Austin Hardiness Zones, Precipitation, Environment and Yeah, it’s Really Hot Here!

Lisa's Landscape & Design ♦ 01/12/2013 ♦ 1 Comment

When trying to decide what plant to choose, you first have to consider where you are planting. Not only the location in your yard but the location in your state. I am in Austin, Texas and we are in Zone 8a/8b- ish. This is an important distinction because certain plants will do well in our average temperatures but they may not do well in our number of cold hours, extreme heat or lack of rainfall. There are a number of considerations when Zone 8A/B plants are selected and recommended by the experts and they need to fit all of this criteria.

Chill Hours

The chill hours (hours between 32 and 45°F) are important to consider when you are planting fruit trees for example. If you choose a high chill hour fruit tree (like one that would do well in Dallas with nearly 1000 chill hours) but you live in Austin that may only receive 400-600 chill hours, you may end up with no fruit at all. If you are in a zone where you get a higher number of chill hours and you plant one intended for low chill hours, it will result in its fruiting prematurely and you will lose your fruit to the next frost. 

I had a hard time locating a decent Chill hour map, so I will cheat and just tell you that those of you in Austin get between 400-600 chill hours, if you are further north of Austin you get between 600-800 and further south, it is from 200-400 which is where your citrus will do better. (If you are elsewhere in the country, locate a chill hour map for your area online.

Trying to grow tropical plants and citrus in Austin is tricky because while we do have the right humidity and heat to grow a lot of tropical and citrus plants but just because it will grow here, does not mean it will survive our extreme cold snaps. If you plant citrus you are best to leave them in pots or plant them on a Southern protected side of the house, or keep your frost cloths handy.

The Right Hardiness Zone

The Plant Hardiness Zone Map is one of the first things you want to familiarize yourself with. Knowing the zone you’re in is really important when choosing the right plants. This map is a minimum temperature map that shows the record lows and/or typical Winter temperatures that we would expect in any region in the US. The plants we use here in Austin should be marked Zone 8A/8B and this means that a plant can survive in temperatures as low as 10-20°F and as hot as 115°F.

Plant Hardiness Zones

Precipitation

Average Annual Rainfall

The annual rainfall map will tell us approximately how many inches of rain we can expect each year. Choosing an expensive tree that prefers to have wet feet in a climate that gets very little rainfall can be a financial disaster in the making. Here are the maps that you can refer to when making your plant choices. If you are new to this area, you will find that this information is really valuable. If you have lived here for some time and are not having success, it may also be of help as you might be using plants that do not belong here.

This map is based on the average rainfalls over the past 40 years or so. Choosing a plant that requires more water than your area will receive can mean that you will have to use supplemental water on the selected plant or plants which is water we don’t have. Besides, why bother with a plant that’s a water hog when we have perfectly good plants that aren’t so darn thirsty!

This map also tells all of us we need rain barrels because a couple of feet of rain a year is not much considering how many people are using the aquifers and how little rainfall we have to replenish our lakes and streams. The average 2000 sq foot roof can collect up to 30,000 gallons of water so why not catch it and keep it! Free is free all day, and your plants will take rainwater over tap water any day!

Precipitation map for Texas

The Soil You Have 

The Eco Region Map tells us if we are in hard clay or fertile soil and that may be a huge factor for the success of the plant you choose. Planting something that needs well drained soil into a rock and clay bed will be a task of futility.

The next map I is the environmental map and I love this one because it shows just how incredibly diverse this big-ass state really is. We have some of the most interesting contradictions from desert to marshlands, to ocean to mountains and somewhere in between. The geology of Texas is fascinating and if you have not done your homework on the geological history of Texas, I encourage you to do so, it’s pretty awesome. This information is important because it is helpful to know your ecological region as it will help determine your soil, plant choices and amendment issues.

Eco Region Map

Heat Index

The heat index is valuable information because it can tell you whether a plant is meant for a shady afternoon spot instead of our burning hot afternoon sun.

Heat Zone Map-Guess what? It’s hot here!

While the only map I could find is rather tiny, the sad truth is that we get between 120 and 150 days over 86 degrees and over the past many years we’ve had dozens of days over 100. What that means to the Austin gardener is that it is really hot and it seems to be getting hotter every year. For that reason my plants need to be super heat-hardy and super low water and low maintenance because while I am a garden-oholic in the spring, I need plants and trees that can hang with the heat when I cannot. The Austin heat index is a “feels like” number. This means that even though it is 105° outside, it may feel like 115 in the sun. Your plants need to be able to recover over night or they will not make it through the summer. 

Once you have a better idea what type of climate you live in, you can make better choices about the type of garden you want to grow and the amount of work you have ahead of you. Be sure to heed the suggestions when it comes to the amount of sun a plant can take and the amount of water a plant will require, and you will be well on your way to an awesome, climate happy garden.

Now go get your “climate appropriate” garden on!

Lisa LaPaso

Lisa’s Landscape & Design ( “like” me on facebook)

“Saving the Planet One Yard at a Time”

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