A Smarter Way to Select, Store and Process Stem Cuttings
Unlike cloning herbaceous plants, woody cuttings require slightly different consideration. Here’s how to properly select, store and process stem cuttings (as opposed to leaf or root cutting), using rooting hormones and creating the ideal rooting environment.
Selecting the right cuttings
Making the proper selection of stem cuttings is an integral first step for reaching success. Seasonality creates differences in physiology within the plant; thus, there are three classifications of cuttings: softwood (spring), semi-hardwood (summer) and hardwood (fall and winter). Each type of cutting will require slightly different procedures.
Softwoods derive their name because they are the soft, new and non-woody growth that emerges in spring and sometimes summer. Their rooting potential is high, but they will easily wilt and rot under sub-optimal conditions. Semi-hardwood cuttings occur during a transitional period when softwood starts to form a woody protective layer.
In non-tropical areas, this is a protective measure against cold temperatures during the winter. Semi-hardwood cuttings are not as delicate as softwood cuttings, but they will wilt if exposed to low humidity. Lastly, hardwood cuttings are often taken from dormant plants (those without leaves) during the fall and winter. These cuttings are the least finicky in terms of care and can be bundled together, placed in a refrigerator and stuck later in the spring.
Another important consideration is the age of the plant. In general, the age of the plant greatly influences the rooting potential of the cutting. Juvenile plants produce cuttings that root far better than older plants. While the exact reason is unknown, some scientists attribute this decrease in rooting potential to an increase in root-inhibiting compounds. Personal experience has shown that rooting from mature plants is still obtainable, albeit at significantly reduced percentages; nonetheless, it’s best to stick to younger plants when possible.
The position from which the cuttings are taken can also impact rooting potential. Distal (closer to the end of a branch) and proximal (closer to where the branch attaches to the trunk) can influence rooting percentages depending on the plant of interest. That is to say, for some plants, rooting potential will be higher when taken from the very end of the branch, whereas the opposite is true with others.
Lastly, before the cuts are made, make sure the plant is not under water stress and that growth is neither very vigorous (high in nitrogen and low in carbon) or very stunted (often an indicator that the plant is older or not growing in favorable conditions). All of these factors will reduce rooting potential.
Now we are ready to make the cut. The ideal cutting size depends upon the type (softwood, semi-hardwood or hardwood). Sizes range from 3 in. for softwood to 12 in. or more for hardwood cuttings. In general, 3 to 8 in. cuttings are ideal for all types. If the cuttings are softwood, pay close attention to the terminal growth. If it is quite soft and easily bends, remove it as rotting will usually occur.
While length is an important measurement, pay close attention to the nodes (place were leaves attach to the stem) per cuttings. Each cutting should have at least two nodes (three is preferable). The cut should be made directly above a node on the “parent” plant.
Storage conditions and processing for stem cuttings
Now that you have made the cut(s), proper processing and sticking should occur. However, if this is not possible and you are working with softwood or semi-hardwood cuttings then preventing water loss is integral. This can be accomplished by immediately placing the cuttings in a plastic bag, which is then sealed.
It is also preferable to mist the cuttings prior to sealing, but if you do not have access to water simply use a sealable bag. If outside temperatures are hot, a cooler is a great place to put your sealed bags. Keep in mind that water stress in softwood or semi-hardwood cuttings can occur quickly (seconds to minutes).
The next step in processing is removal of leaves. While some authors instruct removal of all but the top set of leaves in softwood and semi-hardwood cuttings, some disagree. Leaves are the carbohydrate manufacturing center for the plant; therefore, these leaves provide the necessary energy needed for root development. While removing leaves reduces the surface area for water loss, pruning the bottom leaves that touch the rooting substrate is sufficient.
Also, depending on the plant, wounding the cuttings might be needed to induce root formation. This is often necessary with hard to root plants like rhododendron, magnolia and pinus. To wound, use a clean sharp knife or pruners to scrap away the outer layer (1 to 2 in.) to expose the inner green layer. Make sure you do not go too deep and cut into the pith, which is often white.
Generally, cloning woody ornamentals is enhanced through the use of rooting hormones. Natural rooting hormones are derived from plant chemicals known as auxins, and manufactures utilize the synthetic-derived auxins indole-3-butyric acid (IBA) or alpha-naphthaleneacetic acid (NAA).
Auxin promotes root initiation by programming cells to develop into new root cells. The type of cutting dictates the appropriate amount of this chemical to use. In general, I have had good success using 500 to 1,000 ppm on softwood cuttings, 1,000 to 3,000 ppm on semi-hardwood cuttings and 4,000 to 10,000 ppm for dormant hardwood cuttings.
Beginners to vegetative propagationshould try a rooting hormone that is mixed in talc powder. This will be relatively inexpensive, easy to use and, in general, will not burn the cuttings. The main drawbacks to this are that the concentration of IBA is fixed (usually 0.1% or 1,000 ppm) and the IBA in talc is relatively insoluble, so absorption might be sub-optimal.
Also, the talc powder easily comes off (especially when sticking into the substrate) and is therefore ineffective. Another type of auxin delivery is gel based. This gel adheres to the cutting better than talc, but is usually more expensive and has the added danger of burning certain sensitive softwood cuttings.
Also, like talc, the concentration of auxin is fixed in gel-based solutions. Lastly, another popular auxin carrier is a liquid-based solution (often a solvent like isopropyl or ethyl alcohol). The stock solution is quite high (10,000 ppm) and can easily be diluted with water to acquire the desired concentration.
This method is a quick dip where the auxin is highly soluble and readily absorbed; however, the price is usually much higher and the solvent readily burns cuttings if the optimal concentration is exceeded. I have experienced the greatest success using rooting hormones that are solvent based, but would not recommend it for those trying root hormones for the first time.
Ideal conditions of optimal rooting of stem cuttings
Since the cuttings have been severed from the parent plant and do not possess a root system, their ability to absorb water and nutrients is drastically reduced. Cuttings will lose water from both the leaves and the cut end until it heals over; thus, maintaining high humidity is critical. Without humidity, the cuttings will quickly lose turgor pressure and wilt. On a commercial scale, misting systems allow high humidity coupled with good air circulation, which significantly reduces fungal rotting.
However, most hobby growers do not have the aforementioned misting systems. In this case, hand misting with a sprayer often times is less successful than using some sort of dome. Depending on your growing environment, water droplets from misting can quickly evaporate away, creating an environment that favors pulling water out from the leaves. For better results, take your cuttings, mist the leaves (top and bottom) and place them in a plastic dome top or baggy.
Just make sure that the environment is sealed and that no leaves are touching the bag or dome, as this will lead to rotting. Check on the cuttings every day or so to make sure the substrate is moist and not waterlogged, that the leaves are healthy—remove yellow or brown leaves—and to the check for root formation.
For traditional soilless mixes, such as peat moss, coco coir, perlite and vermiculite, the grower is confined to check on root formation by gently tugging on the cutting and feeling for resistance. With cellular-matrix substrates, you can remove the whole plug to see if root formation is penetrating out without risking damaging the roots.
Patented plants and illegal propagation
While some of you are coming around to the idea that cuttings could be quite lucrative, be forewarned that the plants you buy from a nursery have been developed by growers and are either patented or patent-pending. That means you cannot reproduce these plants for profit without notification and subsequent payment of royalties for each cutting. However, you can reproduce plants for your own use (or for a neighbor, if you are that kind!) so long as you do not intend to sell them for profit.