Prune your tomatoes for maximum size
If you are staking and tying tomatoes, you should also be pruning them. Pruning severity depends on plant vigor, and timing for maximum effect is critical.
June 18, 2014 - Author: Ron Goldy, Michigan State University Extension
When you prune tomatoes you are actually controlling crop load. If tomatoes are not pruned they will have higher numbers and more pounds of fruit, but the overall size will be down. This is not something most growers want. By controlling the number of branches on the plant you are actually reducing the total number of fruit, which results in a greater number of larger fruit.
Michigan State University Extension recommends that tomatoes should be pruned before the suckers are 6 inches long. Up to this stage they are quite tender and can easily be removed by hand-pulling. Prune on a sunny, dry day so the wound dries quickly. Don’t touch the soil, then prune and apply copper soon after pruning to minimize disease spread.
Pruning severity depends on plant vigor. Tomatoes are usually described as low, medium or high vigor. Each category should be pruned slightly different. The reference point for pruning is the first flower cluster, so pruning is not done until that is distinguishable. Find that cluster, and then work down from there. For low vigor varieties, leave the sucker immediately below the flower cluster. For medium vigor, leave two suckers below the flower cluster. For high vigor, leave three suckers below the flower cluster. This will result in two, three and four main shoots on each plant respectively.
Pruning not only increases fruit size but will help with disease control. By removing excess growth, there is more air circulating in the canopy. This helps dry the plant out quicker and aids in spray penetration.