Upside down gardening for leggy plants like tomatoes saves space, eliminates weed problems, thwarts most pests and diseases, and promotes better air circulation and sun exposure for your plants. Instead of spending money on a commercial upside down flower pot, make one yourself using a 2 liter plastic bottle.
Using a sharp knife, cut off the bottom of the plastic bottle where it begins to taper. Line up the edge of the cut you just made with tape to prevent the plastic from stretching or breaking after you hang the planter.
Punch four evenly spaced holes through the tape around the container about 1 inch below the edge. Remove the bottle cap and use a sharp knife to poke a few extra drainage holes around the bottle opening.
Choose a young tomato plant with a longer, leggy stem and carefully thread the tip of the plant through the bottle opening. Position the plant with the root ball as close to the top of the container (the bottom of the bottle) as possible, making sure that the first true leaves remain outside the bottle opening. Since your tomato will grow upside down, positioning the root ball near the top gives the roots plenty of room to grow downward.
Fill the container 1 inch from the top with a mixture of potting soil and compost while holding the root ball. Cover the soil with a layer of mulch to prevent the soil from drying out.
Cut two pieces of twine just over twice as long as you want your planter to hang. Thread the first length into one punched hole and out the adjacent one, pulling the ends until they are even. Repeat with the other length and tie all four ends tightly together.
Hang your container in a spot that gets full sunlight. Water your tomato plant whenever the soil surface dries up, probably every day during the warm summer months. Once your tomatoes begin to flower, fertilize the plant with a slightly diluted water-soluble tomato fertilizer during a deep watering every week or two.