Cuttings rot in water primarily because of bacterial growth in the water around the cut stem. A cut stem provides an entry point for bacteria, and stagnant warm water is an ideal environment for bacterial colonies to develop and attack the soft tissue. The most common causes are not changing the water frequently enough, using a container that does not allow light to reach the water (which promotes algae and bacteria), taking the cutting from unhealthy or diseased stem tissue, or submerging leaves rather than clean stem in the water. Most water propagation failures from rot are preventable with clean containers, regular water changes, and ensuring only clean healthy stem is in contact with the water.
Bacterial Rot in Stagnant Water
The most common cause of rotting cuttings is bacterial growth that accelerates when water is not changed regularly. Water that has sat unchanged for more than one to two weeks in a warm room accumulates bacteria and becomes depleted of dissolved oxygen, both of which promote stem rot. The fix is straightforward: change the water every five to seven days, rinse the container and the stem base at each change, and use clean water (filtered or room-temperature tap water that has been left to stand for a few hours works well for most species).
Clear glass containers in bright indirect light are preferable for water propagation. Light reaching the water promotes a small amount of photosynthetic activity that inhibits anaerobic bacterial growth. Opaque containers in dark positions promote exactly the conditions that lead to rot.
Submerged Leaves Causing Rot
Leaves submerged in water rot quickly and introduce the bacterial population that then spreads to the stem. Before placing a cutting in water, remove all leaves from the section of stem that will be submerged. Only clean, bare stem should be in contact with the water. Leaves above the waterline are fine and continue photosynthesising to support the cutting.
Taking the Cutting from Unhealthy Tissue
Cuttings taken from stems that are already diseased, soft, or damaged will rot in water regardless of how carefully the water is managed. Always take cuttings from firm, healthy green stems. Avoid stems that already show any softness, discolouration, or lesions. If the parent plant has been overwatered or has root rot, the stems may already carry bacterial or fungal inoculants that accelerate rot in the cutting. See our guide on root rot in houseplants for what to look for in parent plant health.
Too Long a Stem Submerged
The submerged section of the cutting should be just enough to keep it stable and cover the node from which roots will emerge. Typically, 2 to 4cm of clean stem in the water is sufficient. Submerging a long section of stem provides more surface area for bacterial attack without producing more roots. Keep the submerged section short and clean.
When to Consider an Alternative Propagation Medium
If cuttings consistently rot in water despite correct management, switching to sphagnum moss propagation often resolves the problem. Sphagnum moss has mild antibiotic properties that suppress bacterial growth while maintaining the moisture level needed for root initiation. Insert the cutting into damp (not wet) sphagnum moss with the node in contact with the moss, cover with a clear humidity dome, and place in bright indirect light. Our Sphagnum Moss is the standard choice for this approach.