Adding supplemental lighting to cutting (clone) production can greatly increase the chances of a successful crop, along with faster root emergence and crop times. If the Daily Light Integral (DLI) is too low during propagation, leaves will be unable to get enough light for photosynthesis and rooting can be delayed.
Light provides the energy for callus formation and the subsequent generation of adventitious roots. At the same time, light increases plant temperature and accelerates the drying of leaves, which can quickly dehydrate cuttings. (Under LEDs, this would be less of an issue.)
We recommend a photoperiod of 12-13 hours for the propagation of most annuals, especially for long-day plants such as petunia. Light Intensity. Desirable levels of light vary, depending primarily on the stage of root development. The following is a guideline for managing light intensity for high-light crops.
The best light cycle for rooting cuttings is generally 18 hours of light and 6 hours of darkness. Do not supply cuttings with 24 hours of light without any dark periods because this has shown to slow the rooting process down as plants root best with a sufficient dark period each day.
Roots grow in the dark soil to anchor the plant and to absorb mineral nutrients and water. It has been reported that light can penetrate less than several millimeters due to the rather high absorbance of soil (Woolley and Stoller, 1978).
Cuttings will root more quickly and reliably in warm rooting mix. Keep your cuttings between 65°F and 75°F, avoiding excessive heat. If your area is too cold, consider a heating mat or cable especially designed for this purpose.
Providing too much moisture during propagation can result in rot and cutting loss. A practice often observed during propagation of unrooted cuttings is frequent, heavy misting, which provides too much moisture and should be avoided.
Several cuttings may be placed together in one container. Be sure to add fresh water as needed until the cuttings are fully rooted. Rooting will generally occur in 3-4 weeks but some plants will take longer. When the roots are 1-2 inches long or longer the cutting is ready to be potted up.
The problem is if the cutting is too long the plant is more likely to wilt and stress. If the cutting is wilting it's far more likely to fail and not generate roots. Smaller cuttings will lead to better success rates and overall better outcomes for you and your cuttings.
Place your stem cutting in your vessel with enough water to cover the node. The water level will drop due to evaporation, so you should add water every 3-5 days as needed. You can watch the roots develop if you have chosen a clear vessel for your cutting.
Cover the Pot With Plastic
Place the container with the cutting into a plastic bag. The bag will keep the humidity high and hold in heat. Do not seal the bag completely because some airflow is necessary to prevent fungal rot.
All cuttings need to go directly to an environment with 100% humidity after being cut. If the cuttings dry out, they will not do well. Keep them dark, cool and moist. If you are working in large areas, use wet cheesecloth or burlap to wrap the cuttings as you go along.
Warm growing medium temperatures accelerate cell division which leads to faster callusing, root initial development and subsequent root growth. It also speeds up the dry-down rate of the growing medium, which also helps encourage better rooting. The best way to warm the growing medium is through bottom heat.
Roots themselves are also light-sensitive, so despite the fact that they will absolutely grow in a clear container in sunlight, you will find more success and faster propagation as well as avoiding algae growth in a dark glass or opaque container.
Technically, you can transfer your cuttings to soil at any time. In fact, you can actually propagate directly into soil, however, it's much harder to do within your home. When you propagate in soil, you have to keep a good balance of soil moisture, air flow, and humidity.
Some plants will root in water, but cuttings will develop a better root system when rooted in a soil-less potting mix. Sand or perlite can also be used, especially for cuttings that need good drainage and may rot if kept too wet.
The basic principle behind applying mist to vegetative cuttings is simple. Without roots, cuttings cannot adequately replace the water lost to the environment due to evaporation and transpiration mainly. To aid them along the beginning of their life journey we must replace this water loss with water applications.
Try to wait until at least 50% of the cuttings have good rooting before potting them up; however, for some hard-to-root species, you may be lucky with only 10% to 20% success.
Add your cutting, and then mist the surface thoroughly daily (trying not to get the cutting). Twice a day if it's hot or dry. By 'mist' I mean properly wet the surface of the soil. Every week or so, stick your finger in the soil further down, and water it 'properly' if it's dry.
Ideally, the temperature of the medium should be maintained slightly higher (5°F-8°F) than the air so that callus and root growth occur faster than shoot growth. To accomplish this, bottom heat- ing is required. Desirable propaga- tion temperatures are 73°F-77°F for the medium and 68°F-73°F for the air.
Add fresh, tepid water when needed. You can replace the water every few days, or simply top off the vessel with fresh water when it's looking low—as long as there is no murkiness or fungi growing. If the water is murky, we recommend replacing it for the health of the growing root system.