@robertokc – that’s a nice website!
@KJones7440 – I think that the Water Application Rate Calculator at the Washington State University website might be something else to look at especially if your drip is not installed as a grid but as an emitter at each plant with some random spacing.
First though, the area setting on Rachio is only used to estimate water usage. That value will not impact how the plants are watered. HOWEVER, for drip, you do want to know the estimated area that needs to be watered on an individual plant basis (more in next paragraph). Root depth is important but Rachio’s defaults for annuals should be a good start. You can estimate this based on the depth of the pot the plants came in and maybe add a couple inches more or Google for the average root depth of those plants. Crop coefficient is important but it is harder to get that information especially for non-food crops. The rachio defaults for crop coefficient will probably be the best place to start and if the plants seem to need more water, add 5%-10%. If they seem overwatered, subtract 5%-10% from the crop coefficient. You’ll want to monitor and adjust until your plants seem happy. I would not change allowed depletion, that’s pretty standard. So that brings us to Nozzles Inches Per Hour, the most critical part.
If using the Water Application Rate Calculator to calculate Nozzle Inches Per Hour, you’ll need to choose whether to use the average area of all plants on the drip or only use the area of the most (or least) water hungry plant or the area of a representative plant. To get at watered area, you’d measure the radius from plant stem to its outer leaves, then use pi*radius^2 to get area of that plant. You could do this for each plant and then average the areas – do not use the area for the entire planting bed. You want only (roughly) the area of roots you need to watered. The nozzle rate is going to be necessarily calculated for a single emitter rate, so you’ve made it easy on yourself by selecting only 0.5 GPH for all plants. Excellent! The Water Application Rate calculator is very flexible with all kinds of units available – so you if you measure the radius in inches, be sure to select inches^2 for the resulting area. Then enter in your 0.5 GPH and select GPH. Does this make sense?
So a representative single plant may have a 6" radius from stem to the where the leaves end. So pi*6^2=113 in^2 or 113 square inches for a single plant. Enter that value into the calculator, being sure to select square inches as the area unit. At 0.5 GPH, the calculator says 1.02 in/hr for that representative plant. If on average plants on that drip line have about 6" radius, then the 1in/hr would a good choice for all plants. As the plants grow, you could recalculate the nozzle inches/hour by remeasuring the plant radiuses. Once they’re mature, you won’t have to adjust as much (hopefully).
For new plants fresh out of the pot, you may just want to use the surface radius of the rootball.