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This past summer, I spent a lot of time wandering through my local, big box chain garden center dreaming about which plants I wanted to get for my yard (I wanted all of them!!!).  It’s fun imagining.  Then I decided I was going to put in plants around the lamp post in my front yard, and suddenly the pressure was on.  Choosing plants as a beginner gets overwhelming very quickly.  Back at the garden center,  I started where every good gardener starts-the plant tags.  Immediately, I was overwhelmed with information, but one line in particular (usually towards the top of the tag) had me feeling like I was way out of my league.  You guessed it: zones.

So I started looking around the internet to see what’s the big deal.  And I now feel a little silly that I was intimidated by the terminology for as long as I was.  You guys, zones are merely temperature guides.  That’s it!  I thought it was some fancy, secret, expert-gardeners-only-newbs-need-not-apply thing that meant all sorts of growing science that mere mortals should never tinker with…  Not even close.  But as simple as the concept of zones is, there is background information that will make zones a bit more meaningful for you and help you have better success in plant selection.  And that’s what we’re covering today.  Cool!

 

What is a zone?  

You may have also heard/read the following terms: plant hardiness zone, growing zone, planting zone, frost zone…  In the gardening world, these all mean the exact same thing.  I usually just use the term ‘zone’.  However, ‘plant hardiness zone’ is sort of the official term for what we’re talking about. So let’s establish some definitions first.  

• Plant hardiness is the ability of a plant to withstand cold temperatures.  
• Plant hardiness zones is a classification system which shows the extreme cold temperatures that can happen in an area during an average winter (note that this doesn’t mean your cold temperatures are guaranteed to drop that low).  

For example, I live in a zone 4 which means an average winter for me can reach lows of -20 to -30 degrees fahrenheit (boo!).  

Someone living in Los Angeles, CA is living in a zone 10, meaning their winter low temps average 30 to 40 degrees fahrenheit (lucky ducks!).  

Note that plant hardiness zones do not directly reference the average annual highs in a zone.  While not necessarily the case 100% of the time, you can predict that if you’re in a higher zone where your winters are quite mild/hot, the summers there are going to have pretty high temperatures.

How are zones determined?

 

Hardiness zone temperatures are based on the annual extreme low averages from a 30 year period (more info here ).  Zones are divided by 10 degree fahrenheit increments.  Nice and tidy!  They are further broken down within each numbered zone by 5 degrees and denoted by ‘a’ and ‘b’.  In general, you’re ok to just stick to knowing your zone number.  You never know when you might come across a plant where that 5 degrees makes all the difference (plants tend to be a little less finicky than that though).  At the very least, it’s good to know what the ‘a’ and ‘b’ mean.

How do I find out what zone I live in?

The easiest and most convenient way to find out is the internet (so helpful, Alice!).  But really, if you live in the United States, the USDA website has a really handy map tool and where you can find your zone by typing in your zip code.  (They also have plenty more information about how they came up with the map in the first place.)  Or if you’re interested in learning about the zones across your state, you can search by that.  I personally think it’s interesting to see how much the zones can vary in my state alone.  It takes very little to thrill me.

If you’re stranded at your local garden center with no internet or cell service, you can also ask the lovely people working there.  They’ll definitely know, and they’ll probably be happy to tell you which plants do well in your area.

 

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How to Use Zone Information

Keep in mind: Hardiness zones assume that one will be planting outdoors directly into the ground.  Planting indoors or in a pot may alter the maintenance needs of the plant.  

Zone ranges

When looking at plant labels, it’s uncommon to see a plant labeled with one zone.  There’s usually some sort of range.  That simply means the plant is expected to be able to tolerate the temperatures in all of those zones.  

Perennials vs. annuals

Even if you’re a complete novice to the gardening world, at the very least, you’ve probably heard the terms ‘perennial’ and ‘annual’ in reference to plants.  And you’ve probably understood that perennials come back every year where annuals only last for one year.  While not entirely false, it’s not exactly true either…

A perennial is defined as a plant that can live beyond two growing seasons.  They can be shorter lived or last for a long time.  You were right about the annuals.  Good job!  And then there are also biennials which last for two growing seasons, but we won’t worry too much about them right now.  Cool!  So what do these have to do with hardiness zones?

Well, one factor in a perennial coming back every year is that it has to survive the winter.  Enter knowing your zone!

A few months ago, I came across a beautiful brugmansia in the plant building at my local university.  How cool would it be to plant that in my yard?!?  If you’ll remember, I live in a Zone 4.  A brugmansia is a Zone 9-11 plant, which means it will not survive in consistent temperatures below 20 degrees.  Does it mean I can’t plant it in my backyard?  No.  I can absolutely plant it.  But unless I intervene by digging it up and bringing it inside prior to my temperatures dropping, it will only last one growing season.  And this speaks to my next point…

A perennial in one zone can be treated as an annual in another.  Understanding this can give you some confidence to play around with higher zone plants in your garden knowing they are only meant to stick around temporarily.  Or maybe you can turn an annual into a perennial by creating ideal conditions for it indoors! 

Zones are a guide

Hardiness zone classifications were created as a guide to give you a better idea of what will thrive in your area.  Plants aren’t as rigid though, and there are a variety of factors that come into play when looking at the survivability of plants.  Temperature is just one of those.  

So let’s come back to me as an example.  In case you missed it, I live in a chilly Zone 4.  Let’s say I spot a beautiful perennial shrub that is labeled as Zone 5-8.  Don’t care, I’m going to plant it anyway!  I’m a rebel like that.  Does that mean it will for sure die on me during the winter?  Not necessarily.  Remember that hardiness zones are based on EXTREME averages.  So if I experience a warm winter that never dips below -20 degrees, that plant should come back the following year.

Now let’s say I have a day or two during the winter where it does dip below -20.  That’s not necessarily going to kill the plant either!  Where zones are set at 10 degree increments, plants are not.  There’s no mechanism where the plant  goes, “Whelp! Felt the temperature hit -20 degrees.  Time to die now!”  If those negative temperatures are sustained for a week or two, then perhaps I will prepare to have a dead plant come spring.  But in some cases, even that’s not a guarantee.  It is possible for plants to acclimate to colder temperatures than they were meant for.  

So that’s a long winded way to say, give fudging zones a chance!  As a rule of thumb, I wouldn’t exceed more than one zone up if you want the highest chance for success.  But if you’re feeling experimenty, go for it!  See what happens!

Future Planning

(Redundant, I know.)  Winter is a great time to start thinking about next spring.  One of my projects for the winter is to find some low maintenance plants to start filling my garden beds.  They’re not currently stocked at the local garden centers, but I can start researching on nursery sites.

 

 

And that’s about it!  I hope this demystified plant zones a bit for you.  It really is a great starting point as you start thinking about plants you’d like to use in your garden.  As always, let me know in the comments if you have any more questions about zones.  

P.S.  Did you catch that I live in a Zone 4?!?  What’s your zone?  🙂