Planting old seeds is one of those garden problems that feels small… until you’ve waited 10-14 days and nothing comes up.
That’s exactly why I built this Seed Viability Calculator, a free tool that helps you estimate whether your seeds are still likely to sprout, and how many seeds you should sow per hole to get a good stand.
It’s designed for real-life seed situations:
- packets from last year (or five years ago)
- seeds stored in a drawer or garage
- seeds you saved yourself
- “I don’t want to waste space in my raised bed” planting
If you’re completely new to growing food, you may also want to start with my Vegetable Gardening for Beginners guide to learn the basics before planting.
What “Seed Viability” Means (In Plain English)
Seed viability is simply how likely a seed is to germinate.
If your seeds have 80% viability, that means:
- About 8 out of 10 seeds might sprout (in decent conditions)
If they have 30% viability, you’ll likely get:
- spotty germination and empty holes unless you sow extra
This tool turns that uncertainty into a clear plan.
Why a Seed Viability Calculator Saves You a Lot of Frustration
Most gardeners don’t fail because they’re “bad at gardening.”
They fail because they start with seeds that aren’t strong anymore.
Old or poorly stored seeds can lead to:
- empty rows
- wasted seed-starting trays
- uneven spacing (crowding where seeds sprouted, bare patches where they didn’t)
- late planting because you have to start over
This tool helps you avoid that by answering two big questions:
- Are these seeds worth planting?
- How many should I sow per spot to get reliable germination?
How to Use the Seed Viability Calculator (Quick Steps)
- Choose your vegetable or herb
- Enter the year on the packet (or the year you bought them)
- Optional: enter your paper towel test result (10 seeds)
- (Optional) Switch to Advanced and choose realistic storage conditions
- Choose your target success per spot (recommended is 80%)
- Get:
- estimated germination %
- seeds to sow per hole
- total seed estimate (if you add the number of spots)
Beginner Tip: Do a 10-Seed Germination Test (Most Accurate)
If you want the most accurate answer, do this:
- Put 10 seeds on a damp paper towel
- Fold, place in a bag/container
- Keep warm for 7-10 days
- Count how many sprout
Then select:
“Yes (use my result)” in the tool.
That instantly turns this from an estimate into a near-real result.
What the Tool Calculates (And Why It Works)
The calculator combines:
- seed age (based on the packet year)
- typical shelf-life of that crop (some seeds last longer than others)
- optional storage conditions (heat + humidity speed up decline)
- your target success rate (70/80/90%)
Then it recommends how many seeds to sow per spot so you don’t end up with gaps.
How Many Seeds Should You Plant Per Hole?
This depends on viability.
Example:
- Strong seeds (80-90%): often 1-2 seeds per hole
- Older seeds (40-60%): often 2-4 seeds per hole
- Weak seeds (under 35%): You may need 4-6 seeds, or it may be smarter to buy fresh seed
When It’s Better to Buy Fresh Seeds
Sometimes the best advice is: don’t fight the seed.
You’ll usually save time by buying new seed when:
- viability is very low (tool shows low/very low)
- You’re planting a short-season crop and can’t afford delays
- you’re growing something space-limited (containers, small raised beds)
Best Storage Tips (So Seeds Last Longer Next Season)
If you want your seeds to stay viable longer, the goal is:
cool + dry + dark + sealed
Easy version:
- Keep seeds in a jar or zip bag
- Add a silica packet (optional)
- store in a cool closet or fridge
Avoid:
- hot garages
- humid kitchens
- open packets in drawers
Internal link suggestion:
- A future supporting post idea:
- How to Store Seeds Properly (So They Stay Viable Longer)
This tool + that article would rank well together.
Who This Tool Is For
This seed viability calculator is useful for:
- beginner gardeners with leftover packets
- raised bed gardeners who don’t want empty squares
- seed-starters who want reliable tray germination
- gardeners who save seed and want quick decisions before planting
If you’re planning a bed layout, use it together with the square foot gardening planner, so you don’t waste squares on weak seeds.
Common Seed Mistakes This Tool Helps Prevent
- Sowing 1 seed per hole when viability is low
- replanting the whole row instead of just empty spots
- overcrowding because “all the seeds sprouted… finally”
- blaming soil or watering when the real issue was old seed
Conclusion
Old seeds don’t have to be a gamble.
This Seed Viability Calculator gives you a realistic germination estimate, tells you how many seeds to sow per spot, and helps you avoid wasted space, especially in raised beds and small gardens.
Use it before you plant, and you’ll start the season with more confidence (and fewer empty holes).