The beginning of spring usually sees me sprawled in the middle of the living room floor, with all my ammo boxes, laying out rows and rows of seed packets sorted by vegetable, and then by variety.
Some are even color-coded… and I suddenly realize I have a rather strange obsession with collecting 12 different types of purple tomatoes (and counting).
Inevitably, a handful of seed packets get tossed in the compost pile as I double-check the dates… peppers from 2016, onions from three years ago. Yikes.
Some seeds I’ve only sown once or twice but still have half a packet left, some I’ve saved… and saved… and saved… because they’re so easy to save by the bagful every year (I’m looking at you, beans).
Others are rotated every few seasons as I try new varieties, and by the time I make it back to those Parisienne carrots, it’s already been a couple years.
Are they still good? Should I get new ones? How long do seeds really last, anyway?
I’ve combed through countless seed sites and extension sites over the years, wondering this very question.
How long do seeds last?
There seems to be no consensus, especially when you take into account the environment the seeds were stored in, the quality of the original crop the seeds were harvested from, and even the condition of the seeds themselves, as treated seeds will have a different lifespan than seeds in their natural state.
Seeds have a shelf life (as all living things do), and depending on where your particular shelf is, the viability of your seeds can vary by as much as a year or two.
When someone asks, “How long do broccoli seeds last?” a safe answer is three years, but in ideal conditions your seeds could still actually sprout after five.
So, you see where our dilemma lies.
What are ideal storage conditions for seeds?
In a perfect world, we’d all have second refrigerators with perfectly controlled humidity levels in which to store our seeds.
Our seeds would live in this cool, dark, dry environment and 10 years later, those very first tomato seeds we’d ever bought would still be viable.
In reality, our homes go from hot to cold at the turn of the seasons, we sometimes forget our seed packets outside overnight (or at least I do), and an old shoebox will have to do for storage.
We can’t really fault ourselves either. Who knows what the seed went through before it even reached the store?
What temperature should you store seeds at?
With all the uncertainty about how and where seeds should be stored, here’s a proven fact:
Seeds store best below 40°F with less than 10 percent humidity, tucked inside airtight containers in a dark environment.
Every time a seed experiences less than ideal conditions, it suffers a decline in quality. It may not die right away, but it might take a little longer to germinate. Eventually, it will fail to germinate at all.
Using the baggie method with coffee filters (or paper towels) is a good way to test seed germination.
A good rule of thumb to know: less than 50 percent germination rate means it’s time to buy new seeds.
Why seed vigor matters
According to Oregon State University, vigor is the “ability of those seeds to produce normal seedlings under less than optimum or adverse growing conditions similar to those which may occur in the field.”
That is, the ability of your plants to survive in the ground outside with all the elements working against them (even if they’ve been hardened off), as opposed to being coddled inside in a cozy baggie.
While a germination test can predict viability, it can’t truly predict vigor: how well a seedling will grow in terms of health, strength, uniformity, and root system, not to mention its production of flowers and fruits.
A seedling with compromised vigor may have a missing cotyledon, look stunted or scrawny, or seem overall slower to develop than seedlings from fresher seeds.
Try as they might, sometimes older seeds just don’t have it in them to sprout, grow, and go all the way to seed again. A will to germinate does not equal an ability to thrive.
What the pros say about the average lifespan of seeds
The cheat sheet below takes the average life expectancy of seeds from a variety of sources, including the cooperative extensions of Oregon State University, Colorado State University, Purdue University, and Virginia State University.
Consider it more as a guideline, as the shelf life of your seeds ultimately depends on the date on the packet and how carefully you’ve stored them since then.
Garden Betty’s Seed Life Cheat Sheet
|Brussels sprouts||4 years|
|Corn (sweet)||2 years|
|Oriental greens||3 years|
|Squash (summer and winter)||4 years|
|Herbs and Flowers||Shelf Life|
|Annual flowers||1 to 3 years|
|Perennial flowers||2 to 4 years|
Common questions about storing seeds
Can you freeze seeds to make them last longer?
Yes. All seed banks freeze seeds that are intended for long-term storage, and you can do the same at home.
The key is to start with thoroughly dried seeds (if you saved them from your own plants) and store them in airtight, freeze-proof containers to reduce the risk of seeds absorbing moisture. Keep the seeds in a reliable freezer that maintains consistent temperatures and isn’t opened often.
When it’s time to plant, thaw the frozen seeds overnight at room temperature before planting them.
What temperature will kill seeds?
Seeds begin to die at temperatures above 108°F and are completely sterilized at 140°F (which usually happens in hot compost piles). However, it only takes consistent high temperatures over 90°F to affect the embryo inside a seed and lessen the chances of germination.
Avoid storing your seeds in an attic or uninsulated garage, or inside a hot car on a sunny day. If ideal storage conditions below 40°F with less than 10 percent humidity aren’t possible, keep your seeds in the coolest (and driest) part of the house, like a closet in a north-facing room or a dehumidified basement.
Should you vacuum seal seeds?
If you want to store seeds long-term, vacuum sealing is the ultimate method of seed preservation. Start with very dry seeds (they should shatter or snap in half cleanly, rather than smash or bend under pressure) before vacuum sealing them in a plastic bag and storing them in a fridge or freezer (below 40°F).
Do seeds need air in storage?
No. In fact, seeds store best in airtight containers in consistently cool, dark, and dry conditions, such as those found in a fridge or freezer.
As long as the seeds were sufficiently dry before storage (they shatter or snap in half cleanly, rather than smash or bend under pressure), the lack of air—along with low humidity—helps them stay dormant and viable longer.
Do seeds expire?
Seeds don’t necessarily “expire” or go bad (unless they’re left in conditions that cause them to mold or rot). However, they do deteriorate in quality and vigor over time. Think of the dates printed on seed packets like those “Best by” dates on food; they aren’t set in stone, but are more of a guideline as to how long the seeds are at their peak viability.
If you try to plant seeds past those dates, you may still get a few of them to germinate, but the overall yield will be lower.
This post updated from an article that originally appeared on March 17, 2015.