When to Plant: Part 1. Figuring out Your USDA Plant Hardiness Zone

Uncategorized Jan 24, 2020

New gardeners are often unsure when to plant. 

I wish I could tell you an absolute answer, but it's not that concrete. 

But don't worry - it's not difficult to figure out, and plants can be very forgiving. In other words, if you plant a week later or earlier than the "ideal" date, you're probably OK. 

<hack>The easiest way is to ask a nearby gardener! Watch your fellow community gardeners and see when the majority of them are planting. Or ask at a local high-quality garden center. </hack>

But, I'm writing for a nation-wide audience (maybe even a global audience!) so I'll explain how to figure out when to plant anywhere in the United States.

To keep these articles from getting too long, I'll explain it in a few articles over the next few days, then wrap it up in a summary post.

What's Your Zone?

In the United States, the Department of Agriculture has developed the concept of "zones" across the country. Here's a map with the zones imposed on it:

Zones are a way to generalize the climate across the country. Each zone is indicated by the same color on the map above. For example, all of the areas colored in with the dark blue color are in Zone 4b.

Within a zone, the climate is very similar. For example, the climate in Kansas City is roughly the same as the climate in southern Indiana.

Adjacent zones have similar climates, but not identical. For example, the climate in southern Georgia is similar to central Georgia's climate, but a bit warmer. 

Make sense?

I'll show you how to use the zones to figure out when you should plant using the example of my own garden, here in Overland Park, KS.

Step 1: Find Your Location On A Zone Map

Find your city/town/village on the map. 

Pretty simple. 

See below for Overland Park, KS. 

Yep, right there in the middle.

Step 2: Which Zone Is It?

Look at the color. Then look over to the color legend and match the color. That's your Zone. 

Overland Park falls in the dark green color, which we see is Zone 6a. See below.

Truth be told, you can get super-detailed on your Zone if you want to. In practice, just knowing the Zone number (i.e. Zone 6) is good enough.

Here's a link to an interactive USDA Plant Hardiness Zone map.

Congratulations!  Now you know your Zone! You will need this for the next step.

Good news - you never have to learn it again... unless you move to another part of the country. 

(or if the climate changes, but that's a discussion for another time)

Step 2a: Significance of Zones

(Read on if you want to geek-out on zones a little!)

Zones are determined by historical data by averaging high and low temperatures throughout the year. Depending on which data were used, the maps might be slightly different. 

I just determined that Overland Park is in Zone 6b. But when I enter my ZIP code in the Interactive Map, it tells me Zone 6a. Not really a huge difference for most situations.  

Temperature is influenced by physical features of the land. These include:

Location on the Earth - how far north or how far south. This determines how much sunlight the location gets throughout the year. More sunlight = warmer.

Elevation - the higher up, the cooler it tends to be. The lower, the warmer. 

Proximity to a large body of water, like an ocean or large lake.

It boils down to this - when you know your Zone, you have a good idea when it warms up enough to plant your garden, and when it becomes too cold and it will freeze and kill your plants. 


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