Jennifer Schultz Nelson
Extension Educator, Horticulture
Most of us only ever see rosemary as an herb for sale each spring and summer. In recent years I've noticed more and more plants for sale at holiday time, typically trimmed into topiary trees or wreaths.
The typical young plants we use in our gardens each year are rather green and succulent, but mature rosemary is a woody shrub-like evergreen plant. Plants purchased during the holidays usually show some woodiness, because they are older plants. It takes time to grow and shape them into topiaries.
Part of the lure of growing rosemary is its wonderful scent. The needle-like leaves release a pine-like fragrance whenever they are brushed or crushed. It is a great addition in cooking, particularly with roasted meats.
Rosemary is native to the Mediterranean region, where it grows into large bushes up to four or even six feet tall. The key to successfully growing rosemary is trying to reproduce its native conditions.
In its native land, rosemary is used to cool moist winters and hot dry summers. A word of caution: either one of these environments taken to an extreme will spell the end for your rosemary.
This time of year, as temperatures begin to dip, I receive a lot of questions on what plants can be successfully overwintered indoors. Rosemary is a plant people always ask about. I'll admit, I have killed more than a few innocent rosemary plants by trying to grow them indoors over the winter. There is a fine line between the cool moist conditions that encourage plant health and the cool moist conditions that encourage root rot and plant death.
I have erred on the side of too dry as well. Plants in the ground outdoors in the summer don't like to be extremely dry either, but in pots indoors in the winter they are even more sensitive. Letting the soil dry between waterings is a good idea, but allowing the soil to become dry as a bone is not. In my experience, letting the plant get overly dry, coupled with low humidity in our winter homes is an invitation for pests like spider mite that thrive in dry conditions.
I have had a few plants survive well over the winter. Some keys to success in growing rosemary indoors are: 1) Use a well drained potting mix, 2) Keep the soil moist, but not soggy and 3) Place your rosemary where it receives as much light as possible.
When you are successful at overwintering your rosemary indoors, you may be rewarded with a show of blue, pink or white flowers in the early spring for most cultivars, later in the summer for others.
I love to plant rosemary in my garden outdoors, but one of the drawbacks to growing rosemary in our area is its limited hardiness. Typically, rosemary is reliably hardy only in Zones 8-10. There are a few cultivars, such as 'Arp' and 'Hill Hardy' that claim that with added protection of mulch, they are hardy down to Zone 6.
I planted one of the more "hardy" rosemary cultivars in a protected little niche right up next to my house, thinking since this method seems to work for my mums, it would surely work for rosemary. No such luck.
About the best method I've seen for overwintering rosemary in this area comes from the U of I Extension Master Gardeners in Sangamon-Menard County. They use the product called "Wall o' Water" typically used to start tomatoes in the garden extra-early to overwinter the rosemary in their demonstration garden.
If you are not familiar with the "Wall o' Water", it is a flexible plastic cylinder with plastic chambers built in it that is placed around the plant like a tomato cage. The chambers are filled with water, which provides enough insulation to keep the plant inside at least a few degrees above the outdoor temperature.
The Sangamon-Menard Master Gardeners also add a healthy dose of fall leaves in with the rosemary plant as additional protection. They have some of the largest and most beautiful rosemary plants I've ever seen in this area.
Rosemary has had medicinal uses throughout history, curing everything from depression, to infections and wounds. Legend has it that rosemary improves memory—it is often touted as the herb of "remembrance" and has been used symbolically in weddings and funerals.
One of my favorite rosemary legends I read about says that when a rosemary plant flourishes in the garden, it means that the woman wears the pants in that family. One centuries-old writer described this legend and wondered how many rosemary plants men have secretly injured in order to destroy evidence of their lack of authority in their household. I don't know if this legend is true, but to be on the safe side, ladies, keep your rosemary growing strong!