The gardening year has come full circle. After sowing, growing, flowering and fruiting, saving the seed is the final, vital and fun part of the process.

We can’t save some of the seed, like F1 hybrids. Breeders have created them by crossing varieties. But the final cross doesn’t remain stable beyond the first generation and subsequent ones can be a new combination or reversion to a parent.

And when breeding some flowers, pollination has been sacrificed in favour of larger showier blooms. These do not contain the sexual parts needed for seed creation.

Only naturally open-pollinated or self-fertile varieties of veg and flowers produce viable seed.

Some open-pollinated plants, like the Borage we need for wine cups and Chervil, self-seed in situ. My seakale and wild cabbage can actually overdo it.

Others are equally obliging. When cutting back foxglove or aquilegia stems, I simply shake out the ripe seed where I’d like next year’s plants to grow.

But promiscuous open-pollinators can give you a surprise. Expect any colour combinations from an Aquilegia. And after planting what I thought was a squash, a squash/courgette cross emerged. It grew like a courgette and the fruits were squash.

So, you’ll need to isolate the likes of brassicas or tomatoes to force self-pollination. This is fiddly when growing more than one tomato variety, but easy with brassicas. Only let your selected type, say kale, flower and set seed.

And don’t delay collection or someone else may get there before you. This year, after harvesting some Cerinthe major seed, I went back for more. Too late. I found a pile of empty bracts hidden beneath a block of nearby beetroot. A vole or wood mouse had been tucking in while nibbling some beetroot.

If new to seed saving, start with large seed and avoid the dust-like seed of Nicotiana or Agastache. Many vegetable seeds are a cinch, especially peas and beans.

The large seeds of nasturtiums are also easy. Often two or three ribbed seeds cluster on the end of a springy stalk and are ready for collection when brown.

Always collect dry, ripe seed and during a wet spell cut stalks and store upside down in a shed to finish drying. Place a paper sheet beneath to catch the seed as it falls. You’ll probably need to lend a helping hand by shuggling the stalks.

Then store the completely dry seed in a paper envelope, marking date as well as variety. Never store in plastic as this rots seed.

Most seed obediently germinates when it suits you, so should simply be stored in a cool, dry place. I find my seed drawer is ideal. But a few species like Meconopsis need winter chilling. Their dormancy is only broken by this stratification so need to be sown now and left outside.

Whether you’ve saved or bought seed, how can you tell if it’s viable or not? Some types last for years, one or two for millennia, but others are past it after a year or two.

We all know alliums and parsnips must be fresh, but most others steadily become less viable so it pays to test older stock. Since seed companies are constantly reducing numbers in a packet, you’ll only have surpluses if you save your own.

Place at least 10 seeds on a damp piece of kitchen towel, fold, and place in a clear plastic bag. Put in a warm place for a few days, checking the paper remains moist. Seed should germinate, probably within a week, depending on the variety.

You then know the percentage of success and can sow accordingly.

Plant of the week

Chelone glabra flowers from late summer and prefers moist soil. Its white flowers have rounded tops and cluster close to the stem, they are particularly effective in partial shade.