In the UK, growing tomatoes from seed is very straight forward start off by sowing your tomato seeds between late February and early March (a little later in more Northern parts). Using 2½ inch pots and standard potting compost, sow the seed thinly and cover lightly with compost. Now unless you are growing for the neighbourhood be careful how many seeds you sow. If growing a Cordon variety an average family will need 4 or 5 plants.
Personally I sow 10 to 12 seeds, this allows for low germination, damping off (see pests and diseases) and usually gives me five goods plants to use a couple to give away. Obviously you can adjust these numbers to suit your own needs. If kept in a cool, dry and dark environment the seeds in an open packet will keep for another two years. The older the seed the more I sow as germination failure increases with the age of the seed.
Sowing tomato seeds earlier than late February (in the UK) is rarely beneficial as the days are too short and the weak light intensity gives rise to weak spindly seedlings which have been drawn to what light there is. It is there fore much more satisfactory to sow a bit later and get good strong seedlings. In my experience these later sown seed tend to catch up and even over take earlier sown ones. Sometimes though even late sown seed will give weak drawn seedlings, these can be rescued to some extent by planting deeper in the soil when transplanting, (see potting on)
After sowing put the pots into a heated propagator or on a warm windowsill or warm cupboard. I am fortunate that my kitchen window faces due south so I can use this without needing a heated propagator, it does of course cause a few issues as to what should be on a kitchen windowsill.
Potting On the Tomato Seedlings
Moving on the tomato seedlings from their original seed pot to their final location is generally a three stage process, but if growing a particular vigorous variety then an additional stage will be required.
Once the tomato seedlings are about an inch tall I transplant them into individual modules in a seed tray and then place them in the greenhouse. If you do not have a greenhouse or your climate is still too cold you can transplant into 1inch pots and place on a warm windowsill. I generally transplant “Deep” which encourages root growth and can rescue drawn weak seedlings.
To transplant fill the seed tray modules or pots with standard potting compost. Make a hole in the compost wide enough to get the seedling roots into without damage and deep enough to ensure all the roots are below the surface of the compost. If planting “Deep” the hole should be deep enough to take the roots and half of the stalk. Gently firm the compost around the seedlings and water well. Do not let the compost dry out but do not over water as this can lead to damping off, (see pests and diseases).
When the seedlings have outgrown the modules it is time to transplant into 3 inch pots. Select the strongest plants, the number you want to select is the number of plants you finally want to end up with plus an extra 25% to give you a choice at the next stage. The method of transplanting is similar to before. Fill the pot with standard potting compost and make a hole in it, this time the hole should be large enough to take the whole module plus some extra depth if deep planting. The easiest way to do this is the "part fill/make hole/plant then fill" method, fill the pot to within half an inch of the top and then push an empty module into the compost to form the hole. Remove a seedling from its module and place into the hole and then gently fill the rest of the pot with compost to just below the rim. (return to outdoor), (return to inside) Repeat for the other seedlings and water well. Again do not allow to dry out.
Tomato Seeds - Ailsa Graig
available from "Suttons Seeds"
This is only needed if growing a vigorous variety and is a repeat of stage three but using 4 inch pots.
This is where we move the now developed plants to their final location and the way this is done depends on type, variety and whether it is indoors or outdoors. Growing Tomatoes Outdoors, or growing tomatoes inside.