Introduction
Phenology is the science of seasonal events and developmental stages in living organisms. In growing practice, it refers to the sequence of physiological stages a plant passes through and the optimal conditions for each phase.
- Vegetative phase: active growth of leaves, stems, and roots; priority — maximum leaf mass and root system
- Generative phase: flowering and fruiting; priority — sugar synthesis, fruit development, and accumulation of secondary metabolites
Why Plants Need Different Conditions at Each Phase
During vegetative growth, nitrogen demand is highest for chlorophyll and protein synthesis. At the transition to the generative phase, nitrogen requirements drop sharply while potassium and calcium demands increase for fruit quality.
Light requirements also change:
- Vegetative phase: DLI 18–22 mol/m²/day is sufficient for active leaf growth
- Fruiting phase: 25–35 mol/m²/day is needed for fruit fill and sugar synthesis
EC also changes:
- Germination: 0.5–0.8 mS/cm
- Active vegetation: 1.8–2.2 mS/cm
- Fruiting: 2.5–3.5 mS/cm
Phases and Their Parameters: The Logic of Transitions
Phase 1: Germination and Emergence (0–7 days for most crops)
Root system absent or minimal. The seed draws on internal reserves.
- EC: 0.5–0.8 mS/cm or plain water
- pH: 5.8–6.2
- Temperature: 22–26°C
- Light: minimal or none for seeds; gradually increase after emergence
Phase 2: Early Vegetation (1–3 weeks after emergence)
Root system and first true leaves are forming. Elevated phosphorus demand for root development.
- EC: 0.8–1.2 mS/cm
- DLI: 10–14 mol/m²/day
- Temperature: 20–24°C
Phase 3: Active Vegetation
Maximum leaf mass growth. Highest nitrogen demand.
- EC: 1.5–2.5 mS/cm (crop-dependent)
- DLI: 16–25 mol/m²/day
- pH: 5.8–6.5
Phase 4: Bud Formation and Flowering (for fruiting crops)
The critical transition point: excess nitrogen inhibits the shift from vegetative to generative phase.
- Reduce nitrogen: switch to a "flowering recipe" where K > N
- Increase calcium and boron for pollen quality and fruit set
- EC: 2.0–2.8 mS/cm
- DLI: increase to 22–28 mol/m²/day
Phase 5: Fruiting and Ripening
Maximum potassium demand for sugar synthesis and assimilate transport to fruit.
- High K fraction in the recipe
- EC: 2.5–3.5 mS/cm for flavour concentration (controlled stress)
- DLI: 25–35 mol/m²/day
- Maintain VPD 0.8–1.2 kPa
For leafy crops (lettuce, greens, microgreens): the fruiting phase does not occur. The cycle covers phases 1–3 and partially 4. Bolting marks the end of the commercial cycle.
Practice: When and How to Transition Between Phases
Transitions are made gradually over 2–4 days. A sharp EC change of 1.0 mS/cm in a single day causes transient osmotic stress.
Transition indicators:
- Early to active vegetation: 3–5 true leaves; stable turgor
- Vegetation to bud formation: first visible buds, or according to crop schedule
- Bud formation to fruiting: visible fruit set and active growth
Three Most Costly Mistakes
Not reducing nitrogen at the transition to fruiting. Excess nitrogen during bud formation causes continued vegetative expansion instead of resource conversion into fruit: small fruit, delayed or uneven ripening, and excessive vegetative mass.
Maintaining low EC throughout all phases "to avoid damage." EC of 1.0–1.5 during fruiting produces fruit low in sugar with a neutral flavour. A controlled EC increase during ripening is standard practice for flavour development.
Not increasing DLI at the transition to fruiting. DLI 16 mol/m²/day, optimal for vegetation, is insufficient for fruit fill and sugar synthesis.
How to Verify That Phase Management Is Correct
- A transition schedule exists for each crop and cycles follow it
- EC and recipe change at every phase transition — they are not fixed throughout
- The first fruit appears on schedule with the correct size and colour
- Flavour at tasting is distinct from "neutral"