As a rule, take up cuttings when roots are half an inch long. You can check by gently lifting one cutting and gently putting it back if roots are still too small. Try not to let cuttings remain overlong before transplanting to more spacious quarters and richer soil. It takes only a little experience to get a feeling for the right time. For most transplants the equal-thirds mixture of garden soil, leafmold, and sand is good, with a little extra leafmold for those plants that are developing fine root systems, as African-violets and begonias.
Make the first transfer of rooted cuttings to 2 1/2- or 3-inch pots nothing smaller because the soil will dry out so quickly you will never have the watering can or hose out of your hand. However, it does help to plunge well-watered small pots into a bench section of sand, vermic-ulite, or perlite which can then be kept fairly moist, and the moisture will penetrate the walls or clay pots. Still, you must check frequently' for too much moisture rots new roots by keeping soil so wet that air cannot enter.
If your clay pots are new, soak them in water for several hours before using because dry clay draws moisture from the soil. I soak old pots overnight in a strong Lysol solution to disinfect them and then rinse well in clean water. If algae and accumulated salts remain, I scrub with a wire brush till pots are clean sometimes a laborious business.
When many seedlings or cuttings are to be transplanted, an assembly line speeds the work. Set pots in rows on your potting bench. Place a bit of broken pot, a stone, or a little unmilled sphagnum moss or os-munda fiber over the drainage hole in each one to prevent soil from washing through. Scatter over this a small amount of horticultural charcoal to help keep soil sweet. Then fill pots with the planting medium to within a quarter- to half-inch of the top, depending on pot size. Insert a plant in each and water moderately. Once plants are established and growing, start a regular schedule of feeding.