Growing Tomatoes from Seed – How To Sow

Tips on how to sow tomato seeds and when to pot on seedlings

Growing tomatoes from seed is best done indoors or in a greenhouse if temperatures can be kept in the region where seeds will germinate.

The ideal temperature for germination is around 15 to 21C – the warmer the temperature the quicker the seeds will germinate.

Media for seed germination

It’s good when growing tomatoes from seed to germinate them in small pots or trays of fresh compost. Jiffy pellets, coir, and sponges are also very good alternatives – where one seed is sown in each mini container. It’s more convenient and no soil means less mess or heavy bags of compost to carry!

Media for sowing tomato seeds
Alternatives to seed compost.

Below is a propagator and tray of sponges that are ideal for growing tomatoes and peppers from seed. The shape has been designed to fit on a windowsill. It comes with first feed for seedlings and instructions. If you have enough light on your windowsill, this is an ideal way to start seeds this spring.

Windowsill Propagator and Sponges

Greater choice of varieties

Growing tomato from seed is a little more tricky than buying tomato plug plants or small plants from the garden centre but well worth the effort. The choice of tomato varieties from seed is amazing.

Here’s a link to a selection of Tomato Seed that includes the new Mountain Magic (cherry) blight-buster from T&M. Another variety that is resistant to blight is Crimson Crush (medium large) variety from Suttons.

Tips for growing tomatoes from seed

Always sow in new compost, such as seed and cutting compost, just below the surface and keep in a warm place for the best chance of germination.

It is quite normal for one or two seeds to fail, but if more than 25% fail to come up, there is probably something wrong with the seeds or the way they’ve been sown.

Propagators are best

Sow a few seeds in a small pot or propagator just below surface 1/8 inch or 3mm deep. Place pot in a saucer of water or seed tray /propagator in a large tray to water from below and cover with cling film or lid.

Water from below

The reason for watering from below is so that we won’t disturb the seeds just below the surface, or compact the soil when watering from above.
Another method, if it’s not possible to water from below, is to spray the surface of the compost with water with a hand sprayer.


Keep in a warm place (around 18 – 21C, 65 – 70F) and as soon as the seedlings appear, put them in a light position (not too warm around 15 – 18C) to stop them from becoming too leggy.

propagator for germinating and growing tomatoes from seed

Humidity helps discard seed shells

Using a propagator is best if you are sowing a lot of seeds. The humidity in the lid area also helps the seedlings discard the seed shells as he shells remain soft.

Keeping the seed shell moist will help the seed leaves break out.
Keeping the seed shell moist will help the seed leaves release.

If the seed shells (husks) remain stuck to the seed leaves so that the leaves cannot open, gently wet the shell with a blob of water and hopefully the leaves will open and the shell drop off.

Light and leggy seedlings

Because seedlings need plenty of light to prevent them from becoming leggy, many tomato grower keep their seedlings under lights. See LED Grow Lights

When to pot on seedlings

After their first true leaves are growing, transplant the seedlings into individual small pots so that the seed leaves are just above the soil level (see below).

Compost for potting-on seedlings

John Innes seed compost is ideal for seed germination and JI No.1 is good for transplanting seedlings. It contains the mixture and nutrients suitable for young plants. It’s also a good idea to add a little of the seed compost to the transplant mixture (when the seedlings are transplanted into their own individual pots) as this will help the roots become established.

Other media for germinating tomato seeds

As stated above, there are other different types of media for starting seeds such as Coir (coconut shell), Sponges and Jiffy Pellets to name just three – they are all good!

Avoiding problems

The idea is to grow tomato seedlings so that they develop plenty of leaf growth rather than height. This is achieved by keeping them in a light position without giving them too much water or heat (not above 20c, best around 16-18c) or they will become leggy and not be able to support their own weight.

Over watering seedlings can also cause “damping of” which is a fungal disease that attacks young seedlings

Sowing too early in the season when light levels are low tends to encourage seedlings to become leggy if no extra light is provided.

See Also:

Tips For Tomato Seedlings
Tomato Seed Choice 2019
Feeding Tomato Seedlings