Here's a simple guide on how to save yourself loads of money by raising your own seeds. Although it won't work for all vegetables, for the ones listed below it's so easy it's daft not to and the seeds you end up with are far better than any you could buy.
My bolt of lightening came when I was just about to buy a packet of butternut squash seeds, more the £2 for about ten seeds. Suddenly had a brainwave... to buy a butternut squash from the local supermarket costs less than £2 and as well as the enjoyment of eating I'd be left with loads more seeds than just ten.
I've also saved my own leek seeds by allowing a couple of plants to mature, enjoying the resultant flowers and ending up with several years supply of leek seeds.
Some basic ground rules
When selecting plants to mature, it's pretty obvious you should pick healthy plants that are disease free.
Not all vegetable seeds can be used, so don't use hybrids or plants that cross pollinate freely. You may still be unlucky since some of the plants listed may still cross pollinate with other varieties nearby, but by following the instructions it's less likely. If unlucky, just try again the following year.
After carefully extracting the matured seeds, give them a clean, removing any chaff, and ensure they're thoroughly dried. When drying, don't use excessive heat. A gentle warmth is best.
Ideally store in a sealed paper envelope with the variety and year noted on the outside and place in an airtight container. Plastic bags or glass containers are less ideal since, if the seeds happen to retain some moisture, condensation can't escape.
Store the seeds in a cool place away from light. Heat and light will shorten the lifespan.
Not matter how well you store seeds they won't last for ever, so it's best to use fresh seed every year. This is certainly true of onions, parsley, parsnips and some lettuce. Leeks, sweet corn and peppers will generally last two years, beans, broccoli, carrots, spinach and peas three years and anything else four or more years.
Why is cross pollination a problem?
It's only an issue if you intend to save seeds. When bought your seeds came with certain advantageous features, such as an early or late variety or resistance to disease. If different varieties cross pollinate this won't affect the plant's performance or the produce that grows. It will however affect the seeds you save, 'muddying' the features so plants grown from that seed are less predictable in their performance.
Cross pollination can be avoided by isolation, but it's generally too much of a hassle just to avoid spending a couple of pounds on a new packet of seed. I have included guidance below on isolating courgettes, marrows, pumpkins and squashes since the size of the flowers make it easy.
Guidelines
Aubergines: Allow the fruits to mature well past eating stage. Cut open and remove the hard brown seeds. Wash and select those that sink... any floating are poor quality. Lay out on a plate and mix occasionally to ensure they dry evenly.
Beetroot: Since biennial, the plant needs to be left in situ longer than normal to flower in its second year. Once the pods have dried on the plant cut off and shake or rub out the seeds and allow to dry further.
Broad beans, french beans, runner beans: Since cross pollination with surrounding varieties is possible, select plants in the middle of a block of beans. Let the pods mature and dry on the bush until they turn dark brown or yellow and wrinkled, then pick and shell the beans.
Cabbages: A tall flower stalk will grow. It's best to gather the seed pods once they form and start to turn straw coloured and dry, otherwise the pods may shatter and the seed will be lost. Allow them to mature more fully indoors. Once completely dry the seeds can be easily removed.
Chard: See beetroot.
Chillies: Will tend to cross fertilise quite freely. Even if you're only growing one variety anything within 50 metres may contaminate. Best chance is if you grow and mature in a greenhouse. When the seed has fully matured to it's red or green colouring cut open and rub the seeds out onto a plate. Wear gloves to protect your fingers from irritation. Then dry the seeds.
Courgettes: Since these cross fertilise very easily hand pollination is advisable. In the evening identify male and female flowers (female will have small immature fruit at the base, male will not) that will open for the first time the following day and place a rubber band around the petals to stop them opening. The following day remove the rubber bands, remove the petals from the male and brush the male into the female's centre to transfer pollen. Then secure the female petals with the rubber band again. Mark that stem by attaching a piece of string so you know at harvest time which fruit are for seed. Leave to develop and ripen and after harvesting keep in a cool dry place indoors for a month or so to ripen further. Cut the fruit in half and cut out the seeds. Wash clean, spread out on a plate and dry quickly but without excessive heat, for example on a sunny windowsill.
Cucumbers: Since these readily cross pollinate and are fiddly to hand pollinate, only attempt if you're growing in a greenhouse. Allow the fruit to mature well past what would normally be the case, until they're much fatter and have turned dark yellow. After picking keep for about a week to allow further maturing of the seed. Then cut open, scoop out the seeds and follow the fermenting method as for tomatoes to separate the seeds.
Lettuce: Since the seeds ripen gradually, as seed pods form collect matured seeds regularly by shaking into a bag. Seperate from chaff by shaking gently in a sieve. The seeds will fall to the bottom and the chaff can be picked off. Dry the seed further on a plate. Don't save seed from plants that bolt early.
Marrows: See courgettes.
Melons: These readily cross pollinate and are fiddly to hand pollinate, only attempt if you're growing in a greenhouse. When ripe, pick the fruit and keep indoors for a further couple of days to allow to mature further. Then cut open and scoop out the seeds, wash in a sieve under running water and spread on a plate to thoroughly dry.
Peas: Let the peas mature until the pods are brown and the seeds rattle inside. Bring indoors to dry further, shell the peas and allow more drying time.
Peppers: See chillies.
Pumpkins: See courgettes.
Squashes: See courgettes.
Tomatoes: If the jelly like substance coating each seed is not removed early germination may take place, so allow to ripen fully, then slice and squeeze the seeds and juice into a jar. Cover the jar and place in a warm position to allow fermentation to take place. Stir twice a day. Mould will develop and there'll be a nasty smell. After about three days add water and stir well. Good seeds will sink to the bottom. Gently pour away the liquid, empty the good seeds into a sieve and give them a good wash under running water. Tip out onto a plate and dry.
Turnips: These are also biennial and will thus flower in the second year. The seed pods turn from green to straw colour as they dry out. Once almost dried cut the pods off and lay indoors to dry further. Once fully dried the seeds are easily removed.
