Probably the most crucial concept of the game is plant growth. And this is strongly tied to the weather itself. Weather carries the randomness but also forces a player to make strategic decisions. Plant growth is the execution. It works as well as the weather allows it.
Each turn, every crop is evaluated against environmental factors, and each plant has a different response profile. Weather factors are:
Temperature
Rainfall
Sunlight
Day length
But rainfall is not used in calculation. The actual factor used in calculations is its derivative: soil moisture. It takes field water management into consideration (go to the devlog #4 for more info!). Also, soil quality affects the growth. Moreover, there are other events derived like snowfall, frost damage, and drought which are actual events in game affecting plants. Calculations are created to partially follow the Liebig's Law of the Minimum. One terrible factor drags down the whole result, no matter how perfect the others are. A heat wave can stall a well-watered, perfectly fertilized field.
Identical fields planted a few turns apart can produce very different results. A late frost, an unexpected dry spell, or planting the wrong crop for the season creates genuine variety.
Crops track two values independently:
Readiness
Health
Readiness increases each turn based on the combined growth factor. When it reaches a certain point, it's ready for harvest. But crops can go beyond, resulting in overripeness. Health drops when conditions are dangerous: frost, extreme heat, drought, waterlogging, etc. Low health reduces the yield. A crop can be ready but damaged, giving a fraction of the expected harvest.
Crops move through phases (dormant, vegetative, producing, ready). Each phase has its own tolerance profile and optimal ranges of the factors. The phase determines which set of environmental tolerances apply. Transitions are triggered by readiness thresholds. A crop switches from vegetative to producing at around 40% readiness, and becomes ready for harvest at 100%. Some crops have an additional requirement: winter wheat, rye, and triticale need vernalization, a period of sustained cold exposure (several consecutive turns below 5-7C). Until vernalization completes, the crop stays vegetative regardless of readiness. Warm weeks during winter can interfere, delaying the transition.
Trees work slightly differently from annual crops. After planting, a tree needs months to mature depending on species. During this time the tree produces nothing. Once mature, a tree produces fruit every season without replanting. Each turn, fruit readiness accumulates based on weather conditions, just like annual crops. When ready, the player harvests the fruit and readiness resets to zero. The tree stays and begins producing again next turn.
A player will not need to fight the weather on its own. A short-range forecast (a few turns ahead) is available. It shows the general trend, not exact values. Some in-game skills will provide better forecasts for a player.