Pruning tomato plants

Jenny has previously not had a lot of luck growing tomatoes and wants to know whether she should prune the side shoots that form on tomato stems.

When growing staked tomatoes, it is common practice to prune the small shoots that form in leaf axils because tomato plants do not have strong apical dominance. That means the leading shoot does not contain a lot of the hormone that prevents side shoots from growing. If left to their own devices, tomato plants produce multiple stems that flop onto the ground, producing additional roots from where stems touch soil. In removing the side shoots (by snapping them sideways when small, or cutting with a sharp knife when larger), growth is concentrated in the lead shoot. A second leader can be allowed to form from just below the first bunch of flowers and, once the plant reaches the top of the stake, you can pinch out the tip of the leaders.
This type of cultivation originated in cooler climates to allow more sun to get to the fruit by removing excess foliage, and make weeding easier. Where summers are hot, plants are better left unpruned once the main leaders are established because fruit can become sun scalded, especially where air pollution is low.
Where summers are very hot, tomato plants can do better under light shadecloth (which reduces transpiration) because it is actually warm air that allows tomatoes to ripen, rather than hot sun. As you know, tomatoes that have started to colour can be ripened indoors, although these will be lower in the anti-oxidant lycopene than vine ripened tomatoes.
Removing side shoots will also increase the size of fruit by limiting the amount of fruit that forms. However, other factors are more important in fruit quality. They are: providing a soil pH of around 6.5–7 because tomatoes will develop blossom end rot if they don’t have access to adequate calcium; providing sufficient well-balanced fertiliser such as mature compost, worm castings or poultry based fertiliser; regular deep watering rather than a daily sprinkle; and mulch to reduce fluctuations in soil moisture.
Just another hint: Plastic plant ties can cut into plant stems. When staking tomatoes, use a piece of knit fabric cut across the stretch, instead. Being more flexible, this type of tie won’t damage soft plant tissue.

One thought on “Pruning tomato plants

  1. Can you give me a diagram of a grown tomato plant so that I can see which leaves of the plant need to be pruned. The plants I have growing are just starting to flower and two have just started fruiting.

    thank you,

    Joyce McGopldrick

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