Place the tray of cuttings into a plastic bag. This mini-greenhouse will keep the cuttings moist until roots develop. Monitor cuttings weekly for root development. These hydrangeas developed roots in three weeks. Pot up rooted cuttings into quart-size containers, water them well, and transfer them to a sunny spot .
Some cuttings root faster than others.
I've found that the best way to check for root development is with my eyes. After four to five weeks, I can check the bottom of each tray for small white roots that may be poking out of the drainage holes. If none are visible, another way to check for root development is by gently pulling on a cutting. If it shows some resistance, then it's a good bet that roots have developed. If it pulls out of the tray easily, I inspect the stem for very fine root hairs.