdoors. As previously mentioned, these trees need acidic soil with a pH between 5.0 and 6.5. You should have a soil test done on the soil where you plan to plant your trees. A soil test will determine not only the pH of your soil, but also the nutrient content of the soil. If done in a professional soil lab, your results will also have suggested amendments to add to your soil to enhance its fertility. Ideally you should have your soil test done 6 months before you plant your trees to give the amendments, including the acidifying one, a chance to work their way through your soil.
Gardenias love the sun, but need protection in warmer areas from too much sun. Try to plant your tree where it will get morning sun and partial shade in the afternoon.
These trees need 1 inch of water each week. If your area is going through a drought period, water your tree weekly to make sure that it is getting that critical 1 inch of water.
Gardenias should be fertilized twice a year with a slow-release fertilizer that is formulated especially for acid loving plants. Apply the first time in mid-spring and then again approximately 6 weeks later in mid-summer. No matter how tempting, do not fertilize your tree in the fall. When you fertilize, it encourages the tree to produce new growth. New growth in the fall will not have enough time to harden off before winter, so it will die.
How to Grow Gardenias Indoors
Those of us in colder climates have to grow our gardenias indoors as houseplants, only moving them outdoors temporarily during warm weather. They are notoriously difficult to grow indoors but with a little care, you can be successful.
There are potting soils that are specifically formulated for acid-loving plants like gardenias. Make sure you use one when potting or repotting your tree.
Light and humidity are the biggest stumbling blocks to successfully growing gardenias indoors. Our homes are not light enough for sun loving plants. If you have a sunroom or greenhouse, grow your tree there. That way they get sunlight on all sides instead of just one side as they would in front of an ordinary window.
Our homes are not just too dark, they are also very dry from a plant’s point of view. We have dehumidifiers on our HVAC units to prevent mold from growing. You will need to provide extra humidity for your tree. Purchase a humidifier and place it nearby. Misting alone will not provide enough humidity.
And don’t forget to water! The soil will need to be kept moist. Don’t allow it to dry out. Consistent watering is key.
Fertilizer is especially important for plants grown in pots because every time you water, the water leaches nutrients for the soil. You need to replace those nutrients. Either use a slow release fertilizer or fertilize your tree every two weeks with a soluble fertilizer. Use a fertilizer that is formulated specifically for acid-loving plants.
You can move your gardenia outdoors in the spring when the night time temperatures are consistently above 60⁰F. Move it back indoors in the fall when the night time temperatures fall to 60⁰F. Gardenias are very sensitive to cold temperatures so when it is indoors make sure that it is out of the way of any cold drafts.
Another spring chore: repotting your tree. They usually need to be repotted every two years.
How to Prune Gardenias
Whether grown indoors or outdoors, gardenias benefit from regular pruning. Prune your tree after it finishes blooming. This is because the buds for next year’s flowers form this year. If you prune your tree in the spring before it blooms, you risk cutting off buds so you will have few or no flowers.
Make sure you first prune away any dead or diseased branches. Then you can prune to shape your tree or manage its size.
© 2020 Caren White
Abby Slutsky from LAFAYETTE HL on July 22, 2020:
I appreciate the encouragement.
Caren White (author) on July 22, 2020:
Thank you for your kind words. Practice makes perfect! I'm sure that your thumb will be green in no time.
Abby Slutsky from LAFAYETTE HL on July 21, 2020:
You are very talented and passionate about your gardening. How wonderful! I used to have a complete brown thumb. I would now rate it a rusty yellow. (I grow magnificient weeds, mint, calla lillies, and daisies, and this year I have a herb garden on my window sill.) Thank you for sharing your knowledge with us.
Caren White (author) on June 24, 2020:
You're welcome! Thank you for taking the time to read this. Glad you found it helpful.
Theblogchick from United States on June 23, 2020:
I think gardenias flowery plants are very awesome. I didnt know you can also grow them indoors. Thanks for sharing this interesting and informative hub.
Caren White (author) on June 21, 2020:
Agreed. It's difficult to grow them indoors but the scent is the payoff.
Mary Norton from Ontario, Canada on June 20, 2020:
I love the smell of gardenias in the garden, and I always envy family and friends with gardenias in their Florida garden. It is harder to grow them outside in Canada, but I did try indoors. It is not as healthy and robust as I would want it to be.
Caren White (author) on June 19, 2020:
Glad to be helpful. Thanks for stopping by.
Marisa Wright from Melbourne, Australia on June 19, 2020:
Living in Australia, it never occurred to me that gardenias could grow indoors! I adore gardenias but I have a very exposed, windy balcony, so I'd resigned myself to not having one. I may rethink!