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Harvest, Storage & Post-Harvest TimingStorage Calendar for Seeds
Seeds stay alive longest when they are dry and cool. A simple calendar keeps both homegrown and purchased seed in good shape.
Key points
- Keep seed dry, cool and dark in sealed containers.
- Label every container with crop, variety and year.
- Test germination before planting season.
- Replace short-lived seed more often.
- Put seed tasks on a fixed yearly calendar so they do not get skipped.
What do seeds need to stay viable?
The basics are dryness, cool temperatures and darkness. Moisture and heat shorten seed life. Extension guides from several states repeat this advice, and it applies to both saved seed and leftover packets.
How long a given seed lasts depends on the crop. Onions and parsnips tend to be short-lived, while many others last several years. Look up the range for each crop in an extension chart.
Temperature swings matter too. Seed kept in a space that bounces from warm days to cold nights takes up and loses moisture, which wears it down faster than steady cool storage does. An interior closet or a dedicated box in the refrigerator is steadier than a garage shelf.
When should you dry and clean seed?
Seed from dry-fruited crops such as beans and lettuce should dry on the plant or on screens in a ventilated, shaded spot. Wet-fruited crops such as tomatoes and cucumbers need a cleaning step first, and your extension guide explains the method.
Do not store seed until it is thoroughly dry. A seed that bends instead of snapping, or that feels cool and soft, probably needs more time.
Give each batch a few days on a screen or plate in a dry room before you pack it. Moist seed packed too early can mold in the jar, and that loss is hard to see until planting day.
How do you set up a seed storage calendar?
Pick a few fixed times each year. After harvest, you dry, clean, label and pack. In midwinter, you inventory and test. In late winter, you decide what to buy or order. At the end of the season, you note what failed and why.
For example, if your last spring frost usually falls around mid-May, count back from there to figure out when to run germination tests so you have time to order replacements.
Put these dates on your wall calendar or phone so they happen. Seed work done in a rush in spring is the most common reason for poor stands.
- After harvest: dry, clean, label, pack
- Midwinter: inventory and sort
- Late winter: germination tests
- Spring: order replacements
What containers and places work?
Airtight containers such as glass jars with tight lids keep humidity out. Paper envelopes work if they sit inside a sealed container. Keep them in a cool spot, such as an interior closet or a refrigerator, and away from windows, heaters and attics.
Add drying agents only as your extension guide describes, and label each container with crop, variety and year.
Keep paper packets in a larger sealed jar, and write the crop and year on both the packet and the jar lid. If you use the refrigerator, let the jar warm to room temperature before opening it so moisture does not condense on the seed.
How do you test germination?
A basic germination test uses a small number of seeds on a damp paper towel in a warm place. Count how many sprout after the time listed for the crop and compare to what you expect. Iowa State and other extension offices give the steps.
If germination is low, plant more thickly or replace the seed. A test in winter saves a lot of disappointment in spring. Mark the date on the towel or tray so you know when to count, and write the result on the packet so you do not have to repeat the test.
What mistakes shorten seed life?
The usual causes are damp storage, a hot shed, no labels and mixing years in one jar. Hybrid seed saved from your garden may not come true, so that is a reason to buy fresh seed for hybrids.
Cross-pollination between varieties can also change what you get, and extension seed-saving pages cover isolation basics.
Treat saved seed as a small yearly project with its own calendar. A few notes each season make it easy to keep a variety going for many years.
How do you sort what to keep and what to replace?
Keep seed from your healthiest plants, from varieties that did well in your conditions, and from open-pollinated types that come true. Buy fresh seed for hybrids, short-lived crops and anything that tested weak.
A short list in your calendar helps: crop, variety, year saved, germination result and a keep, use-first or replace decision. That list will save you from buying duplicates and from planting dead seed.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.