@ECOBEARD I appreciate your curiosity about this topic. Good news! We are currently developing a “dynamic crop coefficient” feature we will release this spring (2022) that will automatically provide specific crop coefficients for each month of the year for all crops. We’ve combed the available research to come up with crop coefficient curves that are specific to months, plants, and regions. For example, the table you posted with the Meyer 1985 data provides coefficient values for cool and warm season grasses in a mediterranean climate, so most Rachio controllers in mediterranean parts of CA, OR, etc will get those coefficients. However, Rachio controllers in Denver, Seattle, New York, Miami etc will each get their own set of coefficient curves according to their local climate.
This should provide a more accurate watering experience for all our customers, and will hopefully solve some over-watering and under-watering issues that can occur in some parts of the country due to annual average crop coefficients not keeping up with seasonal variability.
We’ll provide in-depth background material when we release the feature (existing customers will have to opt into it, and we’ll explain how). If you want to learn more about the topic, the UC ANR sources posted in this thread are good sources of information.
For anyone curious about crop coefficients for specific agricultural crops, there is a wealth of published research, but it can be laborious to sift through. This page from the UN Food and Agriculture Organization (FAO) has a very comprehensive set of tables for crops organized around growing seasons: Chapter 6 - ETc - Single crop coefficient (Kc). We took this information into account while creating more simplified crop coefficient curves for vegetable and flower garden zones.