Extension Educator, Horticulture
Until the 20th Century, the herb rosemary was a very popular Christmas plant, along with holly and mistletoe. Why rosemary fell out of favor as a Christmas plant is unclear. However over the last few years, it has made a comeback in wreathes and as holiday decorated topiary. An offering of rosemary signifies love and remembrance, which is not a bad sentiment this time of year. And a sprig in your stew is quite tasty too. Rosemary is fairly easy to grow outdoors in the summer. However the problem is keeping that lovely rosemary alive over the winter.
Rosmarinus officinalis is a perennial evergreen shrub hardy to zone 7. In its native Mediterranean home it can reach six feet tall. I have had one rosemary plant for ten years now and she has reached a huggable size. Nothing will cheer you quicker on a dull dreary Illinois day than hugging old rosemary. The fragrance of pine will fill the air.
Most homes are just too dry and too warm in the winter to suit rosemary. She likes it cool and moist. After all her native lands are the rocky hillsides over looking the Mediterranean.
In winter when she is fairly dormant, she needs a cool brightly-lit spot in a home. If you want rosemary to live indoors, set the thermostat down to about 63–65°F. Also provide plenty of light with a south or west exposure. Low light will produce leggy growth.
A garage where the temperature doesn't drop below freezing would also work given there is plenty of light or supplemental light is provided.
If you read rosemary care instructions, it will often say let dry between waterings. Good advice to a point since rosemary can suffer if soil remains waterlogged. Rosemary requires excellent drainage. Remember that rocky hillside. Letting it dry between waterings does not mean it's ok to let it sit dry for a week as we can with some succulents like jade plants. My experience has been as soon as the soil dries, it's time to water. I try to never let it sit dry for more than a day. I also have my rosemary in soilless mix and a well-drained clay pot so overwatering is less likely.
Around the first of May rosemary goes outdoors where she sunbathes happily on my patio until fall. I have had much better luck leaving her in the pot rather than trying to dig her up each fall. The pot could also be sunk into the ground over the summer.
Rosemary shouldn't be subjected to temperatures below 10 degrees F. Cultivars such as 'Arp,' 'Athens Blue Spire' and 'Madalene Hill' are reported to be hardy to zone 6. With protection they may survive a central Illinois winter.
In the fall I let my rosemary remain outdoors until about the end of October. Then she goes into an unheated porch for a couple of weeks before I finally bring her indoors. Some recommend bringing the pot indoors before the furnace is turned on.
Rosemary adds fragrance to the home as well as a pleasing flavor to cooking. Many new cultivars have been selected for their fragrant oils and ornamental appeal. Once you understand rosemary's needs, she can be a long-lived companion.
Stop by our office for an excellent article on rosemary by U of I Extension herb and vegetable specialist, Chuck Voigt.
Interested in herbs? Be sure to attend these two events.
Herb Growers conference - for those interested in the business of herbs.
Herb Day - for the novice to the well-versed a full day of programs by nationally known speakers including a retail shopping area. Both events are at the Holiday Inn in Urbana. For info, call 217-333-7738.