Is That Old Seed Packet Still Worth Sowing? How to Test Viability Before You Waste a Sowing Slot

You open the seed drawer in February and find a half-used packet of parsnip seed from two seasons ago, a few tomato packets with a sell-by date that's long gone, and some onion seed you bought "sometime after the pandemic." The packet looks fine and the seed looks fine, but looks tell you almost nothing about whether it will grow. The reliable check is a 10-seed damp paper towel test that takes two weeks and costs almost nothing.

Sow blind and you won't know there's a problem until three or four weeks later, when the bed is still bare. Scotland's frost-free window is short and varies by region (see the frost dates guide), so a failed early sowing often leaves too little season to start again, and the space, the slot and sometimes the variety are gone for the year. Testing a pinch of seed first costs a fortnight and a damp paper towel. The test and figures below are for shop-bought seed that has sat since a previous year. Seed you collected yourself keeps differently and has its own pitfalls (drying, keeping varieties from cross-pollinating, and storage from the day you collect it); the saving-your-own-seed guide covers those, and the same paper towel test works for it.

The paper towel germination test

1. Count out 10 seeds from the packet. Ten gives you a workable percentage without wasting seed you might still need.
2. Dampen a paper towel so it's moist throughout but not dripping; squeeze out any excess water first.
3. Space the seeds out on one half of the towel, then fold the other half over them (or lay a second damp sheet on top). Gardeners' World lays the seed in rows on damp kitchen towel on a plate, which makes the seeds easy to identify.
4. Cover or seal it inside a plastic bag or with clingfilm over a plate, and label it with the crop and date. It's easy to lose track of which is which when you're testing several packets.
5. Keep it somewhere warm, such as an airing cupboard, on top of the fridge, or near (not on) a radiator. Most vegetable seed germinatesA seed sprouting: breaking dormancy and putting out its first root and shoot, given the right warmth and moisture. Full definition → fastest at somewhere around the high teens to low twenties °C.
6. Check every day or two. Keep the towel damp, misting it or adding a little water if it dries out, but don't let it get waterlogged: seed sitting in standing water can rot before it germinates.
7. Give it a full two weeks before writing anything off. After two weeks most viable seed should have sprouted, and slower seed such as parsnip or celery can take most of that time even when perfectly healthy. Don't judge the result at day four.
8. Count what's germinated. A visible root (radicle) is enough to count a seed as successful; you don't need to wait for leaves. Multiply the germinated seeds by 10 for your percentage: five out of ten is 50% viability.

Test each variety separately, because germination speed and rate vary between crops and sometimes between varieties, and mixing them in one bag makes the count harder to trust. Seeds that sprout are proven viable, so pot them on into modulesA tray divided into small individual cells, each sown with its own seed or seedling, so each plant grows undisturbed roots until it's ready to plant out. Full definition → or small pots rather than discarding them, handling the fragile root gently. Ten seeds isn't a sowing on its own: once you know the packet's real germination rate, sow the rest at the rate the result calls for (see the table below). Pelleted or coated seed, common for carrot, can be tested the same way, though the coating makes the seed harder to inspect by eye.

How long does shop-bought seed last?

The spread between species is bigger than most people expect. Some vegetable seed is use-it-or-lose-it; other seed is still worth testing years after the packet date.

Parsnips and alliums are the ones to be suspicious of first. If you find old onion or parsnip seed in the drawer, don't assume it's fine because everything else has kept for years: test it, or buy fresh.

What "stored well" means

Longevity figures only hold if the seed has been kept properly. A packet that has spent two summers on a sunny windowsill, or in a shed that swings from freezing to warm, isn't the same as one kept consistently cool.

Moisture and warmth shorten a seed's life. A rough rule of thumb is that storage life doubles for every 5°C drop in temperature and every 1% drop in moisture content. The RHS advises storing dry seed in labelled paper packets or envelopes in an airtight container with some desiccant (calcium chloride or silica gel) in a refrigerator at 5°C (41°F), where most seed will remain viable for many years.

In practice, "stored well" means:

• Cool: a cold cupboard, unheated room or the fridge. For most home-stored vegetable seed, stick to the fridge: Garden Organic also lists the freezer, but only for seed that has been properly dried first.
• Dark: light works against the seed, and the heat that comes with a sunny spot matters even more.
• Dry: damp packets and high humidity are a major cause of seed dying in storage, because excess humidity or warmth can cause seed to deteriorate or die from fungal disease or rotting.
• Away from temperature swings: a shed, garage or windowsill that heats up by day and cools sharply at night is probably worse for seed than a steady, moderate cupboard, even if the cupboard isn't as cold as a fridge.

If your old packet has lived in anything other than these conditions, treat the typical figures above as optimistic best cases. Let a packet from the fridge come up to room temperature before opening it, so condensation doesn't get in.

Signs the seed is already dead

Two quick checks can save you the full test:

• Visible mould or fungal growth on the seed or inside the packet means it has been exposed to damp at some point. Seed in that state is very unlikely to be worth testing.
• The float test, for medium-to-large seeds (beans, peas, squash, sweetcorn and similar; it's unlikely to work on very small or light seed like carrot or lettuce). Put a sample in a jar of water: viable seed sinks and dead seed floats. It's not infallible, but for larger seed it's a useful first pass before committing two weeks to a full test.

If either check shows a problem, skip the paper towel test and buy fresh.

Reading the result: sow as normal, sow extra, or bin it

The lower the percentage, the more seed you'll need to sow to get a decent crop.

These bands are guidance rather than an exact formula, and a crop that isn't your main harvest might be worth sowing at a lower rate than one you're relying on.

Tomatoes, peppers and other seed that needs extra warmth

Tomatoes, peppers and other seed that tends to germinate best above 20°C need the test to run warmer than an ordinary cupboard reliably manages. A spot on top of the fridge, near (not on) a radiator, or a heated propagator lid is worth using for these. If none germinate, check the warmth before writing off the packet, because a cold test environment can give a false "dead seed" result.

A packet that tests well can still sit and rot, or simply not come up, if it's sown into ground that's too cold. The test rules out the seed, not the conditions it goes into afterwards.

Regional variation within Scotland

A Highland or Aberdeenshire frost-free window is likely to run shorter than a milder coastal or Central Belt one, so there's less room to recover from a patchy sowing. In those gardens, lean towards buying fresh when a result lands in the lower bands. The frost dates guide gives the figures by region: check it before deciding how much risk a lower-band result is worth where you garden.

Common questions

Sources