So how cold-hardy is Rosemary?

My rosemary looks fine after weeks of 20-degree weather

One of the many mysteries of gardening is the contradictory advice we read, especially but not solely on the Internet, about plants.  It can even contradict our own experiences growing plants in our very own gardens, so what’s a gardener to do?  I always go with my own experience – and keep an eye out for why mine was different.

Take this rosemary, for example.  According to everything I’ve read, it can’t survive freezing temperatures – yet here we are in late January after an unusually wintery December, and this specimen on my deck is just fine, thanks.  And don’t tell me that’s because it’s up against the house and therefore in a “sheltered location” because I only moved it here for the photo.  Its real location is out at the edge of the deck, fully exposed to the wind.

But I’ll back up and tell you what some online sources I usually find trustworthy are saying about rosemary.  Garden writer and horticulturist Marie Iannotti tells us, “The three fundamentals for successfully growing rosemary are: Sun, Good Drainage and Good Air Circulation. Provide a sandy, well draining soil and 6-8 hours of full sunlight. ”  Then about winter-hardiness, “If you live in a frost free area, you can grow rosemary in the ground year round.  Where the winter temperatures dip below 30 degrees F., rosemary plants will have to spend the winter indoors.”  See, as though it can’t take frost!  And from Fine Gardening Magazine we learn that: “In the fall, when the temperature dips to 30ºF, it’s time to bring rosemary indoors.”

Source after source repeats this warning that rosemary can’t handle temperatures below 30.   So I posed my burning questions to Kerry Kelley, Homestead’s manager of annuals, including herbs, and she replied:

There are a couple of varieties that we know make it in our zone 7.  ‘Arp’ rosemary is considered the hardiest.  It’s an open, upright plant that should do fine here with proper siting.  Also ‘Hardy Hill’, but that’s not as frequently commercially available.  Some people with zone 8 microclimates (Capitol Hill, inner city Baltimore, close to the bay, or just a warmer, protected spot) may be able to grow other varieties–some success had been had with ‘Tuscan Blue’.

Also consider that the bottom temperature for zone 7 is 0 degrees and for zone 8 I think it’s 10 degrees.  If we have a relatively mild winter, with only sporadic temps below 10, other varieties may last.  But when the REAL Maryland winter returns (if it ever does), the plant will be toast.  In other words, plants may do fine for a few years, and then we have one hard winter and the fun’s all over!  And that’s true of any zone 8 plants, not just rosemary.  A warm spot near the house protected from north winds is the best bet.  Plants really should be in the ground and not in a container, since roots are not as hardy as top-growth.

I love one of the tips one of my customers gave me about using rosemary: she sprinkles the flowers on her family’s breakfast eggs–beautiful and delicious.

Rosemary flowers sprinkled on eggs – what a wonderful image!

But I’ll end with what everyone seems to agree on: that as a Mediterranean plant, rosemary likes it sunny and dry – which means great drainage, something that pots usually do a good job of providing.  And rosemary can be pruned to almost any shape, so it’s popular among enthusiasts of topiary.

Posted by Susan Harris.

9 Responses to So how cold-hardy is Rosemary?

  1. Pam J. says:

    I’ve lived in the same house in Silver Spring, MD, for 24 years. I started planting rosemary within the first year or two, and have added many kinds of rosemary over the years. They all live through our below 30 degree weather. All of them. They bloom year round, more in the spring, summer, and fall but also in the winter—not a lot of blooms but some, and I have pictures to prove it. In the 20-inch snow storm we had in December most of my huge rosemary plants were buried. I knocked off some of the snow, but not all. Gradually, as the snow has melted, all the rosemary has sprung back. I have a few broken limbs but just a few. And everything is living. It’s an amazing and reliable plant for my climate.

    So you make an excellent point Susan, about trusting our own experience in the gardening realm.

  2. Jeff says:

    One other thing to consider is that having plants near the house (as in the picture) does provide some shelter and perhaps ambient warmth which might mitigate some of the cold. Obviously it isn’t going to raise the temperature much, but it does provide help from wind-chill, etc.

    Plants are individuals and react differently so generalizations are helpful, but plants do react somewhat differently.

  3. Jeff – is right, pulling a pot next to the house ups the temp and protection substantially. That being said, I’ve had my hardy rosemary overwinter in pots the last few years. We’ll see if it makes it this year again.

  4. Zee says:

    Enjoy reading this blog.

    I bought a few Rosemary plants two years back from Home Depot, and planted one of them outside, understanding they grow better outside, but was not sure if they could survive the winter season here.

    We were really delighted that it survived the winte of 2008-2009. That prompted me to give away one pot, and planted another Rosemary plant outside last year. But I dont’ think they survived the bitter 2009-2010 winter season.

    Our family cherished these wonderful plants. And I determine to get new ones.

    I live in Fairfax County, and have made some trips to Home Depot and a local nursery, but have not found any.
    Have you recently see them for sale in DC area ?

    thanks.

    • Felecia says:

      Hi Zee,
      I just bought a beautiful large Rosemary Plant at the Fort Belvoir Commissary for $5.00. Hopefully you know someone who could pick one up for you.
      Good Luck

  5. Susann says:

    We live in Eagle, Idaho, in a low micro-climate below the foothills & mtns, just NW of Boise (So. Idaho). Our mid-late December 2009 was horribly cold (dipping to -15 at night and barely above +5 during the day). We were in So. Arizona at the time and weren’t aware it had reached those low temps while we were gone…..until our hardy Bendenen Blue Rosemary was not showing any signs of new life this spring. We’ve had this “shrub”, outside and in-ground, for 10 yrs, started from a cutting from the parent plant at our previous home. We never once mulched it or covered it in winter and the base grew to about 10″ circumf in 10 yrs. We pruned back the winter kill every spring – but a good grooming brought it back to beautiful life every year – normally. Our shrub was on the south side of our home, about 4 ft from the house, but exposed to winter cold winds, and we always felt it was a perfect place for it because we get so much sun here all year around, even when it’s zero. But the 3 weeks of cold temps ranging from -15 to +10 was too much for our Rosemary and now we are looking for a replacement. To our amazement, the local nurseries are sold out of the gal size plants; it seems we weren’t the only one’s who lost our Rosemary to the cold. The variety we had was amazing – after spring pruning to about 2 ft, it would ultimately grow again to 3.5 ft high by fall, and 4 ft wide, with beautiful sky blue flowers in late spring. I only wish I had the forsight in the previous spring to take a cutting for future spring.

  6. artsy ant says:

    Thanks for doing that research, very helpful. I am still debating if I should take it inside from tonight on but is seems as though shielded spot facing south should be just fine for my dear Rosemary (raised from seed, so proud of it).

  7. bill crandall says:

    My rosemary has taken no visible damage with temperatures down to 8F, here in the Mojave Desert. The cold snaps are not prolonged, and the plants have a white wall to their north or east, and are on high ground. They are also thickly mulched. In mild winters, they bloom through January, and I plan to propagate them through much of the yard as a ground cover, partly to keep the bees coming here when nothing else is blooming.

  8. Paul d'Aoust says:

    Interesting — it seems like there’s so much variance in the tolerance of rosemary plants. I bought some sort of rosemary plant from our local garden centre a few years ago — I think it was ‘Arp’, but I’m not sure if it even had a label on it. Anyhow, it spent two bitter winters (as in, periods of -20°C or -4°F) in a pot out on my deck. I was sure it would’ve died (especially with its roots above ground), but it just kept on trucking.

    So this year I decided to plant it in the ground. This winter was milder, but as spring approached it abruptly died. Why?!

    I have a couple somewhat educated guesses…

    First, I know rosemary hates getting soggy in the cold, especially around its roots. Perhaps when it was in the pot I forgot to water it, and that’s what saved it?

    Second, it was a weird winter; it would dip down to -15°C (5°F) and then go back up to 5°C (40°F), and then go back down again. Perhaps the successive thawings did it in.

    Third, it was in a windier spot than before.

    Fourth, I know a frosty night can be more damaging than a dry night at the same temperature. Maybe in late winter there were a couple nasty frosts?

    Interesting. Anyway, I have ideas for next year. And here’s an interesting article from someone overwintering in conditions much worse than mine and yours: http://forums.gardenweb.com/forums/load/herbs/msg01092721714.html

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