You may have seen pots of rosemary (Rosmarinus officinalis) pruned to look like Christmas trees in a local garden center or even a supermarket or box store. Since rosemary leaves are very needlelike, their delicious aroma has an almost coniferous smell to it, and the plants have been trimmed to take on a pyramidal shape, the plant could indeed pass for a small Christmas tree… but one with edible “needles”. What a great idea as holiday season decoration!
Except that… very few of the rosemary trees sold in November or early December make it as far as Christmas. In general, few people get more than about 2 weeks of use out of one before the plant dies. And many of those being sold are already in very poor shape before they even leave the store!
The Pros and Cons of the “Rosemary as a Houseplant”
You should know in advance that the rosemary is no philodendron or dracaena. In fact, it actually makes a rather finicky indoor plant.
At the holiday season around the Mediterranean Sea, where it grows in the wild, it would be experiencing full sun, cool days (rarely above 60˚F/15˚C) and cold nights: often just above freezing. It therefore finds our homes very dark and very hot. Plus indoor air is at its driest in the winter while it’s at its moistest in the plant’s natural environment, with a relative humidity that usually stays above 60% whereas in many houses it’s closer to 10%. So your Christmas rosemary is under considerable stress.
That said, if you choose your plant well and place it in the right spot at home, it is possible to not only keep a rosemary Christmas tree in good shape until January, but even throughout the winter.
Choosing a Rosemary Christmas Tree
The most important factor in your plant’s future survival is choosing a healthy one, because rosemary is not a plant that readily forgives mistreatment.
Unfortunately, the rosemary plants sold for the Christmas market are often already in poor condition before you buy them. If the plants you see are have browning, crunchy leaves that drop off when you run your hand over them or they look sparse and their potting soil is strewn with fallen leaves, leave them in the store: they are probably already dying if not dead.
Even if the plants’ potting soil is simply dry to the touch in the store, that’s a bad sign: the plant is perhaps already in distress, but may not yet be showing it. The soil should be moist, but not soggy, when you buy the plant.
Ideally you would buy your rosemary tree as soon as it arrives in the store. That is doubly true if you see it in a supermarket or a box store (garden centers, at least, know how to keep their plants healthy while waiting for them to sell!). You can assume freshly delivered plants, at least, have not yet begun their decline!
If it is less than 40˚F (5˚C) outside when you buy you plant, make sure it is carefully wrapped before you take it home. Again, supermarkets and box stores don’t know much about protecting plants, contrary to garden centers. You won’t want any of the leaves to be exposed to cold, so the plant needs to be completely covered. Often that means placing the pot in one bag and covering the top of the plant with a second bag. Accept nothing less!
Finally, don’t leave the plant in a cold car while you continue shopping. Return home with your new plant without delay.
If you want your rosemary tree to last a long time, don’t set it on a table in the middle of warm room like you might a poinsettia. It should go directly in the sunniest, coolest place you have, almost certainly near a large window and somewhere temperatures drop to less than 60˚F (15˚C) at night. Place it on a humidity tray or turn on a humidifier to increase the air’s relative humidity.
You’re thinking of decorating your rosemary tree for the holiday season? Go ahead and do it: that won’t harm the plant… as long as you use small, light ornaments that won’t snap off branches and LED lights that don’t give off heat.
If the air in your home is hot and dry, you’ll find that your rosemary tree will dry out very quickly and may need to be watered more than once a week. If the air is humid, it won’t need such frequent waterings. In both cases, though, wait until the soil is dry to the touch, then water thoroughly, moistening the entire root ball. But don’t leave the roots soaking in a saucer of water either.
There is no use fertilizing your plant during the Christmas season: it will be in “survival” mode – just hanging on rather than truly growing – during the winter and won’t be able to use the minerals you provide it.
Watch out for spider mites (read When Spider Mites Invade for more info) and, if you detect any, give the foliage a good shower to remove both the mites and their webs.
Unfortunately poor air circulation indoors over the winter sometimes leads to powdery mildew, which looks like a dusty white powder on the plant’s “needles”, almost as if they were covered in really fine snow. It’s actually a fungal disease. Try giving the leaves a thorough shower to knock off the white spores, then spray with neem oil to keep the disease from recurring. You’ll probably have to prune off sections of dead leaves too. Rosemary will recover from powdery mildew, but it often leads to a loss of symmetry that is difficult to cure.
Spring and Summer Care
When the days lengthen noticeably, normally in March, you’ll see your rosemary start to produce fresh leaves. This is the ideal moment for repotting it into a larger container. It was probably growing in too small a pot when you bought it (growers do that to reduce transportation costs: smaller pots mean lighter plants and lighter plants are cheaper to transport), so repotting is certainly due. Any potting soil for indoor plants would be suitable.
You can fertilize lightly (rosemary is not a “greedy” plant when it comes to minerals) as soon as its growth resumes. Any fertilizer you have on hand would be appropriate: apply it at the frequency recommended on the label, but only at 1/8 of the recommended rate.
New growth also means it’s time to begin pruning. Your plant’s pyramid shape isn’t its natural habit. Although come cultivars are more upright than others, rosemary still tends to remain more of a bushy or spreading shrub than a conical Christmas tree. Prune it to shape, cutting back overly-long branches. Repeat every 3 or 4 weeks throughout the growing season. Obviously, any bit pruned off can go straight into the cooking pot!
When summer comes, put your rosemary outdoors. Start first in a shady spot, then partial shade, then full sun, all over a 2 to 3-week period. Do note that outdoor plants dry out much more quickly than indoor plants, especially those growing in pots, so keep a watering can handy. The goal is the same: the soil should always be slightly moist, never either completely dry or soggy.
Note that pruning rosemary to maintain a pyramidal shape means you’ll be pruning off any flower buds and therefore it’s unlikely yours will ever bloom. If you let your rosemary resume its “natural shape”, however, it may produce its attractive little pale blue flowers during the summer.
When Fall Comes
Only in the mildest climates (zone 9) is rosemary going to be fully hardy outdoors, especially container-grown plants, so you’ll have to bring your plant back indoors come September. Place it in a sunny, cool spot and repeat the recommendations given in Home Care above, notably as concerns watering as needed and increased air humidity.
There you go! Yes, rosemary is a capricious plant when grown indoors, especially when it’s pruned to look like a Christmas tree, but with good care, you can keep yours going for many years.