First know what type of plant you’ve got: Determinate (Bush) or Indeterminate (Vine). The Indeterminate varieties grow up and tall are ‘vining’ and require staking, each plant with its own individual tall stake or each plant strung to a top beam and supporting structure. This type of tomato plant requires more pruning attention, about weekly, and the tomatoes ripen gradually. Whereas the Determinate (Bush) size you don’t want to prune any part of the plant off unless for maintaining ventilation and sun exposure to your tomatoes. This tomato plant will  remain more compact and the tomoto fruit will ripen at the same time. These plants are usually bushier and you could take any heavy branches. They also benefit from a string fence to keep the branches contained.
But to keep things ventilated to prevent contracting disease, starting off with adequate spacing between plants is vital, move or remove plants if they are planted less than 2′ apart. As you trim off infected plant parts, don’t put it in your compost. Don’t be afraid of taking off those leaves and branches for ventilation. Also when transplanting tomatoes into the ground, make your hole bigger to accommodate compost and organic fertilizer mix as well as burying part of the stem for extra root growth.
It seems to me that almost every gardener in Canada has grown or will attempt to grow tomatoes each year. A popular ‘fruit’ in our Canadian and international gardens, it is widely used by people of various cultural backgrounds. Growing tomatoes, if you’re serious about it, takes care and attention, but they will also survive without any pruning too if you choose the Bush Variety. Hot weather and dry summers are the best conditions, regular watering during growth will prevent Blossom End Rot.
Cutting off the flowers in August – Tomatoes are susceptible to a late blight fungus if they’re either in too humid conditions (under plastic cover) or in the rain with wet leaves. Since the summer rains start in August here on the coast, most plants won’t survive for much longer before they are infected, so better to let the plants focus on turning their green tomatoes red packing lots of flavour! Here is the science behind it here. You can let partially ripened tomatoes ripen off the vine if you need to avoid fungus infection in rainy weather.
