Understanding Plant Hardiness and the Growing Season

Do you know which plants have the best chance of surviving the winter? How about which fruits and veggies will provide their full bounty before the growing season ends? All of this and more can be determined by 3 important pieces of information and a little sleuthing. Read on to see how!

What are USDA Hardiness Zones?

The USDA Plant Hardiness Zone Map assigns any given area in the United States one of 13 hardiness zones, based on the annual minimum winter temperatures over a long period of time and divided into (roughly, on average, mostly) 10-degree Fahrenheit bands across the country. It progresses from cold to warm, with Zone 1 being the coldest and Zone 13 the hottest, and has been expanded several times as more precise climate information becomes available.

This map is produced by the U.S. Department of Agriculture (USDA) Agricultural Research Service, and has an almost 100-year history, dating back to maps produced by the Arnold Arboretum in the early 1900s. Our current plant hardiness zone map, most recently updated in 2012 and spanning over 30 years of climate statistics, used to include Canada and Mexico, but is now exclusively for the United States (while Canada, Mexico and many other countries have their own maps, based on their own climate data)

When is this useful?

The hardiness of plants (chiefly perennials expected to stand the test of time, including many landscaping elements such as shrubs and trees) is largely measured by how well they can withstand the cold winter.

Many plants come with a hardiness zone suggestion on the label, indicating which plants have the highest chance of successfully surviving the winter in your climate. Hardiness zones are less of a consideration for annuals and other plants which complete their life cycle (seed sprouting to seed producing) in a single year. Annual flowers such as petunias and veggies like zucchini are great examples, and you might see these plants given a zone rating of 0 to indicate they aren’t hardy anywhere. Again, that doesn’t mean that they won’t grow, just that they won’t survive the winter.

Not the whole story

As mentioned above, hardiness zones are much more useful in predicting the survival of perennial plants than they are of annuals, because annuals will die off for the year regardless of temperature extremes. In between these two types of plants are outliers known as “tender perennials”. Tomatoes, for instance, are an annual up to zone 10, but perennial in warmer tropical regions such as Florida (zone 11a-11b), Hawaii (zone 12) and Puerto Rico (zone 12b/13a)

Zone information alone is often not adequate for predicting winter survival, since factors such as frost dates and frequency of snow cover can vary widely between regions. With that in mind, if you’re planting tropical citrus (suitable for zones 10-13, where the temperature never drops below 30 degrees) in the upper midwest (zones 3-4, where temperatures can reach -40 degrees) you understand it to be a risky venture.

Find your Plant Hardiness Zone by Zipcode Here

Frost Dates, Days to Maturity, and You

As a gardener, there are two frost dates that matter: The last frost in spring, after which plants can be safely planted, and the first frost in fall, when your flowers and vegetables will start dying off and no longer be producing. Between these two days is your area’s growing season.

We use the days between last and first frost dates to know how long our growing season is—count the days between the dates, and that is how long you have for growing different types of plants. You’ll want to make sure you have enough time for the plant to get to the harvest point (days to harvest) before you get to this first frost date.

While there are plenty of estimates for the last and first frost dates of the year, such as the farmer’s almanac, local resources and word of mouth from seasoned gardeners in your area are likely your best bet if you want more precision than a geographical average can give you.

Most crops need a growing season of at least 90 days. The length of your growing season depends on where you live (in tropical regions where it’s warm all year round, for instance, the growing season can last the entire year) and in general the colder the climate, the more important it is to pay attention to the “days to maturity” range and choose shorter-season crops.

Making the Most of Your Growing Season

The “Days to maturity” estimate on fruits and vegetables is a little misleading, since it refers less to when the seed first started to sprout, and more to when the seedling (having produced at least 1 set of true leaves that can photosynthesize) goes into the dirt outside. Some of us *ahem* may remember being bitterly disappointed not to have a robust radish crop 22 days after planting, but that’s not taking into account the time (generally 6-12 weeks, although like everything else, it varies) for the seedlings to reach that point.

Starting seeds indoors, then, is especially important in shorter growing seasons. Just keep in mind that that first 6-12 weeks of growing doesn’t really shorten your days to harvest as much as they keep it from being extended longer and later into the year.

Putting it All Together

For perennials, including most plants used in landscaping, consider the hardiness zone a very strong indication of your plants’ long term health and chance of survival and make your selections accordingly.

For annuals and tender perennials, use your frost dates to determine the length of the growing season in your area. This will help you understand when and what to plant for maximum beauty and an ideal harvest.

When starting seeds, add around 2-3 months to the days to harvest duration to account for the transition from seed to plant.

Use these 3 pieces of information to make the most out of your garden or landscape and enjoy amazing results year after year, and remember that Newberg Landscaping Pros is here to help you get the most out of your garden, yard or landscaping project. Give us a call today and see what we can create together.