Rainfall is free irrigation, but not all rainfall in your garden is usable. If you are not measuring and using the rain properly for irrigation, you could be wasting a valuable free asset for your garden. It does not matter if you manage 1000 acres, a small home garden, or an HOA’s landscape. Understanding these four concepts will help you be a better water manager.
How Much Rain Is A Heavy Rain?
Rainfall in your garden is typically described as light, moderate or heavy, but how much waterfalls with these descriptions. Light rainfall is considered less than .10 inches of rain per hour. Moderate rainfall is defined as .10 to .30 inches per hour. Heavy rainfall is more than .30 inches per hour. These descriptions provide two factors, how much rain over a period of time (one hour). This is essential information to know, but this information alone is not enough information to decide how much to water.
Understand The Concept Of Effective Precipitation
EP is the amount of rain added and stored in the soil. If your soil is dry and you experience light rain, most of the rain will evaporate from the soil’s surface and not be used by your plants. Conversely, if you have clay soil and experience a heavy downpour of an inch in a couple of hours, your soil will not be able to soak up the rain, and the majority will run off, wasted.
Know The Infiltration Rates Of Your Soil
Understanding your soil type (Here is a link on how to do a soil test) is the first key to knowing your infiltration rate. Infiltration rates are helpful because they help identify how much of the rain will be usable. If it rains more than can infiltrate your soil, it will be wasted. Rain much less than what your soil can accept will evaporate and not be used by your plants.
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Soil Texture |
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Sandy |
Loam |
Clay |
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Water Infiltration Rate (Inches per Hour) |
2 – 6 |
0.6 – 2 |
0.2 – 0.6 |
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Amount Of Water Needed To Wet A Dry Soil to 12” |
1” |
1. – 2” |
2.5” |
How Wet Is Your Soil When It Rains
The final factor for getting the most benefit from rainfall is how wet is your soil when it rains. If you watered the day before it rains, most of the rain would be wasted. If you water a normal amount the day after moderate or heavy rain, most of the irrigation will be wasted as well.
Use A Smart Controller That Uses Rainfall In Your Garden For Irrigation Scheduling
Purchasing a smart controller like the ETwater controller using Jain Unity makes all these calculations easy because the controller does it all for you. Jain Unity measures rainfall, calculates the effective precipitation based on your soil type, knows your current soil moisture balance looks forward to rain events and automatically adjusts your irrigation schedule. These calculations are done on an hourly basis, so you get the most benefit from rain.
https://www.youtube.com/watch?v=0CddX_gEIYY