Hello, I’m Yun, the founder of The Planting Key. Welcome to the page that lies at the very heart of my mission.

You deserve to start your gardening journey with information you can trust. In a world of generic advice, I’m committed to being transparent about where my data comes from and how I process it. This page is my promise of accuracy to you. Here, I will pull back the curtain and show you the exact, meticulous process I use to create the planting calendars you see throughout this site.

The Core Concept: Everything Revolves Around Frost

For most gardens in North America (specifically, USDA Zones 4-9), the entire planting schedule is determined by two critical dates:

  • Average Last Spring Frost Date: The average date in spring when it is statistically safe from the last killing frost. Planting tender vegetables before this date is a major risk.
  • Average First Fall Frost Date: The average date in fall when the first killing frost is expected. This date signals the end of the growing season for warm-weather plants.

These two dates define your “frost-free growing season.” My job is to help you work forwards, backward, and within this window to maximize your garden’s potential.

My 3-Step Calculation Process

Every date in my calendars is the result of a simple but rigorous three-step process. I do not copy dates from other sources; I calculate each one to ensure internal consistency and accuracy based on my chosen methodology.

Step 1: Establishing a Baseline for Each USDA Zone

You may have noticed that even within a single USDA Zone, different towns can have slightly different frost dates due to microclimates. Creating a calendar for every single city is impossible.

Therefore, I use a “representative average” approach. For each USDA Zone from 4 to 9, I research the frost dates for several major cities within that zone using data from authoritative sources like The Old Farmer’s Almanac. I then establish a single, reliable average frost date that serves as my “golden number” for all calculations within that zone.

This is a guideline. It provides a safe and reliable starting point for the vast majority of gardeners in that region.

Step 2: Researching Each Plant’s Unique “Timing Rule”

Next, I dive into the specific needs of each vegetable. Every plant has its own internal clock. I research this “timing rule” from the most reliable sources available, including:

  • University Agricultural Extension Programs: Research-based guides from institutions at the forefront of horticulture.
  • Reputable Seed Companies: Data from companies whose business depends on their customers’ success.
  • Horticultural Research Papers.

This rule tells us when to plant in relation to the frost date. For example, a tomato’s rule might be: “Start seeds indoors 6-8 weeks before the last spring frost.”

Step 3: Putting It All Together: The Calculation

This is where the magic happens. I simply combine the data from the first two steps.

Here’s a real example for a tomato plant in USDA Zone 6:

  • My Zone 6 Baseline (from Step 1): Average Last Spring Frost is May 15.
  • The Tomato’s Rule (from Step 2): Start seeds 6-8 weeks before last frost.
  • The Calculation: May 15 minus 8 weeks = March 20. May 15 minus 6 weeks = April 3.
  • The Result: The recommended window for starting tomato seeds indoors in Zone 6 is March 20 – April 3.

I repeat this exact process for every vegetable in every zone to create the calendars on my site.

How to Find Your Precise Local Frost Date (Highly Recommended)

The calendars I provide are an excellent and safe starting point. However, for the most accurate timing possible for your specific garden, I strongly encourage you to find the frost dates for your local zip code. A garden on a hill may have a later frost date than one in a valley just a few miles away.

You can use the same trusted tool I use:

The Old Farmer’s Almanac Frost Date Calculator (by Zip Code)

Once you have your local frost date, you can easily “fine-tune” my calendars. For example, if your local last frost date is May 22 (one week later than my Zone 6 baseline of May 15), you should shift all my recommended spring planting dates one week later to be extra safe.

My Commitment to You

My commitment is not just to give you data, but to give you understanding. I believe that teaching you how these dates are determined is just as important as providing the dates themselves. This transparency is the foundation of everything I do.

This dedication to meticulous, honest work is the very reason this website was created. You can learn more about my journey on the My Story page.

I hope this explanation gives you full confidence in the information you find here. Now, you have the knowledge not just to follow a calendar, but to truly understand it.