Feeding tomatoes is a subject that will start a discussion where no two tomato growers will agree! However, there are general principles that will normally produce good results. The rest comes from experience!
Amount of Food
Tomato plants need very little food when they are seedlings, but when they are mature plants and bearing fruit, they require a lot of food (nutrients).
Types of Food – Mineral Nutrients
We also give them nutrients of a different kind when they are young plants than when they are mature and fruiting.
We hear a lot about giving calcium to older plants to avoid blossom end rot, but small seedlings need calcium too for strong cell growth.
Macro Nutrients – NPK
Generally, a balanced feed of Nitrogen, Phosphorus and Potassium (NPK) is given up to fruiting. Then a boost of phosphorus and especially potassium for fruit growth as soon as the small tomatoes appear.
These three nutrients “NPK” are known as macro nutrients.
Other mineral nutrients known as micro nutrients are also given in smaller quantities. However, if you have really good quality soil/compost, many of these micro nutrients should be available already in the soil.
There are issues that can sometimes occur, when one nutrient blocks another. This usually happens when tomatoes are over fed and there is too much feed in the soil.
When we are given tips about growing tomatoes such as “tomatoes are heavy feeders” or “tomato plants like lots of water” the first thing to be aware of is that each of these bits of advice is both right and wrong – depending on the stage of growth that our plants are at.
Tomato plants are heavy feeders when they are fruiting and they do need lots of water when they have a lot of leaf area to supply water to.
The opposite it true when they are seedlings and young plants. Too much food and too much water can cause many different problems – it’s sometimes a case of “killing our plants with kindness”.
So little and often, and less is more … both of these are good sayings to follow for feeding tomatoes correctly.