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.
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.
It's also worth reducing water loss by removing the lowest pairs of leaves from each cutting, and snipping the leaves of larger-leaved plants in half. 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.
Lack of oxygen
Plants absorb oxygen as well as other nutrients through their roots. As your plant sits in water, it releases carbon dioxide and absorbs all of the oxygen. If you don't change the water, it can run out of oxygen. This is the #1 cause of water propagation stem rot & root rot.
Using sickly plants or flowering shoots
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.
Cut off any diseased roots using a sterile cutting tool like a knife or scissors. You want to make sure that you're cutting off the roots that are black and mushy. After you've cut off any dead roots, we recommend soaking them in an 80:20 solution of water to hydrogen peroxide.
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.
Cuttings use energy to form new roots. If the cutting has leaves, most of the energy comes from photosynthesis. Expose these cuttings to bright light, but not direct sunlight, during the rooting period. If you use hardwood cuttings that have no leaves, the energy will come from reserves stored in the woody stem.
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.
In most situations, mist is required during the first night or two after sticking because the cuttings are “leaky” and have difficulty taking up water as rapidly as they're losing it through transpiration. With each passing day in propagation, the cutting regains its ability to regulate water loss.
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.
It's important that your water propagated plants receive some light, but bright indirect light with no direct sun is important. They are growing new root systems and are fragile.
Using Water
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.
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 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.
Change the Water Regularly or Use Activated Charcoal
To prevent bacterial growth and maintain a healthy environment for rooting, remember to change the water in the container every few days. Alternatively, you can add a small amount of activated charcoal to the water, which helps keep it bacteria-free.
Hydrogen peroxide can help to control fungal growth and fungal infection, such as root rot, by preventing the growth of fungi. It can also help kill fungus and bacteria on plant roots.
Best way to tell if it has put down roots is to note whether it has died. Sound obvious but sometimes a green cutting can last for a long time without roots, but eventually it will dry out and turn brown. If you see any new buds or growth, that's an indication that something is going on down below.
Another product that'll help prevent the spread of root rot is non-flavoured cinnamon. After having removed the dead roots, sprinkle a thin layer onto the healthy tissue before placing into a bed of new compost.