Plants have three basic components; roots, stems and leaves. I grow some of my tomatoes in plastic planters that have open bottoms.
Tomatoes are able to grow roots along the stems. Some people let the stem get leggy and then lay the stem down in a horizontal position to allow more absorption of water and nutrients through the the increase in area. If you are growing in a planter, you may want to consider placing the young plant close to the bottom of the container. As the plant grows and reaches for the sun, add soil around the stem. In a short time, small roots will appear along the stem that are buried in the soil mix. Those roots will increase the absorption factor for the plant. The size of the planter that you use will help determine the root growth. A planter that is too small will reduce root development.
For early tomato growth, I put a used five gallon water jug over the plant to allow in sunlight but to keep the plants warm at night. The jug also reduces evaporation of water. Then I added drip irrigation using a 2 liter tonic bottle to drip compost tea.
Container planting provides flexibility for people planting in limited spaces. Good times.