Collection: Propagation

The node goes under water, the leaf stays above it

One rule carries nearly all of water propagation. The node, meaning the small bump on the stem where a leaf joins it, has to sit under the water. The leaf has to stay above it. Get those two facts right and most common houseplants root without any further help.

Roots come out of the node and nowhere else. A length of bare stem sitting in water with no node on it will never produce a root, however long you wait, and that accounts for a fair share of cuttings that sit clear and green for a month doing nothing at all.

A submerged leaf does the opposite kind of damage. It softens in about two days, then rots, and the rot feeds the bacteria that turn the water cloudy and go on to attack the stem. Strip every leaf that would fall below the waterline before the cutting goes in, and keep two or three leaves at the top, because those are what feed the cutting while it has no roots.

Where to cut, and how to spot a node

On a pothos or a philodendron the node is a slightly swollen band on the stem, often a shade browner than the rest, with a leaf stalk and sometimes a small brown nub growing from it. That nub is an aerial root, and a cutting that already has one roots faster than a cutting that does not.

Cut about 1/4 in (6 mm) below the node with clean scissors or a blade. Leaving that short stub protects the node itself from bruising, and cutting further down leaves you with dead stem sitting in the water. Wipe the blade with rubbing alcohol between plants, since a blade carries a problem from one plant to the next.

Take a piece with at least one node and two leaves. Longer cuttings are not better. A single node with two leaves roots faster than a 12 in (30 cm) length with five, because the cutting is supporting less growth on no root system at all.

What roots in water, and what only pretends to

Water works for soft stemmed tropicals and works badly for anything that stores water in its own leaves. Succulents and cacti rot in water before they root, and the same goes for most woody herbs past their first green growth.

The vessel sets how often you have to think about it

Glass is the point here. You watch the roots come, and more usefully you see the water go cloudy on day four instead of finding out a week later. The shape matters for one practical reason: how much water sits in there, and therefore how many days pass before the node is dry.

A narrow neck also does the job a bud vase does for a flower. It holds a single cutting upright with its node in the right place instead of letting it slide down and float sideways, which is what happens in a wide jam jar with one stem in it.

Light, warmth and what to fill it with

Bright indirect light, meaning a spot where the cutting can see the sky but the sun never lands on the glass directly. Direct sun through a clear vessel warms the water, and warm water in a small volume grows algae in under a week.

Room temperature does the rest. Cuttings root fastest between 65 and 75 F (18 to 24 C), and a cutting on a windowsill that drops to 55 F (13 C) at night in winter simply stops. If nothing has happened in three weeks and the stem still looks healthy, the room is usually too cold rather than the cutting being dead.

Tap water is fine in most places. If yours is heavily chlorinated, leave it standing in an open jug overnight and the chlorine gasses off. Skip softened water, which carries sodium, and skip adding fertilizer while the cutting is rooting: it has no roots to take it up and it feeds algae instead.

Changing the water without wrecking the roots

Change it every three to five days, and change it rather than topping it up. Topping up leaves the bacteria in place and raises the waterline onto stem that was dry, which is the section least able to cope with being wet.

Hold the cutting in place with two fingers, pour the old water off, and refill with water at room temperature. Cold water straight from the tap on new roots is a small shock every time. Once roots reach an inch or so they are brittle, so pour rather than tipping the whole thing into a sink.

Every second or third change, clean the glass. A film builds on the inside of a propagation vessel exactly as it does in a flower vase: mineral haze from hard water plus a slick layer of bacteria. White vinegar and a bottle brush handles both. For a test tube too narrow for a brush, uncooked rice and a hard swirl scours the inside.

Rot, algae, and cuttings that do nothing

Rot shows as a soft brown or black stem end that feels slimy between your fingers, and the water usually smells before it looks wrong. Take the cutting out, cut back into firm green tissue above the damage, rinse it, and start again in a clean vessel with fresh water. Rot never reverses, so cutting early saves the cutting.

Green algae on the glass is untidy rather than dangerous, and it means sun on the water. Move the vessel back from the window. Roots that have gone brown and mushy are rot; roots that have gone brown and stayed firm are usually fine, since some species root brown from the start.

A cutting that sits green and healthy for six weeks and does nothing is nearly always a cutting with no node under the water, or a room under 60 F (16 C). Lift it out and look at the submerged section. If there is no node down there, take a new cutting rather than waiting out another month.

Moving to soil, or leaving it where it is

Move a cutting to soil once the roots reach 2 to 4 in (5 to 10 cm), and sooner rather than later. Water roots and soil roots are built differently: water roots are fine, white and brittle, adapted to taking oxygen straight from the water, and a cutting that grew 8 in (20 cm) of them loses most of that work in the move.

Pot into a small container, no larger than 4 in (10 cm) across, and keep the soil properly damp for the first two weeks rather than letting it dry between waterings. The cutting is switching root systems and cannot survive drought during the changeover. After a month, water it like any other plant.

You can also leave it. A pothos will live in a glass of water for years, growing slowly, so long as you change the water and it gets light. It will never match one in soil for size, which is the honest trade. That is the appeal of this whole category: the cutting costs nothing, the water costs nothing, and the only thing you actually buy is the vessel that holds them in the right relationship to each other.