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Protecting Rosemary

January 26, 2013

Rosemary plant after two years of growth (photo credit: Jean Potuchek)Rosemary (Rosmarinus officinalis) is a must-have garden plant for me. I use this herb frequently in cooking, and I love the look and scent of it growing by the back door. In my Maine garden (USDA winter hardiness zone 5a, with typical winter low temperatures around –20 F), this plant must be treated as an annual, as it can’t survive our cold winters. (Some recommend growing it in a pot and bringing it inside in winter, but my occasional attempts at doing this have never been successful.) In my zone 6b Gettysburg, Pennsylvania garden, however, this plant could be thought of as a tender perennial. Local gardening lore is that it will survive down to about 20F and can be wintered over if given protection on colder nights.

Over the years, I have often tried to protect my rosemary plants from those cold winter temperatures – but never successfully. One year, for example, I kept a box by the patio door and would put it over the plant on cold nights. Inevitably, however, I missed one night and the plant perished. In this way, I have always ended up starting over with a new rosemary seedling each spring.

Last year, however, we had such an exceptionally mild winter that the temperature apparently never got down below 20F, and my rosemary plant survived. I was amazed by how large it had grown by the end of its second summer in the garden; suddenly those mythical rosemary hedges of milder climates seemed more real. And so, when a blast of arctic air descended over much of the eastern United States this week, bringing the coldest temperatures in over two years to my Gettysburg garden, I was determined to try to save my rosemary plant.

Recently, Noelle of the blog AZPlantlady posted advice for desert gardeners about how to protect their plants from freezing desert nights, and I decided to try to adapt Noelle’s advice to protecting my rosemary. So, when I got home from work on the night that the arctic air was predicted to arrive, I started looking around for something to cover the plant with. I would have been tempted to use a large dry cleaning bag, but Noelle warned against plastic, which she advises transfers cold to the plant rather than protecting it from the cold. I thought about using an old towel, but realized it wouldn’t be large enough. What I really needed was an old frayed bed sheet – but I didn’t have one and wasn’t willing to sacrifice good bed linens to the cause. Finally, I came upon an old nightgown, recently retired and waiting to be cut up into rags. It seemed as though this might work. I took the long sleeves of the nightgown and tied them around the neck opening to close it off; and then I took it outside and, by the dim glow of the patio light, draped it over the plant, trying to tuck all the branches under the protective covering.

rosemary coveredI didn’t succeed in following all of Noelle’s advice. In the light of day, it became clear that I had not covered the plant completely and eliminated all gaps where heat might escape. I have also not been able to remove the covering during the day to expose the plant to sunlight and warm air as Noelle recommends, because our daytime highs have only been in the teens. Tonight will bring our fifth night in a row of frigid temperatures, but a warming trend is expected beginning tomorrow, which will allow me to remove my rosemary’s nightclothes. Will my efforts bring my plant successfully through the winter cold? I probably won’t know the answer to that question until spring. But there was nothing to lose by trying.

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40 Comments leave one →
  1. January 26, 2013 8:57 pm

    I’m pulling for you and your Rosemary!

    • January 29, 2013 10:10 pm

      Thanks, Chad. I’ll really be disappointed if I lose it.

  2. January 26, 2013 9:11 pm

    Jean, I almost jumped from my chair when I read this! I have the same issue with rosemary and just this morning, I checked my plant, as I forgot to cover it through our several days of single digit temps this week. Mine is located between a basement door and a concrete stoop right up against the concrete basement wall -southern exposure and it looks like just the very tips got damaged. The rest looks fine. I can’t believe it. I would be willing to bet yours will come out just fine with the added nightgown you dressed it in- I’m sending good thoughts your way. Thanks-Sandi

    • January 29, 2013 10:13 pm

      Sandi, It sounds as though yours is in a more protected location than mine. Reading the comments below also make me wonder if my previous rosemary losses here have had more to do with lack of moisture than with low temperatures. Maybe I should be sure to give it a good long drink just before the first frost (especially since we don’t get reliable snow cover here).

  3. January 26, 2013 9:19 pm

    When you retire and move to Maine, you will need to learn to overwinter it indoors. My father is always successful because he does not heat his entire house, keeping parts of it at 50. There the rosemary does well in a sunny window. I have kept mine alive for several years now by putting it in a room that is heated to 55, but I do not have good sun exposure. By spring it looks pretty tough, but by carrying it outdoors any warmish spring day, it has lived until it warms enough to stay outside. By fall it looks marvelous again. Hopefully it comes through this winter as it has the past few.

    • January 29, 2013 10:14 pm

      Harriet, Thanks for these helpful tips. Finding a cool spot for it will be the biggest challenge. (Maybe one of those drafty window ledges with the cyclamen.)

  4. Laurrie permalink
    January 26, 2013 11:30 pm

    I am growing Rosmarinus ‘Madeline Hill’ out in an open sunny, yard planted in the soil in my northern Connecticut garden. Winter temps here get to the single digits, zero one night, but mostly our lows are 5 or 6 degrees F during cold snaps like this week. It is not covered. It’s been out there several winters now and doing well. ‘Madeline Hill’ and a more upright one called ‘Arp’ are cold hardy to zero. That won’t do in your Maine garden if you get below zero temps, but in my zone 5 /6 spot this cultivar is hardy!

    • January 29, 2013 10:16 pm

      Laurrie, I had no idea there were named cultivars of rosemary; I don’t remember ever seeing any being sold that way. Maybe this one is doing so well not just because we had an exceptionally mild winter last year, but because I happened to get a more cold-hardy variety. It still won’t help in my Maine garden, though, which regularly gets overnight lows between -15 and -20F.

  5. January 27, 2013 8:05 am

    I hope your rosemary is ok. I grow some rosemary in a pot and have successfully brought it inside and overwintered it for the last three years. Unfortunately this year it was a bit neglected and died when the soil became too dry. I am hopeful that I can succeed again with a fresh plant.

    • January 29, 2013 10:19 pm

      Rachel, Have you kept yours in a cool spot when you’ve successfully overwintered it? I don’t think adequate watering will be a problem for me; I normally just water all my plants once a week. When I see the size that this plant grew to by its second year, though, I think I need to consider bigger pots than I’ve used in my past unsuccessful attempts at overwintering indoors.

      • February 17, 2013 10:16 am

        Sorry for the late reply. My rosemary was overwintered on a windowsill so it was cool at night and warmer during the day.

  6. Helen Johnstone permalink
    January 27, 2013 1:01 pm

    I have a large prostrate rosemary and that has coped with -19C for days on end for two winters. Here in the UK we have fleece which is a fine fabric that you put over plants, it protects from them from frost but allows rain etc through.

    • February 2, 2013 10:48 pm

      Helen, I had no idea it got this cold in England. This is the kind of overnight temperature in winter that is typical in my Maine garden. I think the difference is that we have these temperatures for months, rather than days, on end. I need to check out what is available here to protect plants from winter conditions.

  7. January 27, 2013 2:00 pm

    In the UK, the only trouble I’ve had with rosemary is if is becomes too wet (soggy soil) in winter, the roots quickly rot and the plant dies. My rosemary is outside, south-facing and in the ground. I must admit that I hadn’t given any thought to its winter hardiness because it just doesn’t get cold enough for long enough for it to be a problem. I don’t know how I would protect it from your winter temperatures but I do have a temporary “winter” greenhouse for my more tender (barely frost-resistant) plants and despite having recently had two weeks of sub-zero temperatures, they’re looking OK. You might need to do something similar?

    • February 2, 2013 11:25 pm

      Sunil, I have read your posts about your greenhouse with great interest. I’m hoping that the addition I’m planning for my house will include an enclosed porch with a southern exposure, and that may be just the place for a greenhouse similar to yours.

  8. January 27, 2013 2:16 pm

    My house is too warm to overwinter rosemary – it becomes etoliated. Last summer I grew my new rosemary plant in a pot, and when temps dropped in the fall, covered it with a pillowcase on cold nights. But then it got *really* cold and I was afraid the pot would crack, so I moved it into the garage which usually stays above freezing. The plant does not get much light and I have not been watering it, but it seems fine. Fingers crossed it stays that way. Good luck with your rosemary.

    • February 2, 2013 11:32 pm

      I’m not sure I have a cool enough place for this indoors, either — although my drafty window ledge might work. I hope your garage solution works out.

  9. January 27, 2013 2:38 pm

    Jean, I really hope your rosemary survives, I would advice you to use straw surrounding the ground and the plant. I have four in my garden, three of them planted in fall so still small and one I inherited and is flowering because the fall and beginning of winter were very mild, let’s see how they continue now that we are in the coolest moments of the year. Fingers crossed that you will enjoy your rosemary in spring!

    • February 3, 2013 12:14 pm

      Lula, Thanks for the tip about the straw mulch. I may try that next year. In a few weeks, we are likely to be past the danger of extremely cold overnight temperatures; so if I can be vigilant about protecting my rosemary on cold nights for just a little bit longer, I’ll get to see how big it grows in year three!

  10. January 27, 2013 2:53 pm

    Lovely to see rosemary overwintering outdoors, Jean. It’s somewhat marginal in my former garden, and with the frigid winter temperatures we’ve had for nearly a week, I’m thinking it would have to winter indoors here, too. I was at a friend’s yesterday, stopped in mid conversation, and begged him to water his indoor rosemary plant. :-)

    • February 3, 2013 12:16 pm

      Hi Jodi, Watering indoors is not usually a big problem for me. I’m one of those people who thrives on schedules and routines, so I water all my houseplants on the same day every week. I think if I can calibrate the size of the pot and the amount of water each week so that the soil stays moist but doesn’t get soggy, I should be fine.

  11. January 27, 2013 5:15 pm

    I do hope this works, rosemary is such a beautiful plant when it grows big (and has pretty flowers to boot). I wish wish wish I could grow rosemary year round but like you I have to content myself with new seedlings from the nursery each spring.

    • February 3, 2013 12:19 pm

      Marguerite, It’s interesting that Jodi could sometimes overwinter rosemary in coastal Nova Scotia, but that temperatures are too cold in coastal PEI. I think your winter conditions are very similar to mine in Maine (although I’m about 25 miles inland, just far enough not to get the moderating effects of the water).

  12. January 27, 2013 7:39 pm

    Good luck Jean. I have smaller rosemary plants in pots but I had to put them under grow lights and on heat mats so they now survive the winter inside.

    • February 3, 2013 12:21 pm

      Donna, I’m going to have to do some research on the appropriate temperature range for these plants indoors. It’s interesting that some worry about keeping them cool enough (note Harriet’s recommendation of a 50 degree room) while you worry about keeping them warm enough.

  13. January 28, 2013 12:18 pm

    I love the nightgown-as-plant-cover, I must say. In my climate, rosemary overwinters with no problem, so I have the reverse problem that you have – too much rosemary to use up, even when I make roast chicken and rosemary potatoes with some frequency. I guess I need to add white bean stew to the menu…

    • February 3, 2013 12:29 pm

      Sarah, Hey, whatever works! :-) I am not worried about using up all the rosemary; I just like the shrub-like proportions it is starting to take on outside. This is making me realize that if I’m going to grow it in a pot for my Maine garden, I need a big pot and a location (perhaps by a patio on my imagined new front garden) where it can be a substantial presence.

  14. January 28, 2013 7:55 pm

    Jean, I wish your rosemary well! Your nightie is the cutest cover I have see. If the rosemary doesn’t survive, it is certainly worth replanting, even if only as an annual. The rosemary in my garden has survived for a number of years and has grown to a substantial size, though we sometimes do get temps below 20, though briefly. Since you tucked your plant in after only one night of letting cold in around the edges, I am hopeful your rosemary will survive.

    • February 3, 2013 12:33 pm

      Deb, Up until now, I have always bought a new seedling every year and treated it as an annual. But the size that this plant got to in its second year in the garden was a revelation! From what I’ve been reading, it seems as though many varieties of rosemary will survive well below 20F — maybe down to 0F or even a little below — with a little protection. I’m glad you liked my impromptu plant cover; it was a nice bit of serendipity that the recently retired nightie had a garden-appropriate spriggy floral print :-)

  15. January 28, 2013 11:38 pm

    Hi Jean, i guess rosemary is really for the tropics as mine has been growing there for a few years now. However, it is not growing as luxuriously as those i see in subtropical setting. Morever, ours doen’t flower like their counterpart in your part of the world. In my case, i don’t use it for cooking as i am not very particularly keen on herb cooking, but i love its scent more than any herbs. I touched them with my palms and get the sweet scent. Even if they dont flower here, at least i don’t have to put extra caring like you during your winter.

    • February 3, 2013 2:24 pm

      Andrea, From what I’ve been reading, rosemary is a Mediterranean plant — so I can see how your tropical wet season/dry season pattern would be to its liking, even if your climate is maybe a little too hot for it to really thrive. I, too, love the scent. The gloves I was wearing out in the cold when I was trying to cover it seem to now be permanently imbued with that scent.

  16. January 29, 2013 3:55 am

    Is this what is meant by ‘airing your dirty linen in public’, Jean?! :) Hope you are successful anyway.

    • February 3, 2013 2:26 pm

      Cathy, I was about to protest that the nightgown was clean; it had been through the laundry before it was retired to the rag bag. But I guess now that it’s been draped over the plant and tucked up against the soil, it really does count as dirty linen airing in public :-|.

  17. January 31, 2013 7:51 pm

    I hope it comes thorough! It’s frustrating to have to replace a plant every year due to weather. My rosemary overwinters just fine but I’m several zones warmer than Maine. :) rosemary roots very easily in case you want to start a new plant inside. You don’t even need a rooting hormone. Just stick a sprig in water and put it somewhere warm.

    • February 3, 2013 2:28 pm

      Tammy, Thanks for this tip. I’m going to cut some sprigs and put them in water to root. Not only will this provide insurance in case I lose this plant (although I don’t think I will); but I can’t plant the rooted cutting in my Maine garden instead of buying a nursery seedling.

  18. February 3, 2013 9:48 am

    Jean, good luck with your Rosemary. I have never tried it, often tempted as it would make a good alternative to Lavender which takes a beating from the Winter some years. Here in Aberdeen which is on the East Coast of Scotland in spite of having raw weather that seeps right into your bones the temperature seldom drops below 20f/-07c./ More often the temp sits between 35f and 42f in winter and from June till September the daytime can range from 55f to 70f on occasions a bit higher and sometimes even cooler.-

    • February 3, 2013 2:31 pm

      Alistair, I envy you your lavender, which I would love to have in Maine, but which tends not to be happy with either the cold or the acidic soil there. I’m amazed by how mild your climate is.

  19. February 10, 2013 4:14 am

    Hi Jean, I wrote a longer reply but something went wrong….anyway, I was also going to suggest horticultural fleece. I also recommend not living with a cook if you want to preserve your rosemary.

    • February 19, 2013 9:20 pm

      Claire, Helen (Patient Gardener) also suggested this. I did some research around the web and finally found that this product is sold in the US sometimes as “garden fabric” and most often as “floating row covers” to put over crops in spring to warm the soil faster and protect young seedlings from being munched on. I’m going to look into getting some. Thanks for the suggestion.

  20. February 24, 2013 10:43 am

    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 topgrowth.

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