About Seed Planner

The Seed Starting Schedule was born from a simple frustration: counting backward from frost dates on a physical calendar is tedious and error-prone. We built this tool to help gardeners of all skill levels precisely time their indoor sowing for a more successful 2026 harvest.

How It Works

Our calculator combines two critical data points. We offer two ways to find your schedule: you can select your USDA Hardiness Zone manually, or use our new ZIP Code Search to instantly detect your zone and local climatology for 2026.

The engine uses the 2023 USDA Plant Hardiness Zone averages to determine when your last spring frost is likely to occur. Second, it applies crop-specific "weeks-head-start" logic recommended by university agriculture extensions.

Our Data Sources

Every planting date on this site is grounded in reliable, publicly available data. Our primary source is the 2023 USDA Plant Hardiness Zone Map, which provides the most up-to-date average annual minimum winter temperatures for every region of the United States. We combine this with frost date data from the National Oceanic and Atmospheric Administration (NOAA) to determine realistic last-spring and first-fall frost windows for each zone.

For crop-specific growing requirements — such as days to maturity, optimal soil temperatures, and recommended weeks-head-start for indoor seeding — we draw on recommendations from university agriculture extension services including Cornell, Oregon State, North Carolina State, and the University of California. We also reference the Old Farmer's Almanac and the National Gardening Association for regional growing tips and validated planting windows.

All dates are reviewed and updated annually to account for shifting climate patterns. We cross-reference multiple data points to ensure our calculator gives you a safe, practical planting window — not just a theoretical average.

Why We Built This

The Altto team believes that growing your own food should be accessible to everyone. We noticed that most planting calendars are either too generic (one-size-fits-all dates) or too technical (requiring you to manually calculate backward from frost dates). Our mission is to bridge that gap with a tool that is both accurate and dead simple to use.

We are gardeners ourselves — we know the disappointment of losing seedlings to an early frost or the frustration of starting tomatoes too late and waiting until September for the first ripe fruit. This tool exists to help you avoid those mistakes and enjoy a more productive, less stressful gardening season.

All of our calculators are and will remain free. We fund this project through unobtrusive ads and affiliate links — we only recommend products we actually use in our own gardens. If you find the tool helpful, sharing it with a fellow gardener is the best thanks you can give us.

We believe that local gardening shouldn't be complicated. By providing these tools for free, we hope to encourage more people to grow their own food, support local pollinators, and connect with their local ecosystem.