I’ve been considering the Zimmerman method, but it seems to me that during times of shallow watering, it may encourage shallow root development. Or not?
The city I live in only allows watering twice per week, so optimally, any calculations should look to the past week and see how much it has rained. Assuming I wanted to hit a target of one or more inch per week, but only water deeply when I do water, is it possible to look back one week prior on each watering day and calculate if the rainfall has equaled one inch? If it has, it would skip watering, but if not, it would water the full amount, even if the cumulative is more than one inch.
The algorithm only looks at the previous day (not the previous weeks’ rain amount). The only way to go that far back in history is either that the Wunderground API has to provide that history data, or you have to integrate ShawnHarte’s ET-based algorithm, which logs the data onto SD card, essentially creating a history of data by the controller itself.