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Our Experts Answer Questions, Share Resources

Updated on Dec 20, 2024
By John Lenz

Hardiness Zones? Days to Maturity? A few of our experts’ go-to resources 

Fielding customer questions is one of our favorite things at Baker Creek. It’s rewarding to know that people trust us to help them become better gardeners. But when the experts have questions, where do they go for answers? Here are a few of our go-to resources and answers to some of the most asked questions. 

What is the hardiness zone map and what does it mean?

The history of the USDA Plant Hardiness Zone map goes back to 1927, when Dr. Alfred Rehder of the Arnold Arboretum at Harvard compiled data from a survey of plants and their survivability in different parts of the country. The map was first published in his Manual of Cultivated Trees and Shrubs. Others built on Rehder’s work, including Dr. Donald Wyman, who in 1938 used 40 years of National Weather Service data to build a map. 

Black & white map of US with Climate Zones I-VIII indicatedDr. Rehder's zone map was first published in his 1927 book Manual of Cultivated Trees and Shrubs.

The USDA published its first hardiness map in 1960, using data from 450 weather stations around the country, but the Arnold Arboretum map remained the predominant resource until 1990, when the USDA updated its map with data from thousands of weather stations. 

The map has been updated three times since its publication; the last update, in 2023, shifted about half the country into new zones. 

2023 USDA Plant Hardiness Zone Map 

While it is the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location, the hardiness map does have its limitations. It is based on the average annual extreme minimum winter temperature. Please note that the hardiness map applies only to perennial plants -- not annuals. About 90 percent of our variety offerings are grown as annuals. We provide relevant zone information whenever possible, and recommend using your local frost/freeze dates to plan your garden and determine the best times for starting and planting your seeds. 

Colorful map shows the latest revision of the USDA's hardiness zonesThe USDA offers an interactive map where you can look up your planting zone by zip code

When will we get the first frost and the last frost of the season?

The difference between the average last frost date in the spring and the date of first frost in the fall is the number of growing days in your season. This may tell you if a certain crop has time to mature and help you decide when to plant. The National Gardening Association offers this handy web tool that allows you to look up your average frost dates by zip code

What’s more important in gardening – soil temperature or air temperature?

Next to moisture, soil temperature is the most important factor determining whether a seed will germinate. Cool-season crops can germinate in soil temps as low as 40 degrees F. Warm-season crops need the soil to be at 60 F and above to germinate, while some warm-season crops prefer the soil to be at 75 F or warmer. Air temperature is not really a factor unless it drops below 35 F or gets hotter than 95 F. Below 35, you risk frost damage and above 95, flowers and fruit can abort. You don’t need a fancy soil temperature probe; a kitchen meat thermometer will do. Just make sure that it will register temperatures to 32 F or below. To take your soil’s temperature, push the thermometer probe four inches into the ground. 

tiny, bright green seedlings in tray of dirtWatermelon seeds need warm soil to germinate

What goes into determining Days to Maturity (DTM)?

DTM refers to the number of days from planting the seed until the first fruit is harvested. The problem with this number is that it can be affected by soil conditions, weather conditions, fertility, light conditions, and other factors. DTM varies quite a bit from Alaska to Oregon to Southern California. It's only good for a rough estimate, based on observational data under optimal conditions. Your results may vary.  

Day length is another important factor in days to maturity; it refers to the number of hours of light in a 24-hour period. Most plants stop growing when exposed to fewer than 10 hours of light per day. Day length is correlated with latitude, and it changes more in higher latitudes than lower ones. (At the equator, day length is always about 12 hours.)  

To determine your ideal planting date, we recommend subtracting the days to maturity from the average first frost date, adding 1 to 2 weeks to account for slower growth after the summer solstice. Calculating day length is as simple as plugging in your location data to a tool such as the Old Farmer’s Almanac Sunrise and Sunset lookup

hand holding a bunch of orange carrots freshly pulled out of the soilMany factors determine the number of days from planting to maturity

Where can I find reliable gardening information for my area?

There is no single greater resource for gardeners than their local cooperative extension office. Every county in the U.S. has one. 

The Smith-Lever Act established the Agricultural Cooperative Extension Service in 1914, but the roots of extension go back to the agricultural clubs and societies of the early 1800s. The Extension Service is associated with land grant institutions (colleges and universities) in all 50 states, the District of Columbia, Puerto Rico, Guam, the U.S. Virgin Islands, American Samoa, and the Northern Mariana Islands. County or regional extension offices exist to share knowledge from agricultural research and meet the specific needs of the communities they serve. To find your county extension office, visit the Extension Foundation’s directory of state cooperative extension offices and search for your county or region. 

For even more detailed information, we compiled a list of cooperative extension planting guides in all 50 states. The interactive map at the link will take you directly to each state’s guide, where you will find a wealth of information. 

green background with blue US map. States outlined in white.Click on the map to find local planting guides for all 50 states!

Soil Health and Plant Nutrition:

Montana State University has a particularly good guide to plant nutrition, with easy-to-use visual diagnostic tools: 

Nutrient Deficiencies - MSU Extension Soil Fertility | Montana State University

What’s Wrong with My Plant?

The University of Minnesota developed “What’s Wrong with My Plant?” It’s a web app that allows users to drill down from crop type (beets, legumes, cole crops, etc.) to symptoms and offers visuals and likely culprits for the problem. The U of M Extension also offers diagnostic tools for ‘is this a weed?’ and ‘what insect is this?’ Diagnose a problem : Garden : University of Minnesota Extension

hand holding unhealthy-looking tomato branchMany plant diseases are easy to combat with good information!

Plant Disease Guides:

There are many resources for understanding plant diseases and pests, but we regularly find ourselves consulting these: 

The College of Agricultural Science at Oregon State University developed a Plant Disease Guide to the Pacific Northwest, in conjunction with Extension bureaus in Washington and Idaho. 

The Extension Service of Texas A&M University developed a stellar plant disease handbook, which includes an extensive section on food crops

Finally, check out our handy clickable map of plant disease and pest resources by state!

Seed Saving:

Good information about seed saving is also readily available. For example, The University of Minnesota’s Extension Service Guide is concise and easy to follow.  

Seed Savers Exchange, a nonprofit devoted to the preservation of heirloom varieties, also offers a wealth of information about seed saving: Seed Saving - SeedSavers

About the Author:

Bearded man in brown cap carries an armload of large cabbagesHorticulturist John Lenz in the garden

Visitors to Baker Creek’s Mansfield, MO, seed store may know John Lenz as an affable and loquacious storekeeper, but he is also a horticulture expert who oversaw our greenhouse program during a time of rapid expansion. He has a degree in horticulture from New Mexico State University and an MBA from St. Leo University in Florida.  Stop in and say hello if you are visiting our Mansfield, MO, location! 

You can always email your gardening questions to seeds@rareseeds.com. Put "hort question" in the subject line, and John or someone else on the horticulture team will get back to you.