Does anyone know a tried and tested way of sweetening tomatoes. By that I mean, is there anything I can add to my soil to do so?
I've just planted tomatoes in my garden yesterday.
Good heavens, where do you live? It's winter here, not tomato planting season. Adding tomato food as the trusses form can improve the flavour.
I'm guessing you're not in the UK if you've just planted out your toms.There's noting specific to improve the flavour as far as I'm aware.Seaweed extract watered in now and then will help the plant reach its full potential and planting in a good compost with regular feeding once the first truss has set.
They say not watering them too much improves the flavour - I only water mine twice a week now (unless there is a heatwave and they start to wilt) instead of every day.
The sweetness of a tomato is almost entirely down to its genetic makeup, so you need to grow the right variety. For sweet cherry tomatoes, good varieties are sungold (a yellow coloured one), suncherry premium F1 (red), sweet apertif & sweet millions.
IME, the flavour ( not particularly the sweetness ) of any tom can be improved by not overwatering/feeding.
The variety obviously comes into it as well as Bob says above.