As a commercial herb grower, I’ve growled more than once that home gardeners can’t expect to successfully propagate herbs from cuttings without spending a lot of money for equipment, but I repent. I’ve found a simple, inexpensive, effective way to root cuttings of many herb varieties; it’s probably the same method that your grandmother used. All you need is a glass of water and a windowsill.
I spent a recent summer experimenting with rooting cuttings of more than a dozen herb species in water, and I can tell you that this method, in some instances, will root cuttings as fast for you as my expensive automated propagation gadgets can for me. This method almost totally eliminates plant stress, which otherwise slows rooting, and it avoids some of the wilts and rots that plague home gardeners when they try to root cuttings in a soilless medium. (“Growing Herbs from Stem Cuttings” in the February/March 1993 Herb Companion addresses some of the difficulties.)
In comparing new and old gardening techniques, I find that traditional methods sometimes are at least as good as modern ones, but Grandma may not have told you all you need to know to make her way of rooting cuttings work as well for you as it did for her.
Plant Propagation: Principles and Practices, by Hudson T. Hartmann and Dale E. Kester, a text used by many professional propagators, states that water can be used to root cuttings of easily propagated species. I’ve found that many herbs fit that category.
Most of the herbs I tried rooted within two weeks or less: mints (Mentha ¥ piperita ‘Mitcham’ and M. spicata) in seven days, basil (five varieties of Ocimum basilicum) in five to ten days, patchouli (Pogostemon cablin) in ten, pineapple sage (Salvia elegans) in eleven, and lemon verbena (Aloysia triphylla) and a cultivar of rosemary (Rosmarinus officinalis ‘Arp’) in fourteen days. (Although basil is usually grown from seed, some new cultivars, such as Aussie Sweetie, Mulberry Dance, and Holly’s Painted, to name a few, either don’t flower well or don’t come true from seed, so rooting their cuttings is the most reliable way to propagate them.)
Some herbs were less successful. Scented geraniums took twenty-six days to root vigorously; an oregano (Origanum ¥ majoricum) took about as long, but the roots were weak and sparse. Fruit sage (S. dorisiana) took nearly four weeks. The two lavenders I tried, Lavandula angustifolia ‘Tucker’s Early Purple’ and L. a. ‘Sharon Roberts’, rooted in a little over six weeks, but only a small percentage of the Tucker’s Early Purple struck roots, and weak ones at that.
A few of the herbs didn’t respond at all. French tarragon (Artemisia dracunculus var. sativa), thyme (Thymus vulgaris ‘Provencal’), balm of Gilead (Cedronella canariensis), and myrtle (Myrtus communis) either rotted or had failed to root after two months. Two cultivars of common sage, S. officinalis ‘Rubriflora’ and S. o. ‘Albiflora’, did not root at all. (All of these can be propagated by division or are fairly easily rooted in a peat-based medium that is misted frequently.) I found that not all varieties of the same herb species rooted with the same speed or vigor, but this is also true with other propagation methods.
Some techniques that improve the rooting of cuttings in other media don’t work when used with water. Scented geraniums, for instance, often root better when they are cut in the evening and allowed to sit in a plastic bag overnight to allow the wound to callus before they are stuck in a soilless medium. The cuttings that I treated this way did not root at all in water, while untreated ones did well. I knew that wounding cuttings of sweet bay (Laurus nobilis) by scraping either side of the stem helps them strike roots in a peat-perlite medium, but this didn’t seem to make any difference in water.
The response of bay cuttings surprised me. Even under the most favorable conditions—with root-zone heating and intermittent misting—only 50 to 70 percent of my woody bay cuttings will root in a soilless growing medium after six to eight weeks. I tried them in water, and they just sat in their Styrofoam cups without striking a single root. At the end of two months, the stems didn’t appear callused, swollen, or ready to sprout roots, but the part of each stem that was under water was covered with wartlike nodes. I nearly gave up on them, but instead I moved them to 2 1/2-inch pots containing my usual growing medium. Within a month, all were nicely rooted and growing well with no special care. A 100 percent success rate with bay cuttings was a first for me.
Although it’s quite possible to throw a cutting in a glass of water and have it root, you’re likely to have greater success with a wider range of cuttings if you pay attention to a few details. Take cuttings from plants that are in vigorous growth outdoors. Indoor plants with soft, thin stems are unsuitable for rooting; outdoor plants that are dormant or entering dormancy are often difficult or impossible to root. Generally, the best time for rooting cuttings is in spring, but I have had success with cuttings taken all through the growing season. Nonflowering stems are the best choice; remove any flower buds from other stems.
Choose plants that are free of diseases and insects. Take cuttings in the same way you would if you were rooting them in a soilless medium. As a hedge against failure, I like to cut several stems of each plant, putting them all in one container unless they seem overcrowded. Cut each stem about 3 to 4 inches from the tip with a sharp pair of scissors or knife and remove the lower leaves on the part that will be submerged. Fill a glass, short jar, Styrofoam cup, or other container with water to just below the first leaves; at least the top third of the cutting should extend above the rim. Place the containers where they will receive plenty of bright light but no direct sun; I rooted my cuttings on the kitchen windowsill.
Changing the water every day is the key to success with rooting in water. It keeps the water free from bacteria that can cause stems to rot.
As soon as the cuttings have roots 1/4 to 1/2 inch long, they are ready to transplant into pots; don’t let them grow into a dense tangle. For growing medium, I recommend using a peat-based mix. You can purchase a prepared mix such as Pro-Mix BX, or make your own by mixing equal parts of peat and perlite and adding the equivalent of 1 teaspoon lime per 6-inch pot; dampen the mix with a half-strength fertilizer solution.
I have read so often that cuttings rooted in water do not transplant or grow well, but I have never had any problems as long as I first transplant them into a pot so that they can become established plants, a system I also follow with cuttings rooted in a soilless mix.
Place the potted cuttings in a sunny window or a few inches below fluorescent lights or in a greenhouse. The heat in my greenhouse (often over 100°F during the day) made my cuttings grow quickly. Pinch the stem tips to promote branching after you pot them. Continue to fertilize with a half-strength fertilizer solution every fifth time you water.
Let the cuttings grow on for several weeks before transplanting them to a larger pot or into the garden. The roots should be visible and hold the root ball together.
Rooting cuttings in water is a handy propagation technique for use throughout the growing season, but it is especially useful in late summer when it’s time to start new plants to grow indoors over winter. With luck and a little attention, you’ll have windowsills filled with rooted cuttings to enjoy during the cold months or to set out next spring, as well as some to share with friends.
Tom DeBaggio is an herb grower in Arlington, Virginia, where he owns a seasonal retail greenhouse. This article is adapted from a chapter in his book, Growing Herbs from Seed, Cutting, and Root, which will be published in November by Interweave Press.