When to Feed Tomato Plants
Q - My tomato leaves are yellowing but they seem to be producing good fruit, do I need to feed them?
This question we received from a reader is a very good one, because I think many people assume that we always need to feed tomatoes when this is not necessarily the case. There is a big difference between bed and container-grown plants, simply because of the amount of space available for root growth.
Roots that are able to colonise a wide feeding area have access to more nutrients than those restricted to a pot or growbag; this is why container-grown plants will always need to be fed, while those in a bed with plenty of room may not.
There is also a distinction between the older, lower leaves and fresh leaves further up the plant. Old leaves will naturally discolour and often show signs of yellowing between the leaf veins due to magnesium deficiency. This is not a cause for concern. Provided the the rest of the plant looks healthy and is producing good fruit, I would say there is no need to take any action.
If the plant is looking weak and spindly, with all leaves looking yellow/green rather than dark green, then we have a nutrient problem, most likely nitrogen deficiency.
In the video I show an example of a plant that I left too long in a small pot and has run out of feed. You can clearly see the light green upper leaves and yellow lower ones, in contrast to the dark green of the plants in the background.
If your plants look anything like this, you will need to start feeding with an liquid feed every 2 weeks. The reason we need to use a liquid (rather than a slow release feed like a poultry manure pellet) is that liquids have an immediate effect.

Organic Tomato Fertiliser - Better Plants
View ProductTomato feeds are also high in potassium, which promotes flowering and fruit production - so make sure to use a product designed for tomatoes. Personally I like the organic Neudorff range, as they are 100% natural and work just as well, if not better, than the chemical options.
