Johnny’s Seeds Seed-Starting Date Calculator: When to Start Your Seeds Indoors

Seed Starting Date Calculator

Find out exactly when to start your seeds indoors and when to transplant them outside

Last Spring Frost Date

Crop

What Is Johnny’s Seeds Seed-Starting Date Calculator?

Johnny’s Seeds Seed-Starting Date Calculator, available at johnnyseeds.com, is a free online tool designed to take the confusion out of one of the most critical steps in gardening: figuring out when to start seeds indoors and when those seedlings are safe to move outside. Developed by Johnny’s Selected Seeds — a respected seed company with decades of experience serving commercial growers and home gardeners alike — this calculator provides precise, crop-by-crop timing recommendations based on your local frost-free date.

The concept behind the tool is simple but powerful. Every vegetable and herb has an optimal window for indoor seed starting that is calculated backward from the date it is safe to set transplants outdoors. For example, if tomatoes need six to eight weeks of indoor growth before transplanting, and your last frost date is May 15, then you should start your tomato seeds around mid-to-late March. The calculator automates this math for dozens of crops simultaneously, saving you from having to look up each variety individually and count weeks on a calendar.

In addition to indoor starting dates, the calculator also provides safe outdoor planting dates — both for transplants started indoors and for seeds that are sown directly in the garden. This dual function makes it a comprehensive timing resource for your entire planting schedule. The tool is completely free and requires no account, making it an essential bookmark for any gardener who starts seeds indoors under lights or on a sunny windowsill.

Key Features

Frost Date-Based Calculations: Enter your last expected spring frost date and the calculator automatically computes indoor seed-starting dates and outdoor transplanting dates for every supported crop.
Dual Indoor and Outdoor Schedules: Get both the dates for starting seeds indoors under grow lights and the dates for direct sowing or transplanting seedlings outside, covering your full season in one view.
Dozens of Crop Varieties: The calculator includes timing data for a wide selection of vegetables, herbs, and flowers commonly started from seed, from quick-growing lettuce to slow-starting peppers and eggplant.
Backed by Johnny’s Research: All timing recommendations are based on Johnny’s Selected Seeds’ extensive trialing and research, giving you dates that reflect real-world growing experience rather than theoretical averages.
Free and Instant: No registration, no subscription, and no waiting — just enter your frost date and get your complete planting schedule in seconds.

Pros and Cons

Pros	Cons
Completely free with no sign-up	You must look up your own frost date first
Backed by professional growing research	Does not auto-detect your location
Covers dozens of vegetables, herbs, and flowers	No garden layout or companion planting features
Calculates both indoor and outdoor dates	Cannot save results within the tool
Fast, clean, and easy to use on any device	Limited to crops in Johnny’s database

Pricing

Johnny’s Seeds Seed-Starting Date Calculator is 100% free to use. There are no subscriptions, premium tiers, or hidden costs of any kind. The tool is provided as a free resource by Johnny’s Selected Seeds as part of their Grower’s Library, which also includes guides on succession planting, pest management, and other growing topics. You do not need to create an account or make a purchase to access the calculator. Simply visit the page, enter your frost-free date, and view your personalized seed-starting schedule instantly.

How to Use Johnny’s Seeds Seed-Starting Date Calculator

The calculator is designed to be as straightforward as possible. Follow these steps to generate your complete seed-starting schedule:

Determine your last spring frost date using the Old Farmer’s Almanac frost date tool or your local university extension office. You will need this date to use the calculator.
Navigate to the calculator at johnnyseeds.com and enter your frost-free date into the input field on the page.
Review the generated schedule which will display a table of crops with two key dates for each: when to start seeds indoors and when the resulting seedlings are safe to transplant outside.
Identify your direct-sow dates for crops that do not need indoor starting. The calculator also shows when it is safe to plant these seeds directly in the ground.
Record your dates by printing the results, writing them in a garden journal, or transferring them to your phone’s calendar so you receive reminders when each planting window arrives.

Who Should Use This Tool?

This calculator is an essential resource for any gardener who starts seeds indoors, whether on a windowsill, under grow lights, or in a greenhouse. It is especially valuable for those growing crops that require a significant head start indoors, such as tomatoes, peppers, eggplant, celery, and onions — all of which need to be started weeks before the last frost. New gardeners who are unsure about the timing of indoor seed starting will find the tool removes all the guesswork. Market gardeners and small-scale commercial growers will appreciate having professionally researched dates from a trusted seed company. Even experienced gardeners who grow many varieties each season will save time by having all the calculations done automatically rather than working through each crop by hand.

Frequently Asked Questions

Where do I find my frost-free date?

You can find your average last spring frost date by entering your ZIP code into the Old Farmer’s Almanac frost date calculator or by contacting your local cooperative extension office. The National Gardening Association also provides frost date lookup tools. Once you have this date, simply enter it into Johnny’s calculator to generate your schedule.

Does the calculator account for fall planting?

The primary version of the calculator focuses on spring seed starting and summer transplanting. For fall crops, you would need to work backward from your first expected fall frost date. Some gardeners use the same calculator by entering their fall frost date in reverse to determine late-summer sowing dates for cool-season vegetables like kale, broccoli, and carrots.

Can I use this calculator if I don’t buy seeds from Johnny’s?

Absolutely. The seed-starting date calculator is a free public resource and works with seeds from any supplier. The timing recommendations are based on the biological needs of each crop, not the specific seed brand. Whether you purchase seeds from Johnny’s, a local garden center, or save your own from year to year, the calculator’s dates will serve you well.