Tree roots should “chase” the water to a depth of 18-24 inches. It takes hours for the water to percolate down to that depth. With more frequent and shallow watering, your trees are more at risk.
After the next time you “short” water, dig into the earth just inside the outer edges of the tree canopy and observe how deeply the water has soaked in. You will be shocked, especially if your soil has a moderate to large percentage of clay in it.
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I’ve been reading up some literature on fruit tree irrigation and here’s what I’ve found from the University of California (very likely mostly applicable to CA’s conditions):
Irrigation - The California Backyard Orchard (ucanr.edu)
Drip Irrigation
The theory and practice of drip irrigation is to provide just what the tree needs every day. Not enough water is applied to leave any in storage in the soil for the next day, so it needs to be watered again the next day. Drip irrigation is a good delivery system because it only wets a small area so that weed growth is limited and the system is easily adapted to many landscape situations. Fortunately only a small fraction (10–20%) of the root area needs to be watered in order to achieve good results.
[…]Mini/Micro-Sprinklers
Mini-sprinklers are small sprinklers with the water delivered through drip irrigation tubing. Each individual mini-sprinkler usually delivers about 10 gallons per minute or 10 times the average drip emitter. The mini-sprinkler system is typically run twice to three times per week with some water held in the soil in storage. Run times can be calculated (from the Guide), multiplied by number of days between irrigation intervals. Care must be taken to investigate the depth that the irrigation water is reaching for mini-sprinklers since some of them shoot the water so far that they would have to run continuously for days in order to water down 24 inches.
Most fruit tree roots are located between 6 inches and 24 inches of the top of the soil. This is also the area with all the nutrients (topsoil) and the oxygen. Keep this area moist at all times and really focus on maintaining adequate moisture there. The old adage of forcing the tree roots down deep is just that it is forcing the tree and causing stress. Home orchard trees that are on deep soils can get by with less intensive irrigation management because the tree roots are deeper and there is a buffering capacity for drought stress. Shallow soils need to be managed much more intensely with frequent lighter irrigations.
Sprinkler Irrigation
Sprinkler irrigated trees use the same amount of water as drip irrigated trees (which is based on how hot it is) plus an additional 20% for loss to evaporation and non-uniformity of application. The real difference is that with sprinkler irrigated trees, more water is applied at once, it is stored in the soil for 2-3 weeks before the next irrigation, and the entire area is watered. When the whole area under the trees is irrigated, water can not be saved based on tree size. Weed growth also covers a much greater area.
Another important difference for sprinkler irrigated trees is that soil rooting depth (volume of soil) and soil water holding capacity (soil type, sand or clay) becomes important since water is stored in the soil. If trees are over irrigated water is lost beyond the root zone. Under irrigation is usually caused by not running the sprinklers long enough to wet the entire depth of the root zone or miscalculating the amount of water stored in the particular soil type and going too long between irrigation intervals.
For sprinkler irrigation, water is not applied daily, but on a periodic basis to fill the soil, which acts as a storage reservoir for water available to the plant. Soil type and rooting characteristics are very important. Recent research shows beneficial results from irrigating at or before 50-75% depletion of the (soil-stored) available water, then applying what has been used + 20% for efficiency loss.
Good source and great information.
More questions (edited).
- Noticing start time issues using ‘end before sunrise’ and ‘end at a certain time’. Both seem to start the day before even if the run time is only a few minutes. This pic is of the scheduled run for June 16th using end before sunrise, starting on the 15th.
- What other factors are being used for the start times (and how)? Does ‘end before sunrise’ prevent its own schedule from starting a cycle again during the same day? For example say there are consecutive daily cycles (some long, some short) in the calendar, any short cycles in there will start the night before because the next long cycle is pushing their start times back? Until there’s a day break to reset itself (at least for short cycles). Or is temperature, etc, playing a factor in start times? Like if its really hot and dry will it start the night before to avoid higher daily evap rates?
- Besides dividing water per application by evap, what else does Rachio use to calculate days between watering? That calculation obviously isn’t set in stone since I find the same zones being watered on consecutive days despite the evapotranspiration and water per application staying the same. I understand it uses allowed depletion too but the soil moisture shouldn’t be going 0% everyday if the evap and water per application aren’t changing.
Now starting today and on the calendar for the next two weeks, all ‘end at sunrise’ start times are around 530 pm. The longest cycle only goes until about 230am, most end before midnight. I guess end before sunrise just means it’ll start anytime before the next sunrise. Maybe they should rename it? I was thinking it had something to do with avoiding high temperature but it’s almost 530pm here, 97 degrees and full sun.
How does it calculate these start times? I would really like to know!
The end before sunrise time is calculated based on all the zones in that schedule running back to back, if 1 zone doesn’t need water, that zone’s run time will cause the actual end time to be earlier.
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Thanks for the reply! Why though was Flex Daily two weeks ago starting around 2am, then this past week around 10pm, now moving to around 5pm? Same total duration. I was hoping it was calculating some other things to find the most optimized watering times but sounds like end before sunrise is not going to be what I want.
Hello, how did you set this up? I’d like to adjust the duration and frequency manually because of how complicated the Flex features are; but also be weather aware.
Hi there! I use a fixed schedule and make sure that Seasonal Shift and Weather Intelligence are enabled.
I set up my zones using the times that I know will work. After that, the Rachio took over.
One day, we had some really high winds so the Rachio notified me that it would skip watering that day. Then, about a month ago, Rachio notified me that it was increasing watering by 1 minute each zone for a Seasonal Shift.
The other feature that I really like is the Quick Run. Sometimes the weather is so freaking hot 
that parts of my yard are suffering. I just go to my iPhone and do a Quick Run on whatever zone needs a refresher!
Does that help?
I am still using Flex Daily. With every setting fine tuned its running very well. I did however stop using ‘end before sunrise’ as the start times were not ideal. I switched to a fixed start time around 3am, that way if it does run all of my zones it’ll still end mid-morning before its too hot.
If you’re looking to adjust durations and frequency yourself then I’d go with a fixed schedule to cover the most basic watering needs and use quick run for any additional time you need to water. You can still turn on all of the weather delay features using fixed schedules.
Thanks, I think the myriad advanced settings that give no indication on how they affected the only two parameters we actually control; runtime and period; are a masterclass at over-egging the pudding. Since my plants are brown and wilting I need more water, and I’ll have to DIY as the Rachio UI is complicated to the point of self-defeating.