Why are my cannabis clones not rooting?

Cause 1: Temperature too low

Cannabis clones require 75-80°F air temperature and ideally 75-78°F medium temperature to root in 7-14 days. Cold rooting medium (below 70°F) slows root cell division to a crawl — clones may sit for 21+ days without producing roots. The fix is a heat mat under the rooting tray with a thermostat set to maintain medium temperature in the target range. Heat mats designed for seedling propagation are inexpensive and dramatically improve rooting success rates.

Cause 2: Humidity too low

During rooting, cannabis clones survive on moisture absorbed through their leaves rather than through nonexistent roots. Below 60% relative humidity, the clone transpires faster than it can absorb moisture, leading to wilting and eventually death. The fix is a propagation dome or humidity tent over the cutting tray, with vents partially open to allow air exchange. Mist the inside of the dome 1-2 times per day with pH-adjusted plain water to maintain humidity. Open the dome vents progressively as roots develop and the clone transitions toward standard ambient conditions.

Cause 3: Light intensity too high

Cannabis clones being rooted under full-power flower or veg lights almost always struggle because the strong light demands more transpiration than the rootless clone can sustain. Drop to 100-200 PPFD during the rooting phase — T5 fluorescents, low-wattage LEDs, or significantly raised flower lights all work. After roots are visible, ramp up gradually.

Cause 4: Rooting medium issues

Overwatered rooting medium prevents oxygen from reaching the cut stem, which slows or prevents callus formation (the precursor to root development). Conversely, dry medium starves the cutting. Ideal moisture is evenly damp throughout but not waterlogged — squeeze a Rapid Rooter or rockwool cube and a few drops should release, not a stream. Compacted medium also blocks new roots from extending; lightly fluff or replace medium that has been heavily compressed during transit or handling.

Cause 5: Stressed mother plant

Cuttings taken from stressed, sick, or weakened mother plants often fail to root regardless of environmental conditions. Mothers that are nutrient-deficient, pest-infested, root-bound, or carrying pathogens (especially HLVd) produce cuttings with reduced vitality. If you've ruled out the four environmental causes and clones are still failing, the problem may be the source. Tissue-cultured stock from verified breeders is the most reliable starting point for serious propagation.