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Senior Member


Monday, April 23rd 2012, 12:08am

ESP-SMT questions

I had a Rainbird ESP-SMT controller installed by a contractor...good job on the install, but my questions to the several contractors I got bids from (including the one that did the install) showed me that contractors in this area haven't installed enough of them to really understand how they're supposed to be configured.

I've got a few questions that I hope the good folks here have enough experience to answer..

1. The install instructions clearly say that the rain sensor/weather station should be installed "in a location that receives afternoon sun in order to measure the daily high temperature (South or West exposure is ideal): and "Do NOT install the sensor where it will be located in the shade in the hottest part of the day."

So that's where the sensor is, at the peak of the garage where it gets full afternoon sun. This means that the temperature sensor is reading between 5-10 degrees hotter than the actual high temp for the day! I suspect once summertime comes it will be even farther off. Why wouldn't it make more sense to put the sensor where it will be in the shade during the hottest time of the day so it will read the actual high air temp rather than the artificially high temp that the sensor picks up because it's baking in the sun?

2. Today I checked the controller and it said "Soaking" with "Time Remaining: 89 minutes." What does this mean?

3. With a typical ("dumb") controller, I always have the zones come on in the early morning (say 4am) so that the irrigation will be complete before the day gets too hot (to lessen evaporation). With a smart controller like this, does it make sense to restrict the irrigation window to, say 4-8am for the same reason?

4. How important is it to actually figure out the type of soil I have? The installer just selected "Clay Loam" for all zones, which seems to be an "in the middle" setting.



Monday, April 23rd 2012, 8:25am

1. Part of the logic is based on 'worst case' conditions. If you are in a residential area then the part of the yard that gets the biggest beating is hit by direct sunlight,combined with other conditions to make it hotter, such as concrete retaining and reflecting heat, as by the street, the corner by the street and driveway, etc. This area gets heat from the sun, heat from reflected rays and the concrete stores heat so it is baked even after the day starts cooling. This is your hardest area to maintain.

2. Soaking. In sloped areas it is common to run the system for a few minutes, put a soak delay in, and run it again. The soaking cycle gives the soil time to absorb the water. Short run times with a soak cycle are better than one long run time leading to run off.

3. Sometimes smart one way is not really smart the other. Delaying the watering can push the time back until heat of the day. The controller doesn't take that into consideration. I'd try a water window myself, see what happens. Assuming you don't have too many zones to make it work.

4. Clay loam = good if you have it. Sands absorbs water quickly but can't retain it. Clay absorbs slowly, leading to possible run off, but holds it a good while. Clay loam is the best of both worlds. Your controller will depend on this setting for its changes, so accuracy does make a difference.


Senior Member


Monday, April 23rd 2012, 9:55pm

Thanks for your quick reply.

#1. Perhaps then for me it makes sense to move the sensor to where it ISN'T in full sun during the heat of the day. My concrete driveway is almost all shaded by a large tree, so it gets filtered light for 1/2 a day, then is in the shadow of the house the rest of the day. As for the asphalt street, it's separated from a bed by a 1 foot wooden wall, and it, too, is only in sun for the first half of the day. The back yard/beds are in shade for the 1st half of the day, and then partial sun the rest of the day, and have no street or hardscape to reflect and hold heat.

#2. Makes sense. But an 89 minute soak period? That zone is set to 8% slope, but still, 1.5 hours seems a huge soak time!

#3. Based on your comment, I'll keep the watering window. Is there a way to tell with the smart controller whether the full desired cycles ran completely as the controller, in its infinite wisdom, decides? And, better to push into the day (bad for evaporation) or earlier in the am/night (worse for things like diseases, mold, etc., right?)

#4. Looks as if I should do some digging to test the kind of soil I actually have.

New question:

#5. Is there a way to determine, other than by poorly performing plants, whether the amount of water is reasonable? The old "1 inch per week of water for lawns" seems like a way too general rule of thumb, given all of the other considerations.

Thanks again!


Tuesday, April 24th 2012, 8:29am

1. Try it. You'll know soon enough. The science in this industry is not always as exact as they'd like you to think.
2. Uh, yup. 89 = long.

Page 23 of the manual has a brief synopsis. Then start on page 76. Might want to stock up on caffeine first.

3. Coin flip. I hate nighttime watering. Also hate full sun evaporation. Of course, some days I hate my lawn too....

4 and 5. Check out an article HERE. It's a how to get answers thing. It's brilliant but, then, I wrote it.

Central Irrigation

Supreme Member

Posts: 371

Location: Central Minnesota


Tuesday, April 24th 2012, 9:00pm

FYI...There is a function that allows you to increase or decrease a particular zones settings by a percentage if you feel it waters too much or too little. Also, the zone's parameters should be set according to sun/shade, soil type, etc. I would leave the sensor in place in order for it to determine maximum ET.

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