I’m not an expert with emitters, and there’s a spreadsheet here that can help with that. But in my experience, with emitters, you usually know how much water a plant or plants need. So you can calculate from that, backwards, to what the Nozzle Inches per Hour needs to be. There are two ways. I’ll make a simplified example:
You have 5 5-gallon plants and 5 3-gallon plants, and I’ve heard that such plants require 1 gallon of water per week per plant size in gallons, and that this gives about 1" of water per week.
Method 1: You know how many and what size emitters you have. Say you have twenty 1 GPH emitters, that’s a total of 20 GPH. Further, from above, 1" of water per week is 5x5+5x3= 40 gallons. So you need to water for 40/20 = 2 hours per week. Working backwards, 1" of water in 2 hours gives a Nozzle Inches per Hour of 1/2 = 0.5 "/hr.
Method 2: If you have a bunch of emitters and are not sure how many or what size they are, you can measure the GPM of the zone using your water meter. Water for say 10 minutes, taking gallon readings before and after, to calculate GPM and GPH. If you’re watering the entire area where you shrubs are located, then you can use that area and calculate in/h in the normal method. If not, again, you need to know the water requirements for the plants, and calculate as above.
The main thing is: For Lawns, you’re calculating in/h based on flow of water divided by area (or from tables of typical values). With shrubs, where you’re often not watering the entire area, you have to calculate an equivalent in/h, based on the crop’s water needs and how much water your system supplies. The result doesn’t mean much, but it’s at least one method of determining this important Nozzle Inches per Hour setting in Rachio.
Hope this helps.