Plant care guide
Pothos Water Propagation: Algae, Biofilm, or Root Rot?
Updated · First published
What should you know about algae confusion water propagation for a Pothos?
Green film on the glass, in the water or on the roots of a pothos cutting is usually algae. It looks bad but is not root rot. Rot shows as roots or stem tissue that are brown to black and soft or mushy.
What to do first
Lift the cutting out and gently squeeze a root. If the roots are firm, wash the jar, refill it and change the water once or twice a week. If roots or stem are soft and dark, cut back to firm tissue and restart in a clean jar.
A green tint in your pothos propagation jar looks alarming, but it is rarely the emergency it seems. Algae and root rot are different problems with different fixes. Lift the cutting out of the water and check the roots before you cut anything.
Pothos is one of the easiest plants to root this way. NC State Extension’s pothos profile notes that the vines root easily in water. The University of Nevada propagation fact sheet also lists pothos among plants that root well in water, and advises keeping the water clean and fresh.
Algae, rot or healthy water roots?
| What you find | Most likely |
|---|---|
| Green film on the glass, the water or the outside of roots; roots firm | Algae |
| Cloudy water, roots still firm and pale | Water overdue for a change |
| Roots brown to black, soft or mushy; outer layer slides off | Root rot |
| Soft, dark stem around or below the node | Stem rot |
| Thick, coarse, firm roots | Normal water roots |
Algae. University of Maryland Extension’s page on algae and fungal growth describes algae as simple aquatic plants that form a greenish layer in moist conditions. It notes that their growth isn’t usually harmful to plants.
Root rot. UMD’s root rots page describes rotted roots as brown to black and soft or mushy. The outer part of the root pulls away easily and leaves a thin thread behind. That texture test is more useful than colour alone.
Normal water roots. Iowa State University Extension’s stem cutting guide explains that roots formed in water are coarser than roots formed in rooting media. Thick roots are not a warning sign.
If it is algae
- Set the cutting in a glass of clean water while you work.
- Wash the jar, rinse it well and refill it with fresh water.
- Rinse the roots gently under running water. Do not scrape or cut firm roots just because they look green.
- Put the cutting back with the node under water and the leaves above it. Missouri Botanical Garden’s guide to rooting cuttings in water says any part below the water should be free of leaves.
- Change the water once or twice a week, as Iowa State advises. Never let the level drop far enough to expose developing roots to air.
If algae keeps coming back, remember that algae are plants and need light. A coloured jar, or a paper sleeve around clear glass, cuts the light reaching the water. Keep the leaves in a bright spot out of direct sun, as the RHS cuttings guide suggests.
Clean water and a clean jar are the fix. None of the sources we used call for chemical treatment of algae on a cutting.
If the roots or stem are rotting
- Cut away soft, dark roots with clean, sharp scissors. Keep only firm tissue. UMD advises taking cuttings only from healthy tissue.
- Check the stem. If it is soft at the node, recut above the damage. UNH Extension’s cuttings guide explains that the node is where new roots form, so the new cutting needs a sound one.
- Cut just below a node. Missouri Botanical Garden warns that a stub of stem left below the node often rots.
- Restart in a clean jar of fresh water and change it on schedule.
If rot keeps recurring, see our pothos node selection guide. For rot on a potted plant, see the pothos root rot guide.
When to move the cutting to potting mix
Iowa State suggests transplanting once roots are about 2.5 cm (1 in) long. Missouri Botanical Garden suggests 2.5–5 cm (1–2 in). The RHS expects most cuttings to root in 3–4 weeks.
Expect a short adjustment. Iowa State notes that water-grown roots are not well adapted to potting soil. Newly potted cuttings may wilt, drop leaves or show browning before they settle. The University of Nevada also warns that cuttings can go into shock after the move.
Pot into a small container with drainage holes. Water until it runs out of the base, then empty the saucer. Missouri Botanical Garden advises against leaving the pot standing in water. Keep care steady for the first few weeks.
Our pothos propagation guide covers taking cuttings. The complete propagation guide compares water and soil rooting.
References
- Iowa State University Extension: How to Propagate Houseplants by Stem Tip Cuttings
- Missouri Botanical Garden: Rooting Cuttings in Water
- RHS: How to take cuttings from houseplants
- University of Nevada, Reno Extension: Propagating Houseplants (FS-98-92)
- University of Maryland Extension: Algae and Fungal Growth on the Soil of Indoor Plants
- University of Maryland Extension: Root Rots of Indoor Plants
- NC State Extension Gardener Plant Toolbox: Epipremnum aureum
- UNH Extension: Tips on How to Propagate Houseplants from Cuttings
How this guide was put together: Iowa State University Extension, Missouri Botanical Garden, RHS, University of Nevada Extension, University of Maryland Extension, NC State Extension and UNH Extension guidance.