Botanical name (Genus species): Solanum lycopersicum

Planting: What do we need to know before planting for seed production?

Generally you don’t need to think too much before planting tomatoes for seed production. Just choose a variety that you like and that suits your region. Just remember, for seed saving, seeds must be ‘open-pollinated’ or ‘heirloom’. Don’t start with seeds that are marked ‘hybrid’ or ‘F1’.

If you want to be super careful, the only thing we need to know about our tomato variety is whether it is one of the rare varieties with what is technically called an exserted stigma. In this case the flower form allows insects access, to more easily cross-pollinate with other varieties where insects can also access the pollen. This is relatively rare, but it is fairly easy to identify if your variety has this type of flower just by looking closely at the flowers. Check whether the tip of the cone is sealed closed or is open and whether the stigma is sticking out the end or not. If the cone of the flower is completely sealed then you have nothing to worry about. 

Pollination method: Tomatoes are mostly self-pollinated, with some exceptions with visibly open (exserted) flowers. This means that you do not need to do anything to ensure your seed is true-to-type, unless you have one of the rare varieties with open flowers.

Isolation distance: Try and keep the varieties you are saving seed from about 2m from any other tomato variety. Or 15m away if the flowers have stigmas accessible to insects.

Population size: You can get seed from just one plant. It is better practice to grow 5 of that variety and save some seed from each. 

Growing tomatoes for seed is exactly the same as growing for eating. There are no special planting requirements when growing for seed.

Selection: What are we looking for in good seed plants?

We should try not to collect seed from diseased or struggling plants. We want the best fruits from the best plants. We need to ensure that the plant form, leaf type, size, shape and colour of the fruit is what we expect for that variety.

Harvest: How and when do we harvest for seed?

The fruit are harvested when they are completely ripe for eating. The fruit should have a slight ‘give’ to the touch. Fruit should be very ripe but not rotting. Try to collect seed from fruit early in the season as the biggest and best fruit are usually formed then. Later fruit tend to get smaller as the plant heads towards the end of it’s life.

Processing: How do we separate the seed from the plant material?

Fruit should be processed for seed either as soon as they are picked or within a few days. We do not want them to start rotting.

You can just squeeze some seeds out on to kitchen paper, leave them to dry and then store them for next year. This quick and easy method works for many people.

A better method – particularly if you want to share your seeds – is to use a wet fermenting process to remove the gel from around each seed. This removes the germination inhibitor which is in the gel sac so that you get faster germination at planting. It also helps to remove some diseases that might otherwise be carried along with the seed.

To do this, scoop the seed from your tomatoes into a jar and leave it at room temperature for about 24 hours. The advice used to be to ferment for 3 or more days, but recent tests have shown that this can damage some seeds and a shorter time works just as well.

It will start to ferment and a layer of mold may form on the surface. This is OK. Give the jar a stir to physically help the seeds separate from the gel.

Fill the jar with water. The pulp will float and the seeds will sink. Tip off the fermented pulp. You may need to repeat this step until you only have clean seed left in the jar.

Spread the seed out to dry on a tea towel or screen or something similar and move them around occasionally so they don’t stick together.

Leave to dry for about a week, then place in a paper bag or envelope so they can continue to dry.

If you are in a humid climate you may want to look at our video about drying seed.

Storage: What do we need to do to successfully store the seed?

Storing tomato seeds is fairly easy. We just need to make sure they are really dry before sealing them away. We don’t need to worry about pests as none usually lay eggs into tomato seeds.

Like all other seeds, tomato seeds will store best in a sealed container in cool, dark and dry conditions.

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Contributors: Liz Worth, Julie Davies, Arian McVeigh