Drip Flow Rate --- Here’s some drip info for you. The rate at which water comes out (flow rate) of drip depends on the product used but can range from .2 gallons per hour (gph) to 1 full gallon per hour. That rate is per each emitter (hole) in the tubing. [Note: 1000’ of drip tubing may have 56 – 83 emitters.] Just hold on to that thought for a minute.
Soil --- Our lovely north Texas clay/loam soil is called Blackland Prairie soil, (fact checking url http://en.wikipedia.org/wiki/Texas_blackland_prairies). This silicate based soil has very tiny capillaries which means water has fewer spaces to move through in this soil, but it still moves in multiple directions (up, down, sideways …wherever there are capillaries). Translation, since this soil is so densely packed, water moves through it slowly and tends to remain for a long time (hours to days depending on surrounding plant material, slope, seasonal temperatures, sun vs. shade, etc.).
Field Capacity Absorption --- Our clay soil can only absorb (infiltration rate) about ½ an inch of water in an hour. After that amount of water is absorbed into the top layer of soil, the soil is essentially full and any additional water we try to apply simply runs off, (like a glass that is full, it too can’t hold any more water).
Drip Product --- Drip tubing is available from several manufacturers. It is also available with different head spacing – drip tubing is hollow flexible tubing with a hole (emitter) every 6”, 12”, 18” or 24” apart. Each “hole” actually has an emitter behind it inside the tubing and that emitter delivers a regulated drip at a regulated speed – that becomes the precipitation rate or gallons per hour (gph). Typically, the irrigator will determine the best drip product for your needs – we generally prefer 12” spacing with .6gph tubing – we found this drip to perform best in clay/loam (we sometimes suggest 18” spacing for slopes and parkways). Remember that 1000’ length, at 12” spacing there are 83 emitters, 18” spacing has 56 emitters.
How Long to Run --- So, now we need to translate the gph into inches per hour. Suggested drip rate is .6 gph which delivers about ½” of water per hour. We can now figure out how long to run the drip. Drip applies the water evenly and slowly and fills the soil in approximately 15-40 minutes (depending on above mentioned conditions).
You’ll need to make sure the drip runs correctly throughout the year to keep your plants healthy and foundation managed correctly. This means understanding scheduling to consider the seasonal conditions, etc.
Back to the frustrating math…running .6 gph drip for longer than a ½ hour will definitely cause run-off and simply waste water. Granted it is a slow application rate, but beyond 30 minutes is too much water to be absorbed by our soil in 1 giant run time. Breaking down the run time into 15-20 minute run times is the first part of managing drip. You now know how long to run a .6 gph drip station.
How Often to Run --- The second part of managing drip is how often to run it. This takes some understanding of how drip is supposed to work. Drip is supposed to keep the soil evenly moist. You don’t want the drip to dry out because drip cannot “catch up” and re-saturate the soil after a dry-out period, the soil will need to be wetted from above (hose) then drip can maintain the moisture level through normal scheduling.
That said, the “how often” (# of days a week) becomes crucial to effectively keeping the soil moist. – Remember drip is exempt from most watering restrictions not only because it is a regulated slow application rate but also because it needs to run multiple times a week to work properly and effectively.
Usually, a daily dose of drip in the hot months will suffice to keep the soil moist and the drip effective (5 or 6 days a week watering). Then when our season changes, adjust how often drip runs during cooler temperatures. When temps are 70˚ or less (average daytime temps) run drip every other day (3-4 days a week). When temps are 50˚ or less, try every 3 days (2-4 days a week). These are suggestions and a great starting point.
Wrap-Up --- Drip is 90% efficient, but only as effective as the programming manages. Of course you’ll have questions, you should. This information is, well, informative, but somewhat complex.
Hopefully, it inspired you check the settings on your controller!
Patty Sipe - Heads Up Sprinkler Co. - 2014