Why Bother Storing Seeds Carefully?

There is a particular kind of disappointment that comes with sowing a tray of seeds in March and waiting three weeks for absolutely nothing to appear. More often than not, the fault lies not with your sowing technique but with how those seeds spent the previous six months. Left in a shed that swings between damp and baking, or in a paper packet on a sunny windowsill, seeds lose vigour surprisingly quickly. Treat them well, though, and most will still be raring to go two, three, even five years down the line.

In the UK, our damp winters are the real enemy. A seed is a living thing in suspended animation, and it responds badly to moisture in the air around it. Get the storage basics right and you will save money, protect favourite varieties you have saved yourself, and avoid the scramble for replacements every February.

The Three Enemies: Damp, Warmth and Light

Almost everything that goes wrong with stored seed comes down to one of these three. Understanding why helps you make sensible choices rather than just following rules.

• Damp encourages mould and triggers the seed's internal chemistry into thinking spring has arrived. Once that process starts and then dries out again, the seed is usually finished.
• Warmth speeds up the natural decline in viability. Every ten degrees of extra heat roughly doubles the rate at which a seed ages.
• Light, particularly bright sunlight, degrades the seed coat and the delicate tissues inside over time.

The ideal is a cool, dark, dry place with a steady temperature, somewhere around 5°C is excellent, though a consistent 10-15°C in a cupboard will do perfectly well for a single season.

Paper Envelopes or Airtight Jars?

Both have their place, and the trick is often to use them together. Paper envelopes let seeds breathe, which suits anything that went into the packet slightly under-dry, and they are ideal for short-term storage of a season or two. Write on them in pencil or permanent ink, because biro fades and pencil does not smudge when damp.

For anything you plan to keep longer, an airtight container is better. Small glass jars with a rubber seal, old vitamin tubs, or metal tins all work well. Add a sachet of silica gel, or a tablespoon of dry rice wrapped in a twist of kitchen paper, to mop up any residual moisture. If you are using paper envelopes and want the best of both, slip the labelled envelopes inside a sealed jar or tin. That way the seeds stay dry but you still have the individual packets for sorting.

A word of caution: do not put damp seeds straight into a sealed jar. Leave them to dry on a saucer in a warm, airy room for a week or two first, then seal them away.

Label Everything, and Label It Properly

It sounds obvious, and yet every gardener has at some point sown a mysterious packet labelled only "seeds". Good labelling costs nothing and saves a lot of guessing.

• Write the variety name in full, not just "tomato".
• Add the year the seed was saved or bought. This is the single most useful piece of information when you are deciding what to sow.
• Note anything distinctive: "best cropper 2024", "from Dad's plot", "needs support".
• Keep the original commercial packet if there is one, as it usually has sowing depth and spacing printed on it.

Where to Keep Them

A cool, dark cupboard in an unheated room, a garage that does not freeze, or the bottom of a wardrobe all work well. A fridge is fine for long-term storage of larger seeds such as beans and peas, provided they are in a genuinely airtight container, because a fridge is a damp environment. Bring them out and let them come to room temperature before sowing, and never store seeds in the freezer unless you know exactly what you are doing.

Wherever you choose, keep the temperature steady. A shed that bakes in July and freezes in January is the worst of all worlds.

Testing Germination Before You Sow

Before you commit a whole bed to a packet of uncertain age, run a quick germination test in late winter. Count out ten seeds and space them on a piece of damp kitchen paper. Fold it over, slide it into a sealed plastic bag, and keep it somewhere warm, around 18-20°C. Check every couple of days and keep the paper damp but not sodden.

Most seeds will show a root within seven to fourteen days; slower ones such as parsnip may take three weeks. If eight or more germinate, sow as normal. Five to seven and you can still sow, but thickly. Fewer than five and it is time to buy fresh.

As a rough guide to shelf life, expect parsnip and onion to last a year at best, carrots and lettuce three years, brassicas four or five, and tomatoes and beans four to six. Get into the habit of testing, labelling and storing well each autumn, and you will never again be left staring at a bare tray wondering what went wrong.