I have had only very limited success in years past propagating plants from cuttings. It is something I always wanted to do, but was the one aspect of gardening I failed at, time and again.
In Michigan I really did not have a good setup. Very few windows with nice light, and cats all over the house. Before moving to Tennessee I took a lot of cuttings of bushes I would want for my new property and put them in trays and put them outside in the shade with humidity domes and they all rotted eventually.
Here I have tried it a few times. Rooting in water then transplanting, rooting in soil with bag or something over it as a humidity dome, rooting in a tray again with a humidity dome, rooting in a tray with rock wool plugs and a vented dome. I had a lot of failures. Some things worked in water, sweet potatoes, etc. But most did not. The rock wool plugs and dome worked okay, until everything inside rotted. Some things had rooted, but they rotted anyways. I had the dome on, and sealed, for a couple weeks, opened it to check on things, looked good, so I vented it and put it back on, and in two days mold on everything.
I feel like a rooting medium really is best, not just water. Roots are lazy, if they get everything they need right outside the front door they aren’t going to walk around the block and look for things. So for many plants rooting in water will not work because the water and any nutrients are too readily available. This is also why you should water containers deeply and let them dry out between waterings. Otherwise (and again, this is species specific, there are exceptions) plants will only put roots in the top part of the soil because they’re able to get everything they need from there without growing deeper. This is also why bottoms up watering systems work so well.
But for me, getting the humidity just right so that the plant survives long enough to put out roots while not rotting has been the major challenge… until now.
I’m blessed to have a greenhouse, a real legit one, climate controlled, automatic venting, etc. It is humid and super damp inside, but there is good airflow because of fans. So what I finally figured out is if I just plant cuttings in potting mix (sand might be better, but potting mix is working fine) and do not use a dome, they do fine, they get sufficient humidity just from being in there. My cutting success rate now seems to be close to 80%, which is way better than 0%.
I’ve been doing some hardy hibiscus and buddleia and hydrangeas and some other things such as shrubs for hedges and am having pretty good success. I go in once a day, most days, and mist the cuttings with a spray bottle and they have been tied into my automatic watering system and things are going well. I have a giant property and this will allow me to get the volume of plants I need to landscape it all without breaking the bank.
One strategy I’ve adopted is to place multiple cuttings in each little pot. This way if I do have failures odds are I’ll still end up with something growing in that pot – and if all 3 or 4 succeed I can always thin out the weakest.