The cold air will keep the buds from opening and forming leaves, and the heater will keep the mix warm enough for roots to form (65 to 75°F). It is acceptable for the air temperature to go below freezing as long as the heater can keep the rooting mix between 65°F and 75°F.
Media is usually kept at 72-77° F while air temperature is maintained at 68-73° F. If bottom heat is not used, air temperature should be maintained between 77 and 80° F. Maintaining air temperatures lower than medium temperatures retards shoot growth while promoting root development. Excessive heat can damage cuttings.
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.
In general, the rooting medium should be sterile, low in fertility, drain well enough to provide oxygen, and retain enough moisture to prevent water stress.
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.
Auxin, a naturally occurring plant hormone, stimulates root formation. Several synthetic forms of auxin are sold as “rooting hormone.” Though some plants will root readily without treatment, application of rooting hormone to the base of the cutting will often improve your chance for success.
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.
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.)
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.
Cuttings are very delicate and vulnerable so pests, disease, the wrong growing conditions, too much water or too little water can all cause them to fail.
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.
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.
The sooner you can get your cuttings into a more normal environment with air flow and no dome, the better off they'll be. After about a week, remove the dome and monitor your cuttings to see if they begin to wilt. If they do, they're not ready to go dome-less, so try again in 1-2 days.
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.
Most plants will not root well in full sun, so place the cuttings in a location where they will receive a 50/50 ratio of shade to dappled sunlight. For most plants, cuttings thrive on warmth and humidity, and the growing medium should be kept evenly moist but not drenched while roots develop.
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.
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 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.
Controversially, I'm gonna suggest you don't water them very often. I would start with very evenly moist airy soil – water in sans cutting, and mix it round so it's not saturated at the bottom. 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.
Phosphorus potassium &Nitrogen are the essential nutrients to support root growth for plants. They encourage plants to put down a dense collection of new roots and strengthen existing roots as they develop. Phosphorus helps establish healthy root systems at the beginning of growth.
Roots need air in order to grow. You should try and change the water with fresh tap water every 2-3 days or so for best results because oxygen in the water will be depleted.
Roots are dynamic and their growth is strongly affected by the environmental conditions found in the root zone. To survive and grow, they need Air (gas exchange), Water, Non-limiting Temperature, Carbohydrates, Minerals, Space, Low Soil Density, Microbial Associations and Non-toxic soil chemistry.