Foxtailing is when buds keep stacking new calyxes upwards and outwards in thin spires, rather than swelling into dense colas. The result looks like a fox's tail or a spiky tower. It has two broad causes. Some cultivars foxtail naturally, especially long-flowering, narrow-leaflet lines, and that is a heritable trait. Others foxtail only under stress, most often heat or excess light at the tops nearest the fixture.
In practice
Telling them apart: genetic foxtailing appears throughout the plant, including lower buds that never got hot. Environmental foxtailing concentrates at the canopy top, often alongside bleaching, and appears after a run of high leaf temperatures (above about 30 °C / 86 °F) or PPFD above about 1,200 µmol/m²/s without matching CO2.
Fixes for the environmental form: raise or dim the light, lower canopy temperature, improve airflow over the tops, and keep VPD in range. Late in flower, some cultivars push a final flush of foxtails as they ripen; check trichomes before blaming the room.
Foxtailed buds are not necessarily lower quality, but stress foxtailing usually comes with reduced density and bag appeal.
Don't confuse with
- Light stress (bleaching): loss of pigment; often happens alongside environmental foxtailing.
- Re-veg: new leafy growth from buds after a photoperiod disruption, not stacked calyxes.
Botanically, the sepals of a flower; in female cannabis a thin, reduced perianth on the ovary, though growers use the word for the resinous bract.Light stress is damage when leaves or buds absorb more light than they can use or dissipate, showing as bleached white or yellow tops nearest the fixture.Leaf temperature is the actual surface temperature of a leaf, which often differs from air temperature by 1–3 °C depending on light source and transpiration.Photosynthetic photon flux density: the number of PAR photons landing on one square metre each second, in µmol/m²/s; the standard measure of light intensity at the canopy.Vapour pressure deficit: how much more water vapour the air could hold at its temperature, in kPa; it is the main environmental driver of transpiration.Feeding only plain water for days or weeks before harvest to "clean" the plant; GenetixBay rates it a Myth that harms yield, unlike a root-zone salt flush.A hair-like outgrowth of the plant's skin; in cannabis the glandular types make and store the resin holding cannabinoids and terpenes.The daily length of light versus dark; photoperiod cannabis flowers when nights grow long enough, rather than at a fixed age.Heat stress is damage or slowed growth when leaf or canopy temperature rises above what the plant can handle, typically above about 30–32 °C (86–90 °F) in cannabis.In growing, temperature usually means grow-room air temperature; cannabis grows best around 24–28 °C (75–82 °F) by day and a few degrees cooler at night.
