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. Now that spring is past and summer is approaching, it is a good time to take softwood or semi-hardwood stem cuttings of some of my favorite shrubs. The terms softwood and semi-hardwood relate to the time of year the stem cutting is done (another stage, hardwood cutting, is done in the winter when the plant is dormant). A softwood cutting is usually done May through July here in the Washington DC metro area. This is the point where a deciduous shrub’s new spring growth starts to become semi-woody but still supple enough to root easily. The shrub’s stem 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. Depending on the plant and your comfort zone, it may not be necessary to use a rooting hormone.
The semi-hardwood or semi-ripe cutting is done from June through August. This is when the new growth has stopped elongating, the bark has toughened, and the bright color is now dark. The “soft” wood has now become “woody. This cutting can be done if one missed the softwood stage. You use the same technique as a softwood cutting but you make your cut lower down on the stem, so the cut is in the woody area. It may be necessary to wound the end of the cutting by removing a one-inch long strip of bark at the base to stimulate root production. This type of cutting could take longer to root than softwood, maybe 2 months, but less likely to fail from wilting. However, you should use a rooting hormone.
For both types, I cut from the tip of 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 roots 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 rooting hormone (if I am going to use one), and then in the pre-moistened potting mix, about one-inch deep.
For small shrubs, I use a small plastic container and cover the plant with a gallon size Ziploc plastic bag. I blow air into the bag to inflate it as much as possible and close it. I always write the plant name on the bag and I write down the plant name and date in my gardening journal.
For large shrubs, such as an oak leaf hydrangea, I have used an old glass fishbowl, covered, or the large plastic containers of Twizzlers you buy for the office candy bowl.
I have a deck, so I place my cuttings in a cardboard box or lid under the eave 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 container out, water, and put back in the bag.
Depending on the plant and time of year, it will take a few weeks to a few months for the stem cuttings to root. Check by opening a bag and gently pulling the cutting to see if there is resistance. If the cutting has rooted, I start to open the bag a little bit, a few hours a day, still in the shade. If I open the bag and the plant wilts very quickly, I know it has not produced enough roots yet. Successful rooters will keep their color in their 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 stem cutting can survive without the bag, I pot it up to a larger pot. I gradually expose the plant to full sun. I do not plant it in the garden bed until the fall. The larger the plant, the more the roots and the more likely it will survive the transplant. Plus, the cool fall weather is better for transplanting than the summer’s heat.
Secret to Success
That is the technique for stem cuttings; however, the secret to success is understanding the concept of transpiration. Transpiration is the loss of water from a plant in the form of water vapor. A plant is always taking up water through the roots and losing it through the leaves. Water is continuously evaporating from the surface of leaf cells. The rate depends on the dryness of the air — the drier the air, the faster the transpiration. The higher the temperature, the brighter the light, and the faster the speed of the wind, the drier the air and the quicker the plant loses water.
When you cut a stem, you have eliminated the roots and the plant’s capacity to replenish water. To prevent the cutting from drying out, you want to 1) minimize transpiration; and 2) encourage the cutting to root as fast as possible. You can reduce transpiration by putting it in a place with moist air so the loss is minimal. However, too much moisture and too little air circulation will result in a fungal growth. So you have to strive for a balance between a moist environment for the cutting and not too moist that fungus grows and the cutting rots. Also, you want to encourage root growth which is why a commercially prepared rooting hormone is used with the slow rooters.
If the plant is a quick and easy rooter, you will not need a commercially prepared rooting hormone. Plants have hormones that aid in the formation of roots called auxins. The amount of auxins may vary in plants throughout the year and within the plant. If you do not know if it will root easily or you want to increase your chances of a quick root, you can use a commercially prepared rooting hormone. In other words, it does not hurt to use a hormone. Commercially prepared rooting hormones are comprised of synthetic auxins called indolebutyric acid and/or naphthaleneacetic acid. Usually a lower percentage of the synthetic hormone is required for herbaceous softwood cuttings (1,000 ppm or .1 percent) while a higher percentage is necessary for semi-hardwood to hardwood cuttings (3,000 to 8,000 ppm or .3 percent to .8 percent). Examples are Bontone II Rooting Powder, a white powder; Miracle-Gro Fast Root, a white powder; Dip ‘N Grow, a liquid; and Clonex, a gel. When you use this, put a small amount in a little container so you are not dipping the stem cutting into the original container (thus contaminating).
Rules to Follow
There are a few rules when making cuttings but the primary rule is cleanliness. To prevent a fungal growth, use clean materials. It is best to use clean plastic containers with drainage holes. Sterilize them with a 10 percent bleach solution of one-part bleach and nine parts water, rinse, and let dry. Wear plastic gloves and old clothes when you work with bleach. While you are at it, sterilize your your pruning shears or garden snips with the bleach before you make the cuts.
Use a bagged potting mix especially 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 or unused and if you use larger propagation chambers such as plastic shoe boxes, plastic storage containers, glass terrarium/fish tanks with lids, just make sure they are clean.
The best time to take stem cuttings is in the morning when the plant is turgid. Make sure you have everything ready and available; you cannot afford to let the cutting sit and wilt while you bleach the pots. Have fun with this. I find it is best to take several cuttings from one shrub so if one does not take you don’t get disappointed. Experiment, take notes, and discover the magic of plant propagation!