Tacoing or canoeing is an upward fold of the leaflet along its midrib so the edges point toward the light. Plants do this to reduce the leaf area facing intense light and to cut water loss when leaves are hot or the air is dry. Leaf temperature depends on air temperature, radiation, airflow and transpiration (Nelson and Bugbee 2015).
In practice
Check where it occurs. At the top of the canopy, under the fixture or in hot spots, it points to heat, high VPD or too much light: measure leaf temperature, air temperature, RH and PPFD. Across the whole plant, with spotting or distorted growth, look at roots, calcium delivery and watering.
Don't confuse with
- Leaf clawing: tips hook down, not edges up.
- Praying leaves: whole leaves angled upward but flat, a sign of a happy plant.
- Broad mite damage: twisted, glossy new growth.
One of the separate serrated blades that make up a palmate cannabis leaf; a mature fan leaf typically has five to eleven leaflets.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.The evaporation of water from a plant, mainly through open stomata, which pulls water and dissolved nutrients up from the roots.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.Relative humidity is the water vapour in air as a percentage of what it could hold at that temperature, so the same RH dries plants differently at different temperatures.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.Leaves whose tips hook sharply downward like a claw, usually on dark green leaves; a classic sign of excess nitrogen, and also seen with waterlogged roots.Polyphagotarsonemus latus, a microscopic tarsonemid mite whose toxic feeding twists, glazes and stunts new growth; often mistaken for calcium deficiency or heat stress.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.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.
