Seed Packet Dates Explained: How Long Seeds Stay Viable

A shoebox of seed packets is one of the small pleasures of January. Then you start flicking through them and the doubts creep in: that tomato packet from two seasons ago, the parsnips with the faded ink, the beans you split with a neighbour. The date on the corner looks official, but it rarely means what gardeners assume. Seeds do not expire on a set date the way milk does. They fade, slowly, at a rate that depends on the species and — more than most people realise — on where the packet has spent the last two summers.

What the Date on a Seed Packet Actually Means

Most packets carry one of three things: a "packed for" year, a "sell by" date, or a "tested" date. In all three cases, the stamp records when the seeds were packed or last germination-tested for the seller. It is not an expiry date, and a packet dated last year is not automatically dead.

Many packets also print a germination percentage — something like "germination 92%". That figure describes the batch at the time of testing, in the supplier's conditions. It is genuinely useful, because a batch that started at 95% has more room to fall than one that started at 70%, but it says nothing about how the seeds have been treated since.

The practical takeaway: treat the date as a rough guide to age, not a verdict. A three-year-old packet of tomato seed kept in a cool, dry tin will usually outperform a fresh packet left in a hot greenhouse.

How Long Different Seeds Stay Viable

Seed longevity varies enormously between species, and the ranges below assume reasonably cool, dry storage. Push the envelope — a shed that bakes in July — and cut them substantially.

• Short-lived (one to two years): parsnips, onions, leeks, parsley, celery, sweet corn, salsify. Parsnip is the classic case: sow fresh seed and don't expect much from a two-year-old packet.
• Medium (two to four years): carrots, peas, beans, spinach, chard, most brassicas, fennel, dill. Peas and beans germinate well but are prone to weevils and rot if stored warm or damp.
• Long-lived (four to six years or more): tomatoes, peppers, aubergines, cucumbers, squash, melons, radishes, lettuce, beetroot, basil. Tomatoes are famously durable; many gardeners have germinated seed a decade old.
• Hard-coated seeds: sweet peas, lupins, morning glory and other tough-coated flowers can stay viable for five years or more, though the seed coat may need nicking or soaking to let water in.
• Flower annuals: most keep around two to three years; marigolds, nasturtiums and calendula lean toward the longer end.

These are working ranges, not rules. A cool, dark, dry box can add years to a packet. A hot, humid drawer can strip them away in a single season.

Storage Matters More Than the Date

Two things kill seeds: heat and moisture, usually together. The worst place in most houses is the shed or greenhouse, where temperatures swing from frost to forty degrees and condensation forms inside the packets. The second worst is the kitchen drawer next to the oven.

Aim for cool, dark and dry, and keep it stable. A sealed tin or a glass jar in a cupboard works well. For longer storage, put the packets in a zip-top bag with a sachet of silica gel and keep it in the fridge — not the freezer, unless you know the seed was dried properly. Let the jar come to room temperature before opening it, or condensation will form on the cold seeds.

Oily seeds — parsley, onion, celery, anything in the carrot family — lose viability fastest, which is why they top the short-lived list. Starchy, hard-coated seeds such as beans and squash are tougher.

Reading the Clues Beyond the Date

Look at the seeds themselves before you look at the label.

• Shrivelled or cracked seeds have probably dried too hard or too fast. They may still germinate, but expect a lower rate.
• Powdery mould or a musty smell means moisture got in. Discard those packets.
• Small holes in the seeds or fine dust in the bag suggest weevils or other insects have been feeding.
• Faded, brittle packets are a hint that they have been sitting in light and heat, even if the date looks recent.

Home-saved seed is often a different story. If you dried it properly and stored it cool, it frequently germinates better than commercial seed of the same age, because you know exactly how it was handled. Just label it clearly; a bare envelope of small brown seeds tells you nothing in March.

The Paper Towel Test

When you genuinely cannot tell, ten minutes of work settles it. This test gives you a real germination percentage for that specific packet, rather than a guess based on the year stamped on it.

1. Count ten seeds. Ten makes the maths simple: each sprout is worth ten percent. If you have plenty of seed and want more precision, use twenty.
2. Dampen a paper towel until it is moist but not dripping, and squeeze out the excess water.
3. Space the seeds on one half, fold the towel over, and slide it into a labelled zip-top bag or sealed container. Write the variety and the date on it — you will forget.
4. Keep it warm, around 20 to 22°C (68 to 72°F), out of direct sun. The top of a fridge or a warm cupboard is fine.
5. Check every two days. Most vegetables show a root within a week to ten days; peppers and aubergines can take two to three weeks, so don't give up early.
6. Count the seeds with a visible root — not just a swollen coat — and multiply by ten. That is your germination rate.

One caveat: a few seeds, lettuce and celery among them, germinate better with light. The towel test still works, but don't bury them under a second layer of paper.

Putting the Numbers to Work

So you have a result. What now?

• Above 80 percent: sow as you normally would.
• 50 to 70 percent: perfectly usable. Sow about half again as thick and thin later.
• Below 50 percent: fine for crops you raise in modules and can afford to gap up, or for a thick sowing of salad leaves you will cut young. A poor choice for anything direct-sown at precise spacing, like carrots or parsnips, where gaps are hard to fix.
• Nothing germinated: compost it. No amount of optimism will revive a dead packet.

A Five-Minute Seed Audit

Do this once, at the start of the season, and you will stop re-buying things you already own.

Empty the box onto a table and make three piles: sow this year, test first, and compost. Be honest. Anything short-lived and more than two years old goes straight into the test pile — parsnips, onions and parsley especially. Tomatoes, lettuce and brassicas can usually stay in the sow pile unless the packet looks rough.

Then write the year on every packet in thick marker, so next January you are not squinting at faded ink. Keep the test results on the packet too; a pencil note saying "60%, 2025" is more useful than any printed date.

And plant the old favourites first. A packet you have been saving for a good year is not improving with age, and a slightly thin row of last year's beans beats no row at all.

Photo: Ylanite / Pixabay