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okiedawn1

How to 'Know' When It Is Time To Water

15 years ago

We all know that very little recent moisture has fallen in recent weeks and months and that soil moisture levels continue to plummet.

So, how do you "know" when your soil is so dry that it must be watered? During the dormant season, there are not many green plants available to "wilt", which would provide one clue that moisture is needed. Sometimes it is hard to know if irrigation is "needed" or not, but I use the Oklahoma Mesonet's Fractional Water Index to help me keep an eye on soil moisture levels.

Every county has a mesonet station, and some counties have more than one. Mesonet Stations collect data literally minute to minute and the computerized results are always available and current.

For soil moisture, the mesonet uses the Fractional Water Index, an index that records moisture from 1.0 to 0.0, with 1.0 being totally saturated soil and 0.0 being totally dry soil.

You can view your Fractional Water Index at the link below, and can check the FWI at 5 cm (2"), 25 cm (4") and 60 cm (23").

If your FWI is from 0.8 to 1.0, you have excellent soil moisture and this gives you optimal environmental conditions for plant growth.

If your FWI is from 0.5 to 0.8, plants will be OK (surviving, but not thriving) but will have only limited growth unless you are giving them supplemental irrigation.

If your FWI is below 0.5, the soils are too dry to sustain plant growth. When the FWI is below 0.5, plant wilting is common, and so is eventual plant death. When the FWI is below 0.5, it is critical to irrigate your landscape unless water restrictions prevent you from doing so.

I always look at the FWI at all three depths so I'll know what the moisture levels are for all the plants in our landscape, whether they are shallow-rooted or deep-rooted. Currently, in Love County for example, the FWI at all three levels is very low--0.49 at 2", 0.34 at 4" and 0.07 at 24". Thus, I am running the sprinklers and soaker hoses a lot in the landscape around the house, and I still may lose some plants to the drought.

Of course, your soil likely is not exactly the same as the soil at your county's mesonet station or stations, but at least the mesonet data gives you a starting point. We are lucky to have this resource available to us as people in many other states do not have access to such detailed weather, climate and environmental info.

And, yes, you can check your soil the old-fashioned way, at least at the 2" and 4" levels, by sticking your finger down in the soil. : ) With my clay soil that tends to stay as hard as concrete in all areas where I haven't added compost to improve it, though, I'd break a finger trying to stick it down into the soil, so I rely on the mesonet data.

And, you might notice that some locations are at 0.0. Usually at that level, the soil is of a very, fine, almost flour-like texture because there just isn't any moisture to hold the soil particles together.

I just thought I'd mention the FWI because it is a great tool, and it is only one of the great tools the mesonet makes available to us, whether we are home gardeners or agricultural producers.

Once you click on the link below, you can click on the term "Soil Moisture" at the left side of the screen that says "Mesonet Data". You'll then get a map and a "Soil Moisture Levels" box in the upper right-hand corner of the screen, and at that box you can click on the three soil depths to see the corresponding numbers.

Dawn

Here is a link that might be useful: Oklahoma Mesonet

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