Lisa's Landscape & Design

Saving the Planet One Yard at a Time

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

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 temperatures but they may not do well in our number of cold hours 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.

The four main criteria are cold or chill hours, heat tolerance, environmental location and annual average rainfall. The chill hours (hours between 32 and 45 degrees F) are extremely 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) and you live in an area (like us Austinites do) 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, like Dallas for example, and you plant one intended for low chill hours like we get here in Austin, it will result in its fruiting prematurely and you will lose your fruit to frost. Chill hours are the required number of cold hours in a season for the tree to produce fruit. If you plant a tree that requires more chill hours than you get in a season, you may end up with no fruit at all. 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. 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. Finally, there is the annual rainfall map and that will tell us approximately how many inches of rain we can expect annually. 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. Here is the first place to start…

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 your 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 should be marked Zone 8A/8B and this means that plant can survive in temperatures as low as 10-20 degrees F.

hardiness zone map

Plant Hardiness Zones

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 and as mentioned above, when choosing fruit trees it is really important to consider this when making your choices. 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, you should be able to locate one on Google images.)  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, it really does get too darn cold for them to survive the Winter (as most people in my neighborhood who had huge palm trees installed found out during the bad freeze we had two years ago). 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 precipitation map is also an important consideration when choosing plants for your region. This map is based on the average rainfalls over the past 40 years or so (although we have gotten less and less rainfall over the past several years). Choosing a plant that requires more water than your area will receive can only mean that you will have to use supplemental water on the selected plant or plants which sounds like a lot of work and wasted time to me. 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 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 rain water over tap water any day!

Precipitation map for Texas

Precipitation map for Texas

The next cool and colorful map I will share with you 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, its 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

Eco Region Map

Last, but not least is the heat map and this is important only because…really I have no idea why this is important to you as it is to the people who determine what plant does well in what zone and frankly, now that I think about it,  I just find this one depressing. Who wants to be reminded that we live in a city that is hot as hell most of the Summer and the amount of days over the temperature of unreasonably hot is too many?

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

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

While the only map I could find is rather tiny, (Freudian perhaps?) the sad truth is that we get between 120 and 150 days over 86 degrees. What that means to the Austin Texas gardener is that is really freakin’ hot and it seems to be getting hotter every year. In fact, I enjoy my gardens from my windows during the Summer time and I find it more and more difficult to stay out past late morning without feeling miserable outside. 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 time, when the heat is on I am done and I need plants and trees that can hang with the heat when I cannot.

So now that 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 may have cut out for you. Do your research on the types of plant that are recommended for your zone and collect water in rain barrels. 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”

Check me out on YouTube!

1 Comment

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