Although foliage remains partially active among many evergreen species consumption of moisture is greatly inhibited as weather conditions cause the stomata (pores on foliar surfaces) to remain closed much of the time. Evapotranspiration (evaporation of moisture from foliar surfaces) is consequently inhibited. (I hope that is not too technical.)

Even species that insist on remaining active do not use as much moisture, simply because it can not evaporate as it would during warm, dry weather. Anyone who dries laundry on the line knows that cool air can not absorb as much moisture as warm air. Humid air that is already partially saturated with absorbed moisture will absorb even less. Air that is both cool and humid is Maytag weather.

Irrigation should always be relevant to weather conditions. Superfluous water is not only wasted, but can cause or enhance serious diseases. Many fungal diseases and some bacterial diseases proliferate in moist or nearly saturated conditions. Soil saturation does not only affect roots within the soil, but may affect any plant part in direct proximity to ambient humidity caused by saturated soil below. Such diseases are more apparent in the endemic, mild climate, because of the preferred combination of cool, moist weather and mildly warm weather through winter.

Soil type, drainage, exposure and irrigation requirements of plant species present should also be considered with weather conditions when adjusting irrigation frequency and duration. Sun exposure changes with the seasons as the sun is out fewer hours of the day than during summer and at a lower angle in the sky (passing through more of the atmosphere than otherwise). Conversely to spring, it is usually safer to risk inadequate irrigation than to irrigate too generously.