May 31, 2014
1 - Networks of weather reporters can help you determine rainfall and need for irrigation in your garden.
Yard and Garden May 31, 2014
It rained in my area recently, but I do not think I received as much rain as reported on the news reports. How can I know how much rain I got and if I still need to irrigate my garden?
Rainfall in New Mexico can be very spotty. Isolated and scattered thunderstorms may be very isolated and very scattered. Some areas may receive much greater amounts of precipitation than locations less than a mile away. There are several online sources of information about precipitation that may be helpful. The National Weather Service, Weather Underground, and numerous other online sources can provide information about precipitation in your area, but the accuracy of that information depends on the distance to the reporting station. The Weather Underground web sites http://www.wunderground.com/ let you look at a map of reporting stations in your area to see if there is one or more near you. If you can find several near you, you can look for patterns of precipitation and get an even better idea of how much rain fell in your area. Another very useful site with numerous reporting stations is the CoCoRaHS (Community Cooperative Rain, Hail, and Snow) network http://www.cocorahs.org/. This is a network of volunteer weather reporters in the U.S. and Canada. There may be reporting stations near you from which you can draw daily precipitation information.
Of course the best way to know how much precipitation fell in your garden is to put a rain gauge in your garden. You will then have the most accurate information possible for your specific location. Not all rain gauges are equally accurate, so be sure to get a good one. If you choose to collect your own data, you may want to help your neighbors by joining one of the networks mentioned above. Digital weather stations often report to the Weather Underground network. Many of these also have web cameras showing outdoor conditions. The CoCoRaHS network works closely with the National Weather Service and has an online store selling rain gauges and other equipment. Reporting to one of these networks is a valuable service and an interesting activity. The maps on the CoCoRaHS site are interesting showing distribution of rain nationally and locally each day.
Finally to answer the question about whether or not irrigation is needed, even without a rain gauge you can check the depth of moist soil in your garden at a location does not receive regular irrigation to determine how deeply the soil was moistened by recent rains. This is a more critical measurement than the actual rainfall since the rate at which the rain fell as well as slope, soil compaction, and other factors determines how much water ran off and how much soaked into the soil. The quantity of water that soaked into the soil in your gardens determines whether or not you should irrigate. This determination is also dependent on the plants in your garden. I recently measured six tenths of an inch of precipitation in my garden in a three day period. When digging into the soil, I noticed that in unirrigated areas the soil was moistened to only 3 to four inches. In areas that had been irrigated were moist much more deeply. These irrigated areas can skip one or more irrigations. Watch the plants and the rate at which the soil dries to determine when you must irrigate again. There is a temptation to wait too long to begin irrigation as a means of conserving water, but when the plants begin to wilt irrigation must resume.
Deeply rooted trees and shrubs should remain on their previous irrigation schedule unless the rains moisten the soil to a depth of 2 to 3 feet, then one or more scheduled irrigation may be skipped. This may happen in areas where rain water accumulates after running off from other areas of the garden.
It is wise to conserve water when possible after significant rains, but it is also important to provide adequate water to your garden. Failure to provide adequate and timely irrigation defeats the purpose of gardening.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!