Nasturtiums keep flowering until the first frost turns them to mush overnight — and by then, if you look under the leaves, the ground is usually scattered with their seeds. They are among the easiest seeds of all to save: big, quick to ripen and true to type on most varieties. They also give you a second harvest that most gardeners never try, because the young green seeds make excellent peppery "capers". This guide explains how to save nasturtium seeds — when they are ripe, how to dry them without mould, how to store them — and how to pickle the green ones before the frost arrives, usually in the second half of October in Britain.
- When August until the first frost · mostly from the ground in October
- Ripe when Seed turns from green to tan and corky · drops at a touch
- Drying 2–4 weeks in a single layer, indoors · until rock-hard
- Storage Paper envelope, cool and dry · sow March–May · viable for several years
How nasturtium seeds form
Each nasturtium flower of Tropaeolum majus leaves behind a cluster of three seeds joined at the centre, about the size of a chickpea each. They start bright green, plump and soft, and over three to five weeks they swell, wrinkle, turn pale tan and finally drop off the stalk. Because the plant flowers continuously from midsummer, a single plant carries seeds at every stage at once: green ones you can pickle, half-ripe ones still on the stems, and ripe ones already lying on the soil.
That last group is the easiest harvest in the garden. Ripe nasturtium seeds fall rather than scatter, so they collect directly under the plant. Lift the trailing stems, look on the ground and pick them up by the handful.
Will the seed come true?
Nasturtiums are insect-pollinated, and all varieties of Tropaeolum majus cross with one another. Seed from a single variety grown on its own — the dark-leaved, scarlet 'Empress of India', the creamy 'Milkmaid' or the near-black 'Black Velvet' — will come up much like its parent. Seed from a bed of mixed colours gives you a mix, often a lovely one, but you cannot pick the colours. Compact habit and variegated leaves, as on 'Alaska' and 'Jewel of Africa', mostly carry through, but expect the odd surprise. If a packet was labelled F1, the next generation will be variable, as we explain in heirloom vs F1 vs organic seeds. Semi-double types such as 'Gleam' set less seed than singles, so collect from those early.
How to save nasturtium seeds, step by step
- Collect on a dry day Pick up tan seeds from the ground and pull off any that come away from the stalk at a light touch.
- Rescue full-size green seed before frost If a frost is forecast, take plump green seeds too. Many finish ripening indoors, though germination is lower than from seed that ripened on the plant.
- Separate and clean Break the clusters into single seeds and brush off soil. Throw away any that are soft, hollow or show mould.
- Dry slowly in one layer Spread on a paper-lined tray in a warm, airy room, out of direct sun, for 2–4 weeks. Turn them every few days.
- Test before you pack Fully dry seed is hard, shrivelled and cannot be dented with a fingernail. Any give means it needs longer.
- Store in paper Label paper envelopes with variety and year and keep them in an airtight tin somewhere cool, dry and dark.
Drying is where it goes wrong
Most seeds you save are small and dry out in days. Nasturtium seeds are large and fleshy, and the green ones are mostly water, so they take weeks to dry and will rot in a closed container if packed too soon. Never put them in a plastic bag or jar until they pass the fingernail test, and keep the drying tray in a room with moving air — a spare-room shelf is better than a damp shed. Avoid heat above about 35 °C: a radiator top or oven damages the embryo, as it does for any seed (see our guide to storing and preserving seeds).
Save for sowing
Ripe seed that will germinate next spring.
- Tan, beige or pale brown and corky
- Drops from the stalk or lies on the soil
- Dried until rock-hard
Pickle as capers
Young seed for the kitchen, not for sowing.
- Bright green, plump and still soft
- Picked within 2–3 weeks of the flower fading
- Crisp when bitten, not woody
Pickling green nasturtium seeds as capers
Green nasturtium seeds have the same peppery, mustard-like bite as the leaves and flowers — the flavour comes from the same compounds that make watercress hot. Pickled, they are a good home-grown stand-in for capers in sauces, salads and with fish. Use only young, green, soft seed; anything that has started to turn tan is too hard.
Rinse the seeds and soak them in brine (about one tablespoon of salt to 250 ml of water) for two to three days to soften the raw heat. Drain, pack into a small clean jar and cover with white wine or cider vinegar brought to the boil with a pinch of sugar, a bay leaf and a few peppercorns. Close the jar, let it cool and keep it in the fridge. They are ready after two weeks and keep for several months refrigerated. Only pickle seed from plants you know have not been sprayed.
Common mistakes
- Packing seed before it is dry — the most common cause of a mouldy envelope in January.
- Waiting until after the frost — collect before the first hard frost; green seed on blackened plants rarely ripens.
- Saving from mixed beds and expecting one colour — varieties cross freely. Grow a favourite apart if you want it true.
- Pickling ripe seed — tan seeds are woody and inedible. Capers are green seeds only.
- Forgetting to label — nasturtium seeds all look alike once dry. Write the variety and year on every envelope.
Frequently asked questions
How long do nasturtium seeds stay viable?
Stored cool and dry, typically three to five years, with germination slowly falling each year. If you are unsure about an old batch, run the simple paper-towel test in our guide to how long seeds last.
Do nasturtiums self-seed?
Often. The plants die at the first frost, but seed left on the soil survives a mild winter and comes up in late spring. Self-sown seedlings from mixed plantings will be mixed colours.
When should I sow saved nasturtium seeds?
March to May, after soaking overnight. Sow direct or into the pot they will grow in — nasturtiums dislike root disturbance, as noted in our container gardening guide. Climbing types are among the easiest climbers to grow from seed.
Are nasturtium seeds safe to eat?
Yes, nasturtium leaves, flowers and young seeds are all edible, and widely eaten. They are strongly peppery, so use them in small amounts — and never eat seed that has been treated or coated for sowing.
Five minutes under the leaves this month gives you next year's nasturtiums and a jar of capers into the bargain. Nasturtiums also earn their place beside vegetables as a trap crop — see companion planting. If you are new to sowing flowers, start with our beginner's guide to growing flowers from seed. Browse the Tropaeolum majus and edible flowers collections, the wider annual flowers, or all our seeds, and keep our growing guides to hand.
