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.
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.
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.
Give cuttings bright light but not sun. Keep soil moist but not wet. The cuttings should root within three weeks. Admit air gradually to wean the cuttings from their humid environment, then pot singly before outdoor planting.
LIGHT AS IMPORTANT ENVIRONMENTAL FACTOR FOR ROOTS
One of main roles of light in plant's life is to provide energy for photosynthesis and for the regulation of plant development at different stages such as seed germination, vegetative growth, tropisms and flowering.
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.
Propagation requires the proper balance between light, temperature, and humidity. Using supplemental lighting for plugs during low light intensity times of the year will see an increase in photosynthesis, faster flowering, increased root structure, stronger and sturdier plants and faster crop cycles.
Clip off the leaves on the lower half of the shoot so you have a bare stem to insert into your potting mix. Then, if you want, dip the end of your stem in rooting hormone. This generally helps cuttings root more quickly.
Thanks to their bottom heat and high humidity, heated propagators can also be instrumental in helping cuttings to take root. Whatever you're growing, a heated propagator will protect germinating plants from sudden cold snaps like we're having at the moment.
The reason cuttings rot is that over time, the oxygen level of the water drops unless it's moving or oxygen is added. Not only do plants need oxygen in order to grow roots (and, indeed everything else), but the bacteria that cause rotting thrive in low-oxygen environments.
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.
Early morning is the best time to take cuttings, because the plant is fully turgid. It is important to keep the cuttings cool and moist until they are stuck.
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Cuttings need water for hydration, but also enough oxygen for roots to respire and grow. Using a substrate with adequate air porosity, and using the 1 to 5 moisture scale can help to prevent overwatering that leads to slow rooting and increased risk of disease.
Herbaceous cuttings can be taken throughout the growing season (spring to late fall), while softwood cuttings should be taken in spring or early summer. Cuttings can be taken as long as the parent plant is healthy and in active growth.
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.
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.
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.
Too much or too frequent application of mist / fog keeps the growing medium saturated, excess water will flow from the bottom of the trays and rooting will be delayed. Applying mist / fog too infrequently will increase transpiration from the leaves and cuttings will lose turgidity and could die from drying out.
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.
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.