by Leslie Cox; Thursday; September 6, 2018
A relatively easy way to propagate new plants is by rooting stem cuttings. Success is better achieved by using a good potting medium, a sharp clean cutting tool, and a rooting hormone.
Types of stem cuttings
- Softwood are new stems developing in spring on existing branches. They are typically referred to as “this year’s growth” and taken in spring and early summer…late May through June.
- Semi-hardwood are stems which are nearly mature. These are the type of cuttings taken in mid-summer…mid-July through early August.
- Hardwood are stems which are fully mature. These are the type of cuttings taken in late summer and early fall…mid-September through early October.
Most plant species root well from any of these stem types, although some shrubs and trees will root better from semi-hardwood and hardwood stem cuttings. And of course, there are many perennials who do not develop hardwood stems at all.
Taking the cutting
First order of business is to select a healthy plant. This plant will provide a cutting with healthy tissue. Be sure the “parent” plant is well hydrated. The cells in the stem cutting need moisture in order to start knitting together to create a root system. BUT, do not allow the cutting to remain too wet or debilitating fungi will develop.
Second, select a clean, sharp cutting tool. You do not want to damage the parent plant or the stem of the cutting by using a dull blade. Using either rubbing alcohol or a 10% bleach solution to clean the blade before making any stem cuts will guard against pathogen transfer which could adversely affect the health of your cuttings.
Third, stem cuttings should be 4 – 6 inches (10 – 15 cm) long…ideally. Make sure to cut the stem right below where the leaf, or leaves, are attached. This is called the leaf node and roots grow easiest from this part of the stem. Do not leave a length of stem below this point as it will rot and the stem cutting will die.
Fourth, remove any flowers and fruits which are on the stem cutting. They will rob the much-needed food energy from developing roots.
Fifth, remove the lower leaves, leaving just two or three at the top of the stem cutting. No leaves should be buried below the surface of the growing medium. If the stem cutting is from a large-leaf plant and therefore top heavy, you can cut the leaf in half horizontally to get rid of some weight. Just be sure there is enough leaf left to ensure photosynthesis is not impacted. The stem cutting needs the sugars this process produces.
Sixth, if you are not ready to plant your stem cutting just yet, place it in a cup of water to keep hydrated while you are organizing your planting pot.
Rooting medium for starting cuttings
Best to use a soilless mix such as perlite, vermiculite, sand, or a combination of a soilless seed starting medium with perlite or vermiculite or sand mixed in. I generally use seed starting soilless mix with a generous addition of perlite mixed in to improve drainage. DO NOT use soil from your garden beds or compost as they contain many soil organisms such as fungi and other pathogens which can be deadly to stem cuttings…and young seedlings too for that matter.
Fill a suitable pot or container with your planting medium of choice. I usually take four to six cuttings of each plant species I want to propagate, depending on their size and how much space I have for the number of pots I will be making up. As in germinating seeds for new plants, you will not have 100% success with your stem cuttings. Some plant species are tougher to propagate than others. My success rate typically falls around 50% on average.
All plants contain a natural rooting hormone called auxin which not only stimulates growth but also signals a bud when not to grow. This helps stem cuttings develop new roots from the cut leaf node.
However, there are products on the market that will help the process. Synthetic auxins have been on the market since the 1930’s. The ones available to home gardeners contain chemicals such as indolebutyric acid (IBA) in alcohol or a-naphthaleneacetic acid (NAA) in talc. The dry hormone preparations usually contain fungicides to help prevent powdery mildew on the cuttings. These are not allowed under certified organic criteria.
We use the NAA rooting hormone and there are three types…each specifically manufactured to use with one of the three types of stem cuttings:
- #1 is used with softwood stem cuttings.
- #2 is used with semi-hardwood stem cuttings.
- #3 is used with hardwood stem cuttings.
Before dipping your cutting, be sure the bottom of the stem is wet…which it should be, if your cuttings have been sitting in a cup of water.
Never, ever dip the end of the cutting straight into the rooting hormone container. The moisture on the cutting will degrade the rest of the hormone. Always pour a little of the powder into a small dish or cup and re-cap the hormone container right away. Also…dispose of any unused portion of the hormone in your dish. Never put it back into the original container.
Note: Make sure the rooting hormone is covering ½ – 1 inch (1.25 – 2.5 cm) on the bottom of the cutting.
Planting the cutting
When your cutting has been dipped in rooting hormone…if you are using it…and ready for planting, make a hole in your growing medium. (Be sure your medium has been moistened with a little water. You want it damp but not soaking wet.) A pencil works great for this, or some such similar tool, but be sure the hole is a little bigger than the diameter of your cutting so the rooting hormone is not rubbed off. Gently press the medium around the cutting to provide good contact between the stem and the rooting medium.
Now…this is where it gets tricky. Many growers tell you to cover your pot with a plastic bag, or cover your tray with a plastic tray cover. This is quite true, as you want your cuttings to stay hydrated.
But this only works IF your cuttings are in a totally sterilized environment. Any pathogens adhering anywhere in the growing medium you used, on the pot, or on the utensils you used in your propagating process will flourish in the humid environment manufactured within the bag or tray cover will breed decay.
You can minimize the odds of disaster by removing the bag or tray cover for a few hours each day and allow some breeze to gently brush the cuttings.
My method: I prefer to just leave the cover off and monitor the soil moisture on a daily, or thrice weekly schedule. As long as the growing medium remains slightly damp…not saturated!…then chances your cuttings remain adequately hydrated are decently good.