I have taken cuttings from my Coleus plants and rooted them in water. They now have about 2 inches of fine roots growing. I’m planning to overwinter them. Should I pot them up in potting soil now?
According to Coleus: Rainbow Foliage for Containers and Gardens by Ray Rogers (Timber Press, 2008), growing Coleus from cuttings (rooting them, as you did, in water) is a fine way to propagate more plants. The cuttings will survive for weeks or even months in nothing but water, and with soluble fertilizer, this time could even be extended.
However, since you want plants which may eventually live somewhere other than the windowsill or counter, Rogers recommends removing the cuttings from the water when roots are an inch or two long, and planting them in growing medium. This is because roots which are produced in water are less sturdy, so making a transition to growing medium helps the plant develop. (Long water roots are easily damaged if pressed too hard when potting them up.) As for the potting medium, even garden soil can be used if it is not heavy clay and does not dry out. Since you are going to keep your plants indoors over winter, you may want to use purchased potting mix which has an open structure (drains well but will not dry out too fast). The mix might include bark, coir, perlite, pumice, or other ingredients. The author has a preference for vermiculite, but be careful to wear a dust mask when handling any fine materials; you definitely don’t want to get particles in your lungs.
Once you’ve potted the cuttings, keep the medium moist but never soggy, and keep them humid (using a mister, for example). Cuttings need bright light but not direct sun, and should be kept at about 70 degrees. If room temperature drops below 50, you may want to set the pots on a heating mat. You don’t need to add fertilizer while the cuttings are getting established. You can move the cuttings into larger pots once they’ve developed a strong root system (at least a week).
Other tidbits of information that may be useful:
- Cuttings can be taken from any piece of stem on the parent plant, but it’s best to choose stems which are neither the youngest nor the oldest growth.
- Cuttings taken from the sunnier side of the plant have firmer tissue and may root more strongly than cuttings from the shadier side, but they will also need consistent humidity and protection from intense sun while rooting.
- Cuttings will look like the parent plant if the parent plant is a genetically stable cultivar, but some cultivars (especially with pale pink in the center of their leaves) are more prone to reverting or sporting.
- Once night temperatures outdoors are above 60 degrees, it should be safe to move your plants outdoors (but it’s always a good idea to harden them off gradually beforehand).