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Randall Chill and Cold Zones for Southeast Texas

This 3 page file has my 2012 Winter Hardiness Zones for annual low temperature 1992-2012 in all National Weather Service Weather Stations with 10 years of data. The winter low temperature zones differ from USDA because the lows I am using are for the winter, not the calendar year. The way NWS reports things, a very cold last week in December and a very cold next week in January are treated as two different annual lows. Since we tend to swing from El Nino to La Nina events, this leads to very misleading data. As well, my tables use the last 20 years, rather than the 1975-2005 that the 2012 USDA model uses.  Since 1975-1990 had some of the coldest days and months ever in the Houston area, this is not very helpful.  As well, I take median average low temperatures at smaller intervals than 5-10 degrees. There is a big difference in fruit tree tolerances for mangoes between 28F and 25F.  Lastly, I list chill zones for the area. These are not quite the same as the low temperatures since they are based on cool temperature duration more than a specific cold night.  The last page is the USDA current zone map which is quite at odds with my data.

Randall Southeast Texas Low Temperature Zones

Native Plants in the Year Round Food Garden

In October, I gave a talk at The Houston Arboretum and Nature Center to The Native Plant Society of Houston regarding what I saw as the role of native plants in the Year Round Food Garden.  The pdf is below

Native Plants & the Food Garden 1018

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

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

Weird Weather

201004 Weird Weather

Permaculture Guilds in Houston

One important aspect of permaculture design is the effort to place things so they benefit each other.

Permaculture Guilds

Use Nature and Permaculture Stacking to Increase Yields

In the classes I teach, home owners who have become aware of the thousands of possible vegetables, fruits and herbs they could grow, often lament “I just don’t have any more space for that.” 

As a possible solution, they usually ask me what will grow in shade, and I usually tell them that many herbs, vegetables where you eat the leaves, and blackberries are the best possibilities. But that brief answer is simplistic.

What I would say if I had time to explain is that, “Permaculturists have a technique called stacking that may help you.” Stacking is useful in situations where you think there isn’t enough land for your goals, and you want to get more out of less.

Permaculture is a design philosophy and methodology. It integrates ancient and modern technologies with an understanding of nature and detailed observation, to guide effective plans for sustainable living. It is taught in 72-hour classes in periods from ten days to a year.

In aged natural forests, there is a tall tree canopy layer fifty feet or more above the earth, with shorter, more shade tolerant trees below them, and even more shade tolerant low-growing bushes, shrubs, herbaceous plants, ferns, and fungus living close to a heavy mulch layer and the earth itself. On the trees, there are often vines such as wild grapes, Virginia creeper, or cross vine.

These forests contain many times the biomass of a similar acre of less layered vegetation such as prairie, most gardens, lawn, or edged walkways.  So per square foot they produce much more soil-building plant liter.  That in turn, prevents runoff and holds much more moisture for much longer.

The shade canopy acts like a 50 ft. insulation, keeping temperatures cooler, so there is much less evaporation from the surface. The mulch layer also keeps the surface damp even in summer, so the roots, mainly near the surface have a continual supply of moisture to support growth.

The tree layer provides millions of square feet of leaves whose water content keeps them from cooling or heating as fast as the surrounding air. So dew condenses on them, producing more precipitation. The plants then use a high portion of the water collected, and eventually transpire it back into the air.

Worldwide, 60% of all rainfall is from plant transpiration. Inland the percentages are higher and near the ocean lower.  Thus Galveston rain is mainly from the ocean, but Houston tap water, coming as it does from the Trinity, is mainly of botanical origin. So natural forests and woody landscapes are not just the lungs of the planet, but also its blood supply! Native understory plants like ferns, beautyberry, scarlet buckeye, and parsley hawthorn do a lot of good for us.

Another natural design found in forests is the guild. This is an assemblage of plants, animals and other items that provide benefits for each other, thus making it possible for more to live in a smaller space. For example, a blackberry thicket might protect a young tree from deer, and later, the older tree might provide mulch and bird droppings to help the blackberry grow.

A third natural design we can use in our gardens is ecological succession. If a forest is partially cleared by an avalanche, disease, or fire, new sun-loving plants occupy the cleared ground quickly.  These provide shade and organic matter to nurse small shrubs and trees, and these in turn help even taller trees to emerge.

Thus without any human help, nature has sustained itself here for millions of years because it has a very efficient system for growing plants close together. But we too can use natural and other designs to stack our yards.

Stacking is related to understory, guild and succession, but embellishes these designs for the purposes of gardening. Vertical stacking is an effort to plant several useful plants of different heights in the same space.

In horizontal stacking, by contrast, several useful plants are planted adjacent to each other in order to benefit each other This is done using the guild concept—beneficial assemblages promote higher production.

Temporal stacking places plants near each other that will enjoy most of their growth during different seasons, or years.

In my own garden, I use stacking to squeeze more and more production out of my house-lot. I grow several sweet varieties of hybrid muscadine grapes on a wire between ten-foot U-stakes. Vertically stacked below these are domestic blackberries tied to the stakes. And below them on the ground suppressing weeds is our favorite summer green– sweet potato spinach.  These three plants all do well in sun, but two are still productive in partial shade, so we can make use of this to vertically stack.

Horizontal stacking uses mutually beneficial qualities of plants such as the different micro-climates created by different plant heights. In winter, the warmest part of my yard is on the southwest side of my house in a sunny space between two tall grapefruit trees. That’s where I have my tropical plants—papayas, guavas, pentas, tropical passionfruit and two coffee plants. There is no room for more grapefruit but plenty for these heat loving smaller plants.

The typical temporal stacking is to understory a preferred tree that when it gets big enough, can replace what was above it. I am growing a very hardy experimental avocado under a poor quality citrus. But a less obvious example is the strawberry patch.  Strawberries need winter sun to produce and summer shade to be perennial.  The solution is to leave two-foot wide spaces in the strawberry patch so that summer vegetable plants such as basil, peppers and okra can be planted where they will shade the strawberries all summer.

Stacking is just one of more than two-dozen sustainable land design concepts to be taught in permaculture classes through Urban Harvest at


Shifting to Local Food

Shifting to Local Food

In September 2008, Gary Edmondson and I presented the above to a Houston Tomorrow HGAC Conference on improving the Houston Food Supply.