How Cold Hardy Are Gardenias, Really?
How cold hardy are gardenias, really? The emerging answer is currently shivering its ass off in my garden.
By John G. Stamos
Table of Contents
How Cold Hardy Are Gardenias, Really? An Introduction
Welcome, readers and subscribers. Please accept my apologies for my recent hiatus. It’s been a rough stretch here on the homefront, but it’s great to be back. I thought some gardening chatter might be just the thing for a good, solid reacclimation. So let’s get to it.
For most gardening type folk here in the United States, the word “gardenia” typically evokes thoughts of antebellum verandas on sweltering June days, and of white, insanely fragrant blooms nodding in subtropical breezes. Not many would ever think to use it in the same sentence as “freezing temperatures.” For most gardeners, “gardenia” is a warm weather word, and gardenias are warm weather plants. And there’s a pretty good reason for that.
Of the 128 different species of the genus Gardenia, the most well-known to gardeners is Gardenia jasminoides, also known as the Common Gardenia, or Cape Jasmine. It’s the species that’s predominantly grown for ornamental use in cultivated gardens in the United States and throughout the world, and it’s the one we’ll be talking about here today. And it is mostly a tropical/subtropical/temperate zone species. There are dozens of jasminoides cultivars, varieties, and hybrids, and most are hardy only in USDA hardiness zones 8-11, where the absolute coldest temperatures don’t drop below 10° Fahrenheit. These are, without a doubt, plants suited for the warmer parts of the globe.
There are, however, some exceptions to this fact. Believe it or not, some gardenias are actually fairly cold hardy.
But not very many. In fact, out of all of the known jasminoides cultivars, varieties, and hybrids, only a handful can survive in USDA hardiness zone 7, where winter temperatures, at their lowest points, drop to between 10° and 0° Fahrenheit. Even fewer (maybe as few as four) can survive in zone 6, where winter temps can fall to between 0° and -10° Fahrenheit; and even then, almost all of these super cold hardy, zone 6 gardenias should be planted primarily in sheltered locations in order to make it through the coldest winter nights and days. In fact, my research (through internet searches, discussions with experts, and now, as you’ll soon read, from personal experience) shows me that there’s really only one jasminoides cultivar that is fully hardy – whether sheltered or out in the open (as long as it is properly mulched) – in USDA hardiness zone 6, and possibly – possibly – even down into 5B (-10° through -15° F). It’s the one currently growing in my zone 5B/6A garden here in Michiana Shores in the good old U.S. of A. It’s Gardenia jasminoides ‘Summer Snow,’ patent number PP22797 and varietal number Bab1183: the Summer Snow® Gardenia.
How Cold Hardy Are Summer Snow Gardenias, Really? The Basics; Some History; Notes from the Field
So, how cold hardy are Summer Snow Gardenias, really? Are Summer Snow Gardenias really cold hardy in hardiness zone 6? I’m going to answer these questions in two ways: 1) The short way, which involves some very basic plant info and history, and 2) The only-a-little-bit-longer way, which involves my field notes and a few pics. The whole thing’ll be painless. I promise. Here you go…
1) The Short Way
The basics.
Height – 4′-5′. Spread – 4′-5-. Light – part sun to full shade. Bloom color – pure white double blooms. Bloom time – late May through June (may vary by zone). Foliage – deep green, thick, waxy, and evergreen to semi-evergreen to deciduous (varies by zone). Hardiness – zones 6-10. Growth rate – medium. Pollinators – bees, moths, and to a lesser extent, butterflies. Soil – slightly acidic to acidic, moist but well-drained, with good amounts of organic material.
Some history.
Gardenia jasminoides, as a species, is native to southeast Asia, and has been in cultivation in China for over 1,000 years. Growers of this species of gardenia definitely have had a lot of time to develop a whole bunch of different cultivars, varieties, and hybrids; and they’ve had a lot of practice sharpening their cultivating skills. So it’s sort of surprising that a gardenia plant that could truly stand up to subzero temperatures wasn’t developed until only very recently. Gardenia jasminoides ‘Summer Snow,’ developed by Douglas I. Torn and grown by Buds & Blooms Nursery, Inc., was patented on June 19, 2012. Buds & Blooms Nursery is the owner of the patent.
I’m neither a botanist nor a horticulturalist, so I wouldn’t know or understand the methodology behind Torn’s brilliant development of this super tough cultivar. But the Summer Snow Gardenia has been finding its way into northern gardens throughout the United States for more than the past decade, and I haven’t heard of anyone bitching. So Torn’s horticultural genius, and Buds & Blooms Nursery’s growing expertise, have evidently resulted in the successful introduction of a plant, traditionally know for its hot weather charm, to some comparatively frigid gardens here in the Northern Hemisphere.
2) The Only-a-Little-Bit-Longer Way
Notes from the field.
My baby Summer Snow. I ordered my cold hardy Summer Snow from a reputable online nursery last spring. The plant arrived in mid July in a 2″ pot and was little more than a tiny twig with a few green leaves sprouting from it. But it was clearly healthy. I immediately transferred it to a 2-gallon pot filled with a slightly acidic potting soil. I placed it in a part sun location, kept its soil moist, and watched it grow over the next two months to almost a foot in height and spread. At this point I planted it in the ground. I had excavated a massive hole and had filled it with the same slightly acidic potting soil in which the gardenia had been growing. I modified this soil with my go-to Espoma Soil Acidifier, and for added measure, mixed in a little bit (about 1/4 of the recommended amount for an established plant) of Espoma Holly-tone organic evergreen food. Then I planted the gardenia, added a fairly substantial wood chip mulch layer (2″+) over the soil, and watered it all in. And watched it.
Autumn performance. For the most part, our fall here was a mild one. The little gardenia put out a few more leaves in October and remained healthy and green. I kept it watered and decided that I’d let the plant face the coming winter with only the existing wood chip mulch layer for protection. It remained healthy and robust (at least as robust as a 1st year baby gardenia bush can be) as the temperatures began to drop into December.
The cold hardy Summer Snow Gardenia in winter. December 2022 here in Michiana Shores started out in typical December fashion: cold, but not brutally so. And precipitation was limited through much of the month. Throughout this time, and during these conditions (average temperatures between approximately 32° and 38° Fahrenheit), the baby gardenia remained as green and healthy-looking as ever.
Then the bottom dropped out.
In the several days leading up to Christmas, daytime temperatures plummeted into the teens, and nighttime temperatures averaged around 0° Fahrenheit. The three coldest nights were -7°, -5°, and -3°. And two days before Christmas, approximately 12″ of snow fell in Michiana Shores. The little gardenia was subjected to several nights of subzero temperatures, and an obliterating blanket of super cold snow.
Christmas came and went, and, after a few more days of arctic-level temperatures, the weather broke. Daytime temperatures climbed into the 40s and 50s. The crazy unseasonable warmth melted the snow that had blanketed our land and my garden, and the little Summer Snow Gardenia bush, after being completely covered by snow for several days, was once more greeted by the light of day.
But now it looked a lot different.
The green glossy leaves had turned brown. The plant did not look at all dead, but it didn’t look like an evergreen either. I wasn’t worried. My research told me that this particular jasminoides cultivar would behave as a deciduous bush in the coldest limits of its hardiness range. A friend of mine, a lifelong gardener in hardiness zone 6A, owns two of these bushes which survive each winter, but drop their leaves during the most frigid cold snaps. Although I couldn’t be sure, I’d estimate (based on my own little bush’s performance, and my discussions with other gardeners in warmer zones) that the Summer Snow Gardenia bush probably remains evergreen in zone 8 (or possibly even zone 7) and above. In any case, although winter was far from over, I was confident that my Summer Snow would persevere.
Assessment in the cold light of day. With my current view of this bush completely unimpeded, I can see that its main stems, branches, and nodes remain healthy. They display the telltale green color of a living, healthy – if dormant – plant. If I had to bet, my money would be on this bush all the way across the board. Once again, I’m pretty damned sure this little guy is going to cruise through the rest of this winter with no problem.
So how cold hardy are Summer Snow Gardenias? Considering that mine was a tiny twig in a 2″ pot in July of 2022, and is currently alive and healthy after subzero temperatures and a blisteringly cold blanket of snow, I think it’s definitely safe to say that these gardenias are really cold hardy. Really, really cold hardy.
Note: The plot of this plant’s story has got some serious twists and turns to it. Click here to read its surprising conclusion.
How Cold Hardy Are Gardenias, Really? Give Them the Right Care and You'll Be Amazed
Suggestions for Making Sure Your Cold Hardy Gardenias Stay That Way, and That They Stay Warm Hardy, Too
Keep the soil slightly acidic to acidic. All gardenias love soil that’s at least slightly acidic. The cold hardy cultivars are no exception. The pH level of the soil in which my gardenia is bedded is somewhere between 6.0 and 6.5, and the bush has performed beautifully. Below, you’ll find some handy-dandy products for acidifying your soil, and analyzing it to make sure that it’s been acidified to the proper levels.
Mulch and water. A generous layer of wood chip mulch covering the ground where your gardenia grows serves as both an insulating and moisture retaining element. The mulch will keep the plant’s roots warm in winter, and cool in the summer. And it will help keep the ground beneath it from drying out too quickly once you give your gardenia the water it needs. Although they’re fairly drought-tolerant once they’re established, gardenias always appreciate moist, well-drained soil. This is especially the case with newly planted bushes. Feel free to give your gardenia an occasional drink throughout the winter, especially on warmer days.
Feed. Although my Summer Snow Gardenia behaves like a deciduous bush during the cold winters of my zone 5B/6A garden, it’s still classified as an evergreen. And it’s definitely an acid-loving evergreen. A high quality organic fertilizer formulated for evergreens is in order here. Maybe even two. You’ll see my recs below. It’s important to remember that a gardenia is going to need that slightly acidic/acidic soil I mentioned earlier. This acidity allows the plant to effectively assimilate nutrients from any fertilizers you may administer.
Know your zone. If you’ll notice, at the very beginning of this article, I wrote that most Gardenia jasminoides cultivars, varieties, and hybrids are hardy in zones 8-11. Even though Summer Snow has much better cold hardiness than these warm/hot weather guys, its ability to withstand excessive heat is not quite on par with theirs: its top end is zone 10.
Recommended reading. I suggest giving my article from last year about fixing chlorotic (yellowing) rhododendrons a read. It outlines an excellent methodology for keeping rhodies, azaleas, and pieris healthy and green. This methodology will also work perfectly for gardenias. I’m going to implement it for my Summer Snow starting this spring. I also recommend reading my article explaining how to lower soil pH for acid-loving plants. The plan I outline there is relevant and helpful as it pertains to gardenia planting and care. Finally, I recommend clicking here to read Buds & Blooms Nursery’s info page on the Summer Snow Gardenia. It’s their baby. They know the most about it.
Product recommendations. The following are products which I use and wholeheartedly recommend. Their use will help ensure your own gardenia’s health and wellbeing for years to come.
I bought this Luster Leaf Rapitest 4-way soil analysis meter in February of 2022 and have used it successfully for almost a year to test for soil fertility and pH levels. It also measures sunlight and soil moisture levels. It’s fast, easy to use, convenient, and accurate. By using this device, I’ve been able to determine the necessity of appropriate fertilizer applications and pH amending to the soil of a large number of the plants in my garden. Order it here, directly from Amazon, by clicking the #advertisement link. Note that this unit doesn’t test for iron levels in soil. Also note that I really love this little meter!
Espoma Organic Soil Acidifier is the perfect product for lowering the pH and increasing the acidity of your garden’s soil. It’s a fabulous organic product which I’ve used to lower soil pH for plants like my blue hydrangeas and my rhododendrons, azalea, and pieris. It’s very effective and allows acid-loving plants like these to properly access and utilize nutrients from fertilizing products. Order it here, from Amazon, by clicking the #advertisement link.
Espoma Organic Holly-tone is the almost perfect fertilizer for acid-loving plants like gardenias, rhodies, azaleas, and pieris. It’s an organic formulation with an N-P-K of 4-3-4, a multitude of beneficial microbes, and a respectable amount of sulfur (5%) on tap for performing its own bit of soil acidifying. Like I said, it’s almost perfect. And when it’s used in conjunction with the fertilizing product listed below, it is perfect. Conveniently order it here, from Amazon, by clicking the #advertisement link.
Ohrstrom’s Maxicrop Liquid Seaweed Plus Iron is a remarkable source of iron for acid loving plants. When used in conjunction with Espoma Soil Acidifier and Espoma Holly-tone, it literally works miracles. It’s got an N-P-K of 0-0-1 and it contains 2% iron. It’s sourced from Ascophyllum nodosum seaweed harvested from the waters along Norway’s coastline. The beneficial effects of this product are noticeable almost immediately after its application. Click the #advertisement link to learn more and to order it here, from Amazon.
So, how cold hardy are gardenias really? I’ll tell you this: my ‘Summer Snow’ bushes, when given the proper soil conditions and feeding, are fully equipped to handle the cold of my hardiness zone. Good health shines in their foliage, pictured below.
Well, my dear readers and subscribers, it’s great to be back. I’m glad you stuck around for this one. If you’ve been thinking about a cold hardy gardenia for your own garden, I hope the material here was interesting and informative. And even if one of these tough little beauties isn’t in the cards for you, I’m hoping that you didn’t mind too much grinding it out with me here ’til the end. As always, I thank you for your interest and your readership.
Cheers, and Happy Gardening!
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Once upon a time I brought one home, it struggled and then said
” adieu” to this mortal coil ( and inept gardener person I’m stuck with ). Your lovely & comprehensive piece is resurrecting my interest in starting again next summer with a gardenia. My original interest stemmed from it’s fragrance but now I will be seeing the whole plant, not just a fraction of its value.
(✷‿✷) Hello John, it’s Violet from the tweeter.
Well hello, Rachel – I’m so glad that you’ve enjoyed this article, and I’m so happy to see you here! Thank you so much for reading the article, and, of course, thank you for your lovely comments. As I mentioned in the article, I’ve seen two mature examples of this particular cultivar growing in a comparitively cold zone (5B), both in full flower, and later the same summer, in full glossy green glory. I do hope you’ll take another crack at them. I’m glad to know that you’d be allowing the beauty of this plant to entertain your other senses. They really are gorgeous bushes. Mine is still a baby, but I’m expecting great things. Once again, Rachel, I thank you very kindly.
I’ve got succulents & gardenias on the ‘new’ list . I’ve also got to look into tree peonies again. Moved one and must have killed it, and the other one is not really where it should be. This garden is nothing if not a long learning curve .
Ha, what isn’t ? ｡◕‿◕｡
Wishing you the deep & abiding pleasure of success with your little baby plant.
Thank you for your kind wishes, Rachel. I am expecting big things from this little gardenia. I absolutely agree with your “learning curve” assessment – about gardening, and, as you’ve observed, everything else. Regarding peonies: they generally don’t take kindly to being moved. I was fortunate last year when I transplanted two Felix Crousse peonies from partial shade to full sun. I believe the sustained sunlight eased their transitions. In any event, I would love to hear how your gardenia/succulent adventures turn out. Pleas let me know. Thanks once again, Rachel
Can’t wait for summer to see how your little plant thrives and shares the intoxicating fragrance with the World!
Thank you! I’m with you on that one! It should be a real beauty!
Great article. Now I need to find a gardenia for Washington state 🙂
Thank you, Annie. Glad you enjoyed it! A good portion of Washington state (much of the eastern half) falls into hardiness zone 6A. You can enter your zip code into any internet zone-finding site to check if you’re in 6A. If you are, you’re good to go with the Summer Snow cultivar. It’ll be just fine. And it will grow big, and it’ll be covered with white, insanely fragrant blooms in the spring. Please keep me posted. Best of luck, Annie. And thanks again!
Washington state is a uniquely challenging environment to try to grow gardenias. The summers are not very long and the growing season is short, but gardenias only really put on much growth when the temperature is above 69 or 70 degrees F. But at the same time, Washington state still has hot dry summers, which gardenia plants do not tolerate. The secret seems to be that gardenias need at least some partial shade in the summer, preferably sun during the earlier part of the day, and appreciate a more enclosed location protected from winds that can help hold in the humidity. But the gardenia still needs a decent amount of sun exposure, especially during late Spring. So it can only grow within a very limited range of conditions in this climate. Absolutely needs consistent summer watering, especially during the rare heat waves, and during the first 2 or 3 years to get established.
You’re right on all counts, Parker. As you’re not mentioning your specific location’s hardiness zone, I can only make the assumption that you’re in a warmer zone than I am (based on your earlier message in the “Contact” form in which you referenced growing a less cold-tolerant gardenia variety). But whether you’re growing them in a warmer zone than my own 5B/6A zone, or in the same zone, the facts that you astutely point out remain true. Gardenias, particularly during the period in which they’re becoming established after bedding, require ample watering. And they definitely don’t like to bake in the sun. I’ve found that a partial sun to partial shade location has worked best for mine. Also, the window of optimal growing conditions you cite is consistent with what I’ve observed in my garden. Another factor that I found to be important with my gardenias was maintaining soil acidity. At any time soil pH approached alkaline levels (7 or above on the pH scale), the beginnings of chlorosis became very evident. Although I did have luck growing two young ‘Summer Snow’ specimens in my hardiness zone (5B/6A) by heavily mulching them in prior to winter’s onset, and maintaining proper sunlight, moisture, and pH levels all year, they eventually succumbed to a number of assaults by woodland voles. For some reason, my gardenias became a favorite vole target, and even the most effective repellents didn’t seem to help (which was surprising, as I’ve experienced excellent results employing a highly effective combination of an excellent organic systemic repellent and a potent organic soil treatment repellent in the case of all of my garden’s other plants and bushes). In any case, your observations and conclusions are spot-on, and I certainly appreciate your taking the time to relate your experiences here with respect to your own gardenia bushes. And of course, I thank you for reading the article. Please feel free to reach out any time with new observations about your gardenias, or any of the other plants you might happen to be growing. Thanks once again, Parker.
What a great informative piece John,look forward to seeing pictures in future,hope you and family are well,thinking of you all
Thank you very kindly, Tina. I really appreciate it. And thank you for reading the article. I’m so glad you liked it. I was very happy to be able to add a gardenia to my garden. I believe this particular cultivar will fit the bill perfectly. And of course, all the best to you and yours, Tina. Thanks once again!
The beautiful gardenia flowers with their intoxicating fragrance … always thought they only did well in sunshine, not cold winter.., hopefully your gardenias will do fine (what a thing to say … for sure they are going to do well; you are the expert)🙏
Always such interesting and informative articles🙂🌹❤️
Thank you so much, Roxxy. I truly appreciate that. I was just like you for the longest time. Until not too long ago, I thought gardenias were only tropical/subtropical/temperate zone plants. I’ve got a number of friends in the southern states who grow them. But I know another gardener who started growing the Summer Snow cultivar 5 or 6 years ago in zone 5B, and they’ve done beautifully. So, it was Summer Snow for me! Thanks once again, Roxxy for your interest and your kindness. I dearly appreciate it.
It is going to be very interesting to see how your gardenia does. I hope it makes it, thrives and has that fantastic fragrance that I love!
Thank you, Kevin. I definitely believe that this little guy is going to make it through the winter just fine. And I totally agree with you. I’m absolutely crazy about that incredible fragrance!
I had no idea a gardenia plant could live in cold environment. Very informative
I’ve always loved gardenias. I’ve got a number of friends in the hotter parts of the US who grow them, and I’ve always been a fan. I was really excited to discover this extremely hardy version. Thanks for giving it a read, Rick. Truly appreciated!
Thank you John for this informative article! Always a fun reading!
Many thanks! I’m glad you enjoyed it. Thanks for having a read of it – much appreciated!