The purpose of using heat specifically in the root zone of cuttings is to induce dormancy in the upper vegetative part and to encourage root growth at the base. The temperature difference between soil and air gives the plant a boost for root formation rather than stimulating new leaf growth.
Cuttings will root more quickly and reliably in warm rooting mix. Keep your cuttings between 65°F and 75°F, avoiding excessive heat.
This has been answered by others and I agree with them. Basically, take the cutting, put it into a media, either water or soil, make sure the media is free from fungi/pest. To increase/promote root growth, make a slice to expose more of the plant's part to the media.
Bottom heating of the pot also helps to stimulate root formation. Portable heat mat can be purchased through avenues such as gardening magazines. A hot water heater can also be a source of bottom heating ie put your pots on top of a water heater.
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.
They'll root faster with plenty of sunlight, but avoid setting them in direct sun. Temperature is also important, the warmer the better to speed things up. For cuttings that are more valuable or difficult, adding a little aquarium pump to oxygenate the water will help a lot. Roots need the extra oxygen to grow well.
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. Therefore it is vital that the plants you take your cuttings from are healthy, pest-free and growing strongly.
Honey & Cinnamon Rooting Hormone
Dip the end of a cutting into honey water made with 2 cups of water and 1 tablespoon of honey. Then dip the same cutting into cinnamon powder. I have a gardener friend who swears by this treatment for challenging cuttings that often succumb to fungal problems.
Sand or perlite can also be used, especially for cuttings that need good drainage and may rot if kept too wet. Many easy-to-root plants will not require the use of a rooting hormone but doing so will assure faster rooting.
The rooting medium should be sterile, low in fertility, and well-drained to provide sufficient aeration. It should also retain enough moisture so that watering does not have to be done too frequently.
For plant roots to grow faster, it requires nutrients, sufficient water, well-aerated soil, enough light, the right range of temperature and proper amendments. Nitrogen, phosphorus and potassium are the three essential nutrients that a plant requires for its growth.
The two main nutrients that support excellent root growth in plants are phosphorous and potassium. These two ingredients are extremely helpful in any fertiliser mix that needs to encourage a thick, healthy collection of brand-new roots, or to strengthen and stimulate existing systems.
Plant the Cutting in the Soil
Carefully plant the cutting in the hole you made in the potting mix, and gently tamp the soil around it. You can fit several cuttings into one container, but space them so the leaves do not touch one another.
Remove the bottom leaves and buds of the shoot so the plant devotes its energy to forming roots rather than growing leaves or flowers. Sprinkle rooting hormone powder on a saucer. Dip the cutting in the powder, which will encourage root growth once it's planted.
Another way to reduce water loss is to keep the cuttings in a humid atmosphere – place a clear plastic bag over individual pots or use a propagator with a lid.
Inadequate Moisture: Cuttings need to be kept moist, but not waterlogged. Overwatering can lead to rot, while under-watering can cause the cutting to dry out and die. Use a spray bottle to mist the cuttings regularly with fresh clean and ensure the soil is consistently moist but well-drained.
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.
A root stimulator sounds like a fertilizer, but it's not quite the same. It contains a hormone called auxin that young plants produce when forming their root systems. Root stimulators typically have a host of other vitamins and nutrients that encourage the growth of roots, too.
5. Pairing your propagations with faster rooting plants such as spider plants, pothos, swedish ivy, tradescantia, or if you can find a willow branch, add that to the water vessel too! It can really help speed up root development!
Using apple cider vinegar as a rooting hormone is a safe and natural way to weaken the outer coating of seeds, making for faster germination.
Embarking on your quest to propagate plants, you might wonder, "What can I use instead of rooting hormone?" Cinnamon emerges as a stellar candidate due to its natural antifungal properties. These properties help safeguard your delicate cuttings against common fungal threats that often compromise root development.
Add a Pothos! I'd heard of using willow as a natural rooting hormone (no idea where to source that however), but didn't know Pothos has this 'super power' too! Just pop a Pothos cutting in with the water with your slow-to-grow cuttings and it helps speed up root development.
Soil and air temperature affect the success of rooting from dormant cuttings, as root metabolism, that is temperature-driven, governs root growth and uptake (WIERSUM, 1980).
Before you take a plant cutting, fill your pots with compost and water them so that they are ready for the cuttings. Take cuttings early in the day when the plant's stems are full of water. Place cuttings in a plastic bag to stop them drying out and use them as soon as possible.
Filtered water: If you don't have access to clean or distilled water, you can use filtered water for houseplant propagation. Filtered water can remove some of the impurities that are present in tap water, such as chlorine and minerals.