Understanding Seed Shelf Life: Key Factors to Consider
Yo! Gardening's a sweet, DIY hobby that keeps you close to the Earth. Seed companies make plants and gather those seeds, selling them for future use. Seeds can last a couple of years, but their germination rate drops over time—not that they ever really "expire." Whether you're a green thumb or a total novice, you've probably got a stash of leftover seed packets from one gardening season to the next. Here's the lowdown on using seeds from previous years.
We chatted with two gardening gurus who spilled the beans on seeds, what to look for on a seed packet, what those dates mean, and the best techniques for storing seeds.
- Stephanie Turner is the Clemson Extension Horticulture Agent and Master Gardener Coordinator for Greenwood County.
- Greg Key is the brains behind Hoss Tools, based in Georgia, and a member of the National Garden Bureau.
What's up with the Dates on Seed Packets?
Those dates on seed packets aren't actually expiration dates. Instead, they're either a sell-by date or a packed-by date. According to Stephanie Turner, Clemson Extension Horticulture Agent and Master Gardener Coordinator for Greenwood County, "Most home garden seed packets contain seeds tested for germination for that particular calendar year." Besides a date, a seed packet will also feature a lot number, country of origin, seller address, and the number or weight of seeds inside. Seeds with good germination rates could be harvested a few years prior, even if the packet says "Packed for 2025."
Many seeds remain viable for multiple years, as long as you store them properly. The dates only provide information about germination's peak, which means a better chance of success when sowing seeds. According to Turner, "Dating is there to assist consumers in making informed decisions and, in some cases, it's a legal requirement."
Why are there Dates on Seed Packets?
Seed packets have dates to help shoppers make informed decisions and for legal purposes. Seeds are regulated at the state and federal levels, and the Federal Seed Act sets labeling standards for vegetable and agricultural seeds across states.
State laws often differ, though, and typically apply to flower seeds. According to Greg Key, the founder of Hoss Tools, "For instance, Georgia requires a germination test every nine months." State laws can also require seed packets to include details about the germination test.
Factors Affecting Seed Viability
A seed's potential to produce a plant is known as its viability. Seed quality at harvest plays a big role in viability and germination. According to Turner, after seeds are harvested, seed viability can be affected by storage conditions, handling procedures, seed treatments, and the duration of storage.
Signs Seeds May Not be Viable
If you've got some leftover seeds from a year (or years) past, you might wonder if they're still any good. Here are some signs to watch for:
- Dry or lighter colors: Aging seeds can become drier and lighter in color over time. However, this isn't always easy to detect without familiarity with the seeds.
- Inability to germinate: The easiest and most accurate way to determine if seeds are viable is to perform a germination test. If fewer than six seeds sprout, it's likely time for new seeds.
On average, seeds can be sown over several growing seasons. Turner says, "Typically, seeds will last 2 to 3 years, but the shelf life varies among species." Radishes, collards, and watermelons can last up to 5 years, while onion seeds usually decline after a year.
How to Perform a Germination Test
To see if your seeds are still in good shape, do a germination test:
- Grab a paper towel, water, and a container or plastic bag.
- Place 10 seeds in a damp paper towel and seal the container or bag.
- Label the container with the plant's name and the date.
- Place the test in a warm spot and check back for germination.
Seed packets should list the time it takes for the seed to germinate. If seven days pass, and only one seed has sprouted, it's probably time to invest in new seeds. If you're curious, you can continue to observe the progress of the seedlings.
Where to Store Seeds
For seeds to last several seasons, they need to be stored correctly. According to Key, "The ideal environment is cool and dry, around 35-45°F and 35-45% humidity." Experts suggest keeping seeds in your refrigerator, nestled in an airtight ziplock bag, away from moisture and warm temperatures. Make sure the container is sealed tightly because humidity can be high in refrigerators.
12 Plants That Aren't Worth Growing From Seed, According to Gardening Pros
- Stephanie Turner, the Clemson Extension Horticulture Agent, states that most home garden seed packets contain seeds tested for germination for the particular calendar year.
- Greg Key, the founder of Hoss Tools, explains that seed packets have dates to help shoppers make informed decisions and for legal purposes, as seeds are regulated at the state and federal levels.
- According to Turner, a seed's potential to produce a plant is known as its viability, and seed quality at harvest plays a big role in viability and germination.
- If seeds from previous years are light in color or fail to germinate, it's likely time for new seeds, as aging seeds can become drier and lighter over time.
- To perform a germination test, place 10 seeds in a damp paper towel, seal the container or bag, label it, and place it in a warm spot to check for germination after seven days.
- For seeds to last several seasons, they should be stored in a cool and dry environment, ideally around 35-45°F and 35-45% humidity, such as in an airtight ziplock bag in the refrigerator, away from moisture and warm temperatures.
