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Rosemary and Gardenias: Everything You Always Wanted to Know

by Taylor Miller

Tags: Question and Answer, Tips, My Garden, Taylor Miller, The Garden Gnome,


Q:  Taylor, my question is multi-layered. I live in the Western NC mountains (Waynesville) at about 3500 feet. Last summer, I put out two upright rosemary plants in areas with Eastern exposure, also a winter-hardy gardenia and a trailing gardenia, none of which survived our winter this year. I learned a very expensive lesson. Therefore, they're going to need to be pot plants. My question: What dimensions/depth should the planters be for:

• Upright gardenia
• Trailing gardenia
• Upright rosemary
• Trailing rosemary
Also, finally, how long could they each stay in their respective planters at these dimensions?  How will I know they're unhappy?
Thank you so much for your help,

GardeniaA:  Admittedly, I’ve never grown gardenia plants before, but like I say to users who submit questions, either I will have an answer, or I’ll go out and find one for you. So, I spoke with a couple gardening experts, did some heavy reading, and arrived at a few learned suggestions for Lanie and the blogging community regarding gardenias, which are some of the most beautiful, most fragrant white flowers out there.

First, the quick answer: Pick a pot 2-4" wider and 4-6" deeper than the rootball of the plant you buy to start off the summer. You'll need to transplant them before the summer is through. Find out how to tell when they're ready, below.

1. Know your growing environment: 

Gardenias originated in an oriental environment with mild winters and warm summers – so in a region 6 growing zone, even when labeled “hardy,” if they aren’t in a protected area, they’ll freeze. So, at least with the gardenias in your area, you’re right to pot. (Note: Gardenias will thrive in warmer growing zones throughout the winter.)

While outside, your gardenia will want bright, filtered light (not direct sun), and it will want to stay at a temperature around 73 degrees Fahrenheit. When you move it indoors over the winter, however, it will need the brightest window.
2. How to pot: Gardenias are very finicky and like acidic, moist (but not TOO moist) environments, like azaelas, so it’s smart to mix your own potting soil rather than using a standard “garden variety” like Miracle Gro.

Fill the pot half way with organic top soil and then add a handful-or-so of coffee grounds to lower the PH level (make it more acidic). Mix thoroughly. Now add a third more top soil and find some dead leaves to mix in. Leaves will help the plant with moisture, but more importantly, this organic material will help the soil retain acid from the coffee. Finish with enough top soil so that the plant sits right below the mouth of the pot.

Gardenias will want an acidic PH level between 4.8 and 6.2. When mixing your own soil, especially when it’s this specific, it’s best to make only enough for what you need at the moment. Occasionally top soil will come with a PH reading, but if not, any garden center should be able to test the soil for you if you are really concerned with a correct balance. You will also want to refertilize your plants in mid-summer, near the end of June. This can be done with either more coffee grounds or an azaela fertilizer that's commercially available.

Most resources say that, outside of over-watering, an alkaline soil environment will kill your plant fastest, or prevent root formation, which inevitably stops the plant from coming back in the spring. Although they may have been fine during the growing season, it is possible that the plants had stored most of their resources in their leaves and could not grow back from their roots.

(About PH: A soil PH of 7 is neutral. Anything below is acidic and above is alkaline. Stones and building materials like limestone, gravel and concrete are alkaline and can affect the surrounding soil, so if you plant gardenias into the ground, it is best to plant them away from the foundation, walkways and driveways of your home to avoid difficult PH balancing.)  

3. Don’t over/under water: Water your plant every second day, because unlike most outdoor plants, gardenias are very susceptible to root rot, so you only want to water when they are nearly dry. On the second day, you’ll want to soak them well but make sure the plant is not sitting in water (drainage holes in pots are essential with gardenias), and saucers should be emptied.

The best way to ensure that your gardenia is watered (but not overwatered) is to mulch. Using a cedar mulch around the base of your plant will discourage pests (which are common with this flower) and will hold mositure in for a long period of time. This moisture is released more slowly into the soil, so the roots aren't sitting in a pool of water.

Some say that misting gardenias is important, which is in a way, true. Gardenias need humidity - but if they are over-misted and water begins accumulating, their leaves may also begin fostering black fungus, so take it easy with the misting, if you do it at all. Much like with indoor orchids, a better option when you bring the plant inside is to set it on a pebble tray filled with water. (Note: Do not sit roots in the water, instead set the pot above the pebble tray using a small clay saucer turned upside down).

When is the plant unhappy? You will notice that your plant needs to be upgraded to a bigger pot when the soil dries out very quickly because of the size of the roots eating up all the water. Gardenias like to be tight in their containers but not root-bound. And they should be transplanted when necessary, perhaps a few times throughout the growing season, to encourage the maximum amount of growth.

Several sources say that the best gardenia flowers for pots are the more vigorous growers, such as Belmont or Miami Supreme.

About your rosemary:Rosemary

Herb Companion garden columnist and herb expert, Jim Long, said that it is possible for you to raise rosemary outside your home in your growing zone in North Carolina, and may be preferable to potting it. He said he learned an important lesson about rosemary from one of his mentors, Madalene Hill, late president of International Herb Association: It’s not the heat of the summer or the cold of the winter, but how you treat your plant.

Clipped directly from Jim’s blog:

“[Madalene] went on to explain that rosemary plants have very small root systems and suggested I try this: Plant the rosemary plant in the garden in the spring, regardless of what size the plant is. Grow it all summer and after the first frost, dig the plant, repot it and bring it indoors. Keep the plant in an unheated room, with light, like a garage window or unheated back enclosed back porch. The following spring, unpot and plant the rosemary back in the garden, then leave it alone. And by golly it works! I followed her advice and have rosemaries in the garden that have been there almost 10 years, growing quite happily.”

After reading that, I think it’s still important to exercise caution with your rosemary plants. So, try an experiment; plant two rosemary plants directly into the ground and two in pots following the instructions above. You might find that, when the plants are sown directly into the ground, they will develop larger and more fully than those grown in pots. It is also very difficult to give rosemary the requisite amount of humidity it needs when planted indoors (and not allowed to go dormant).

Plant rosemary in full sun, or slightly filtered light, allowing the potting soil in containers to almost dry before watering; it’s also important that your potted plants have good drainage. Transplant at the same depth as they were growing in the nursery, with a neutral soil PH. Cactus soil with a bit of perlite is your easiest option

You can read more about growing rosemary in challenging conditions from Jim’s post and check out his blog.

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