Updated: Dec 6, 2020
When I was starting out with plants, the term "propagation" seemed overwhelming and complex to me. I was a previous here-and-there plant owner, who would try my hand at keeping any potted plant I was gifted alive, until it died, I sadly laid it to rest, and waited for the next potted plant to enter my life.
Propagation is simply the breeding of specimens of a plant or animal by natural processes from the parent stock. Essentially, it is the controlled perpetuation of plants. Some people simply use it to increase number of plants, while others control to preserve essential characteristics of the plant (like my Monstera Deliciosa node/leaf I bought for $10 that has given off an albo baby. I plan to chop and keep propping to initiate more albo shades!) And, it's much easier than you might think!
Firstly, know that propagation is a learning process, and you may have some casualties! That is quite alright. :) Pay attention to what works and doesn't work for you. As I heard it described in the Bloom & Grow Radio podcast, water propagation is simply a race to root before it rots! When you have casualties, pay attention to the conditions that allowed for them to rot before they could root!
Of course, there are multiple media through which you can propagate plants: soil, semi-hydroponics media such as LECA (which will be further explored on my Youtube Channel!), and water propagation.
Water propagation is best for Aroid plants. These are from the family Arcaceae and include common houseplants like agalonemas, monstera, philodendrons, pothos, and ZZ plants. The science behind this group of plants propagating in well in water has to do with evolution, not surprisingly! This group of plants has spread all over the globe, except in Antarctica, and they are found in their natural habitats growing across the forest floor. These are oftentimes referred to as "low light tolerant plants," because they have adapted to surviving in many conditions, including being on the bottom of heavily-forested floors where not much sun may poke through. (Side note: just because a plant is low-light tolerant does not mean it prefers low light. Often, these plants are kept from their full thriving potential by taking advantage of their adaptation and hiding them in the shade 24/7! Aroids love sunshine too! They have adapted to survive in low-light, but even in the understory, sun shines through.)
The Araceae family boasts herbaceous perennial plants, often with milky, or clear acrid sap. The ancestors of aroids were lowland swamp-dwelling plants that experienced floodings. Through what we may call mass-scale propagation to select for specific traits, the plants that survived floods became the ancestors of all aroids we know and love today. Evolution has allowed for the transmission of the ability to root in water, through the aroid family. This is evident in the observable foliage and roots of aroids: typically, the leaves and roots are waxy. Thick roots are an adaptation that help resist absorbing too much water, helping to protect the plant from hypotonicity and root rot.
Now that we know the history of plants that easily water propagate, lets talk about the media itself. Water on its own does not supply nutrients to the plant like some organic soils would. Therefore, while some plants are happy to live in water indefinitely, most will eventually need to be transplanted into soil or LECA, and fertilized or fed nutrient water after the roots have grown long enough. I usually recommend waiting until the roots are over an inch long before transplanting. (I always use Superthrive when transitioning into a new media such as LECA or soil- helps with reducing shock.)
So, you're ready to propagate. Go grab the plant you've had your eye on multiplying, a pair of sterilized pruning shears (or kitchen scissors in my case), and any glass vessel filled with room temperature, preferably filtered water.
Take a mature vine and search below the leaf /on the stem for a tiny brown root node. These will often be a knuckle-like protrusion on the stem, with tiny brown roots starting to project outward. Cut about 1/4" below the node you would like to propagate. You can choose to create a 1-node cutting, 2-node cutting, etc. The more nodes in one cutting, the more vine-like the plant will be. Fewer nodes will create bushier plants.
For plants like Tradescantia Zebrina, or on longer, vining cuttings, you can prune off the bottom-most leaves to encourage even more growth (sort of like getting a trim to make your hair grow faster). You always want to ensure that leaves too close to the node are removed, as they will rot if submerged under water in the glass vessel, and water propagation is all about a race of root before it rots.
Note: Nodes are commonly found in vining plants such as pothos, philodendron, begonia, monstera, arrowhead tradescantia, etc. There are several exceptions to this propagation rule of nodes- one prime example being peperomia. Peperomia prop well just by cutting anywhere on the stem (allow for enough length on the stem to support the cutting), and little peperomia babies will begin forming and shooting out while under water.
Take your cuttings, wash the leaves (to clear them of any dust that may be inhibiting photosynthesis, and thus, plant growth), and place cutting in glass vessel, with the node submerged under water. Water should be room-temperature, and preferably filtered (I use a portable Brita). If you cannot filter your water, some other options are leaving the water out overnight before starting propagation, to allow some of the chlorine to evaporate out, or simply setting a bucket outside and collecting rainwater the natural way! Plants thrive at a pH of 5.5-6.5, so this will vary depending on where you live and what your water source is.
When water is added to receptacle, put the set-up in a spot that receives moderate indirect light. Avoid intense, direct light or too low of light.
Note: Roots are accustomed to growing in the dark! I have been experimenting with rooting plant cuttings in both glass vases and opaque mugs, with slightly longer/larger roots when kept in an opaque receptacle! Furthermore, when too much light hits water, it leaves the set-up susceptible to mold growth. This is another reason I am starting to prefer opaque receptacles!
Patiently Wait & Maintain
This part is difficult, but stick with it! Monitor root growth, and perhaps designate a day of each week to refresh the water in the propagation container! Remember, one of the ingredients plants need to thrive is oxygen. This can be supplied by refreshing the water every few days, introducing new oxygen and keeping the plant from rotting.
Typically, most aroids are ready for transplanting to soil or LECA within 4-6 weeks (after the roots are an inch or longer). At this point, you will pot your cutting, water it, and place in bright, indirect light once again. I highly recommend Superthrive for this transitioning part. :)