This means that feeding tomatoes isn't really necessary until the flowers have set and small the small fruit start to grow.
One of the mistakes that people who are new to growing tomatoes make is to give give small plants tomato food. This is only necessary for tomato plants when they are fruiting, feeding young plants a full strength dose of tomato food can sometimes cause root damage.
These are some of the ways I would feed my small plants, and plants not yet fruiting.
- General purpose plant food at half strength.
- Liquid seaweed extract
- An organic stimulant or tonic such as SB Plant Invigorator
Other nutrients that are sometimes used are epsom salts (magnesium sulphate) and extra calcium (to help prevent blossom end rot). Both of these "extras" may be given as a foliar feed to boost a plants intake of a particular nutrient, usually because of signs of a deficiency. The problem is however, as soon as symptoms appear in tomato plants, it is often too late to make much difference.
Don't get too concerned with feeding tomato plants because if you do, you'll probably kill them with kindness and give them too much.
To Sum Up
If plants have been transplanted into new compost - within the last four or five weeks - they do not need to be fed.
However, when transplanting, a half strength feed of general purpose food is helpful (but not essential) because it helps the plants become established in their new home.
Give tomato food (only) when plants start to fruit - little and often is the best way. Professional growers usually feed at every watering, at a reduced strength, so plants always have access to food as they need it.