Personally I do not grow the Cordon varieties of tomatoes outdoors, I prefer to grow the bush varieties outdoors as they need much more ground space. Now this is my personal preference which works for me and my available space and climate, it is NOT a hard and fast rule i.e. if you do not have a greenhouse and or only have limited space outdoors then by all means grow cordon varieties, like wise if the general climate in your area does not support growing tomatoes outdoors then if you like them grow bush varieties indoors.
Like so many things in gardening you need to find what works best for you, you do not have to follow exactly what I am saying because I have based this on what works for me and tried to expand to what will work elsewhere.
Cherry / Dwarf Bush varieties of tomato
Now these were breed to be grown in hanging baskets or pots, so this is exactly what we do. Once the roots are just appearing out of the bottom of the pot I transplant to either a hanging basket or 12inch pot.. I fill the container with standard potting compost mixed with water crystals (these help to keep the compost moist) and transplant one plant per container, using the "part fill/make hole/plant then fill" method described in the section on growing from seeds. I also put in a couple of companion plants such as tagetes or lobilia which help to deter pests etc.
At this stage I keep an eye on the weather and if a cold night is imminent I move the plants indoors for the night, or if more practical I cover with fleece. By the end of May this not usually required and the only task needed is a weekly feed. Oops did I forget to mention that very regular watering is also needed. Then all that is left to do is pick the ripe tomatoes as and when needed. Believe me nothing tastes better than a freshly picked tomato eaten straight from the vine. Whoops sorry you really should wash them first as even though you won't have used anything nasty on them (will you?) you never know what is in the rain or what your neighbours have been spraying may have drifted in on the wind.
Main Bush Tomato Varieties
The ideal location for growing tomatoes outdoors is a sunny, well sheltered site, which is a rare combination to have unless you have access to a Victorian walled garden. The soil needs to be well cultivated and rich, a dressing of well rotted manure in the previous autumn helps. On sandy based soils dig a trench and line it with newspaper then fill with compost. This will ensure a supply of water is available to the plants. It does not remove your responsibility of regular watering. On clay based soils this is not necessary as the clay will hold the water.
A couple of weeks before planting out I clear the ground of weeds and dig over then level off. Once this is done a cover with a weed suppressant fabric, this has three main benefits, It sops the weeds growing meaning less work for mean and more importantly more nutrients for the plants, it warms the soil up and then helps maintain an even soil temperature and finally it prevents slugs as the fabric stops them disappearing into the ground during the day.
When the plants are ready to plant out, i.e. the first flowers are open, I plant in the middle of the fabric about 2 ½ feet apart, again planting deep to encourage root growth. In between the tomato plants I grow tagetes which are well know to deter that most common of tomato pests white fly. Once Planted I cover with a cloche which I leave in place until the end of May, this keeps the plants warm and protects from the chance of a late frost.