If you've taken the plunge to using an upside down planter for growing your tomatoes, then you'll need to know how to prune those tomatoes for optimum growth and production. While pruning the tomatoes that are growing upside down isn't difficult, it will help the plant focus on fruit growth rather than using its energy for excess foliage production. With a healthy, well-cared for plant, you should be able to get a good harvest from your tomatoes for the length of your growing season without much effort.
Check your plant weekly as it grows to look for short-side shoots called suckers sticking out at an angle between the main stem of your tomato and a branch. Pinch the suckers off with your fingers or use a knife to remove them as close to their base as possible.
Pinch or cut off the main stem at the tip once it comes to within a foot of your ground level or patio floor to keep the height of your plant under control. Pinch or cut the main stem off just after a branch.
Remove damaged or infected branches from your tomato plant that appear brown and may be drying up by cutting them off at the main stem. Pruning damaged growth will help the plant focus on forming tomatoes rather than struggling to save a dying limb.
Pick your tomatoes as they ripen as much as possible to ensure your plant continues to make new fruit. If a fall frost is predicted, then go ahead and pick all unripe tomatoes and set them in a sunny window indoors to ripen.