A trellis could work very well with tomatoes. When I ran a hydroponic store I sold tons of tomato net trellises. My Father liked to use these cages/braces that encircle each plant, but I like trellis more. A trellis does take more work.
"Topping" the plant to keep it a reasonable height is also a good idea.
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o-|-o <---Imagine this is a normal tomato plant. It has one stem and it goes up. The o's are tomatoes. The bars are stems.
If you cut the top of the plant off, the bottom branches will turn into the main branches, giving you multiple tops. You could make a plant look like this.
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\/ Cutting the top of a plant off forces it to grow in a new shape, and instead of growing straight up like a tree and bearing fruit, a plant can be forced to grow into a bush shape instead. Not only is the plant easier to manage, but yield should be improved as well. [The reason for the yield change has to do with how much easier the plant has it to pull water up to its top leaves. A 3' tall plant works a lot less hard than a 6' tall plant needs to to drink the same amount of water. The energy not used by the plant pulling water goes to making larger, tastier fruits.]
Another benefit of a shorter plant is: more solar power taken in from the leaves can go to the roots... roots are the #1 most important thing with most plants.
My vote is to cut the plants tops off to manage its height. Tomato cages or staking may be required as well as yield increases in the later weeks.
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When you transplant your plants into the ground, cut off the bottom set of leaves and apply some Rootone or Hormex rooting powder to the wound [Walmart should carry these products, if not a local gardening store will, these are not expensive items]... then try planting the root ball sideways with the stem near vertical to the ground. The wound should transform into another set of additional roots. The existing roots will also benefit [increase in size] from reorienting themselves... this bit of stress produces a much more superior root system than planting the plants normally. Again, roots are the most important thing. Root mass dictates yield.
If you try the sideways planting a bush like plant may emerge w/o the need to cut the tops off of plants.
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/\ <--This would be an example of what happens when you plant a plant sideways. The main stem is made to function like a vine, and stalks emerge from the vine-like stem, each of these emerging stalks could be treated as an individual plant if one wanted to trellis it out over some space. If a plant gets too talk or lanky, turn it sideways!
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http://gardening.about.com/od/totallytomatoes/qt/Red_Mulch.htm^If you live in a cold area, you can prepare the area you will be planting tomatoes by warming it up with red mulch or black plastic for a more harmonious transplant.
http://gardening.about.com/od/growingtips/tp/Tomato_Tips.htm^I can vouch these tips are effective as rules of thumb.
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What variety of tomatoes are you doing this year?