By Peggy Riccio
Plant propagation is just a fancy word for making more plants from what you have. I love to propagate the plants in my garden. To me, it is magical that an entire shrub can be created from cutting six inches off the stem. Taking stem cuttings is an easy way to make more shrubs to fill in gaps in the garden or to share plants with gardening friends.
One shrub that I often propagate via stem cuttings is rosemary (Rosmarinus officinalis). The best time to do this is in early summer when new spring growth starts to become semi-woody but is still supple enough to root easily. The rosemary plant’s stems must have new growth but be firm enough to snap. If you can grasp the end of the branch about 6 inches from the top, bend it at a 90-degree angle and it snaps and breaks off, it is ready.
I cut from the tip of the stem, about 5-6 inches down, ensuring that there are several nodes. The node is the point where additional stems/branches arise but also the point in which there is a higher chance of root stimulation. I first cut above the node on the shrub and then make a second cut on the stem, just under the last node. I remove the bottom leaves and insert the cutting into water, then a commercially prepared rooting hormone, and then in the pre-moistened potting mix, about one-inch deep, in a small plastic pot or container. The cut end of the stem is just dipped into the rooting hormone – only the end needs it.
I, then, cover the plant with a gallon size zipper top plastic bag, blow air into the bag to inflate it as much as possible, and close it. I put my cuttings in a cardboard box or lid and then place this on my deck under the eave of my house for shade. The box prevents the bags from blowing over or away. The next day, I check the bags to make sure they have condensation inside. If you see condensation, then you know it has enough moisture. If you do not see condensation, open the bag, take the plastic pot/container out, water it, and put it back in the bag.
After a few weeks, I check rooting progress by opening the bags and gently pulling the cuttings to see if there is resistance. If the cuttings have rooted, I start to open the bags a little bit, a few hours a day, still in the shade. If I open the bags and the plants wilt very quickly, I know they have not produced enough roots yet. Successful rooters will keep their color in the leaves; unsuccessful plants will fade or collapse. I always cut more than I need, because there will be some that will not “take.” It is a numbers game, much like growing from seed.
Once the cuttings have rooted and can survive without the bag, I transplant them to a larger pot. I often give these away to friends, but for my garden, I let mine grow on the deck and gradually expose the plants to full sun. I do not plant these cuttings in the garden bed until the fall. The larger the plant, the more roots, and the more likely it will be successfully transplanted in the garden bed. Plus, the cooler fall weather is better for transplanting than the summer’s heat.
When you propagate by stem cuttings, you must always use clean materials to prevent a fungal infection. It is best to use clean plastic containers with drainage holes. Sterilize them with a 10% bleach solution of one part bleach and nine parts water, rinse, and let dry. Sterilize cutting tools, pruning shears, or garden snips with rubbing alcohol before you make the cuts.
Use a bagged potting mix specially formulated for starting seeds such as Pro Mix, Jiffy, or Burpee. The water for watering the potting mix and for dipping the cutting should be “clean,” i.e., tap water, not water collected from rain (gray water). The bags should be new and unused.
The best time to take stem cuttings is in the morning when the plant is “turgid” (turgid refers to cells or tissues that are swollen from water uptake). Make sure you have everything ready and available; you cannot afford to let the cuttings sit and wilt while you bleach the pots. Have fun with this, and always do more than you need so you get the amount you want. Give the extras to friends!
Photo Credits: 1) Cutting dipped in rooting hormone; 2) Cutting in a plastic bag; 3) Rooted cutting; 4) Potted up cutting. All photos courtesy of the author.
A horticulturist in Virginia, Peggy Riccio’s website, pegplant.com, is an online resource for gardeners in the Washington, DC metro area. Currently, she is the chair of the Potomac Unit of The Herb Society of America.