Especially with cuttings, it's often desirable to have a cooler (5 to 10° F) air temperature than root tempera- ture, which allows the roots to grow more quickly than the shoots. Erik Runkle is associate professor and floriculture extension specialist in Michigan State University's department of horticulture.
To improve success with rooting of cuttings it is best to maintain media temperatures between 68-77°F; even cold tolerant crops such as pansy, dianthus, osteospermum, petunia, etc. prefer these media temperatures for rooting.
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.
Temperature has a strong effect on propagation because it changes the degree of longitudinal (axial) current flow. The longitudinal current is determined by the difference in potential between the region where the impulse is at its peak and the region ahead (normally resting).
Cuttings from many annual plants will keep over winter, sprout roots, and be ready for planting in spring. You may place them in pots or cups without drainage filled with moist perlite or vermiculite. Locate them at first in bright light, away from the sun. Move later to an area where they receive morning sun.
It will slow transpiration while the necessary components are used at the root sites to build a new root structure. Keep the atmosphere around the cutting warm (not hot), keep the humidity relatively high (>90%), and keep the root zone temperature warm (at about 25°C).
Environmental conditions: Environmental conditions like availability of water, light, temperature and rooting media may also affect the root initiation process in cuttings.
Effect of environmental factors: Among the external factors affecting the rooting of cuttings, moisture, temperature and light play important roles.
According to Richa, overwatering is the most common failure. 'When propagating cuttings, it's important to ensure the soil is moist but not waterlogged,' she says. 'Overwatering can easily lead to root rot. To avoid this, wait until the top inch of soil is dry before watering your cuttings.
Plant cuttings mistakes can range from using dirty tools to potting up your cuttings in the incorrect potting soil. Too much harsh sun, too much or not enough water, and using offcuts from plants that are sickly or flowering can also put your cuttings at risk.
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.
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.
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.
Relative Humidity and Airflow Management
It is recommended maintaining the relative humidity in a propagation house at a minimum of 85 percent. This can be done with mist or fog systems.
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.
Auxins stimulate root formation on the stem cuttings, e.g., IBA, IBA-alanine, NAA. NAA is synthetic auxin while IBA is considered as both natural and synthetic.
Phosphorus (P) and potassium (K) are the two main nutrients that stimulate root growth. Organic fertilisers often display the relative quantities of each, as well as nitrogen (N), in the form of the NPK ratio. In particular, phosphorus allows new root systems to spread through the soil or another growing medium.
These commercially available products typically contain indole-3-butyric acid (IBA), a chemical form of the plant hormone auxin. Naphthalene acetic acid (NAA) is a synthetic rooting hormone that also helps prevent rotting. Both of these chemicals help stimulate root growth.
From stick to root development (Stages 1-3), propagators sometimes use too little water or moisture, but most often provide too much water, which leads to leaching and waterlogged propagation substrates (Fig. 1), uneven rooting and loss of cuttings due to rot (Fig. 2) or botrytis.
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.