Which plants come true
Save seed from a tomato and you will probably get a tomato. Save it from a courgette and you might get something else entirely — here is why.
What the terms mean
- comes true — produces offspring that match the parent in the characteristics that matter
- self-pollinating — fertilises itself before the flower opens; pollen does not travel between plants
- cross-pollinating — relies on insects or wind to carry pollen between plants, including to different varieties
- F1 hybrid — first-generation cross between two inbred lines; the seed packet will say F1
- heterosis — the vigour boost seen in F1 generation plants, sometimes called hybrid vigour
- open-pollinated — pollinated naturally and consistently; seed can be saved and will come true (if not crossed)
- F2 generation — offspring of F1 plants; genetically variable and unpredictable
The difference between stable and promiscuous
A plant "comes true" when the seedling it produces matches the parent in all the ways that matter: flavour, colour, form, habit. Whether it does depends on how that seed was made — specifically, on whether the plant was pollinated by something unlike itself before the seed formed.
Self-pollinating plants are the easy category. Tomatoes, French beans, peas and lettuce fertilise themselves before the flower even fully opens. The pollen travels only inches, from anther to stigma on the same flower, so there is rarely a stray father in the picture. Seed saved from these will come true generation after generation, which is exactly why they have been saved by gardeners for centuries. A named heritage tomato variety, kept properly, can remain genetically stable across decades.
Cross-pollinating plants are the complication. Courgettes, squashes, cucumbers, brassicas, sweetcorn and most biennials like beetroot and parsnip actively exchange pollen with neighbouring plants — often with the help of bees that have just visited something related. Save seed from a courgette grown next to a pumpkin and you may harvest something edible but unrecognisable: the offspring will be a genetic shuffle of both parents. It is not dangerous, just unpredictable. The same applies to kale grown near Brussels sprouts, or a parsnip left to seed in a garden where the neighbour has one flowering over the fence.
Then there is a third category: F1 hybrids. These are deliberate crosses between two inbred parent lines, and the resulting seed is sold because the first generation shows exceptional vigour — a phenomenon plant breeders call heterosis. The plants perform reliably, but saving seed from them produces the second, or F2, generation, which splits unpredictably across a range of possible combinations. You might grow fifty seedlings and get fifty different plants. It is not harmful to try, but it is rarely worth the effort if consistency is what you want. The packet will say F1 clearly; open-pollinated or heritage varieties will not.
The practical rule: save from self-pollinators first. Tomatoes, peas and French beans reward the beginner immediately. Once you understand the principle, you can attempt cross-pollinators by isolating them — growing a single variety under fleece during flowering, or timing plantings so related species are not in flower simultaneously. But that is a project for another season. For a first attempt, grow one named heritage tomato, let one fruit ripen fully on the vine, and dry and store the seed correctly. The result will be recognisably itself next year.
Where we stop
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