Monthly Archives: September 2012

Winter Chill for Fruit Trees in Southeast Texas 1992-2012

The attached pdf table below summarizes the accumulated chill units at every National Weather Service Weather Station in Southeast Texas between fall 1992 and fall 2012 that reported 10 or more years’ data. What the table makes clear is that all areas experience a very wide range of chilling unit accumulations from one year to the next with the last five years being a textbook case of this. The winter of 2012 was in most places the lowest chill in the last 20 years, while 2009 was one of the coldest.

In the low chill areas, fruit growers should  plant trees requiring very low chill because late frosts are very rare and the plants will fail to thrive if they get too little chill. In areas of medium high and higher chill, the dangers of late freezes are strong, so in some areas it may be best to pick trees with chill toward the center of what is possible.

The attached table lists chill unit accumulation (what once was called chill hours) by percentages of time the winter in the last 20 years had the chill listed in column headers.

Southeast Texas Chill Unit Ranges 1992-2012

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Annual Winter Low Temperatures in Southeast Texas 1992-2012

The attached table in PDF  represents a concise summary of annual low winter temperatures (October to April) for all official national weather stations in Southeast Texas for which there is 10 or more years of data since 1992. Most of them are for the full 20 years of data. The table lists weather stations first by Houston area locations (Harris County), followed by other sites in coastal and near-coastal counties bordering these (that is 0 and 1 county from the Gulf).

After this are other “interior” counties in Southeast Texas.  For these, there are 2 or 3 counties that must be passed through to get to the coast. “County numbers to the coast” is a rough proxy for distance from the Gulf, and in rural areas is a very rough approximation of winter temperatures. The warmest areas generally are within a few miles of the Coast, and with some significant warmer exceptions for dense urban areas and Galveston Bay, temps get colder as you go inland. Lastly there is a a table of selected sites north or west of Southeast Texas.  These are included to help interpret information about fruit tree performance in those areas, in order to use such information in Southeast Texas. For example, avocados that do well in Devine, Texas will likely do well in College Station south, because temperatures south of College Station are warmer than Devine, while north of College Station are typically colder, so would need increased protections.

The numbers in the cells represent temperatures F. If for example a cell has a temperature of say 28 in a column labeled 30% (as it does for Intercontinental Bush Airport), this means that 30% of the annual winter lowest temperatures during the last 20 years were at or above 28˚F.  If you are considering planting a fruit tree that needs temperatures above 25˚(like a mango) , you can use this information, plus a comparison between your site and the nearest National Weather Station’s temperatures, to determine how much freeze protection a mango (or any other tropical or semi-tropical) would require.

Southeast Texas Winter Low Temps 1992-2012

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