Installing support while a tomato plant is young is easier on the roots and stem. A stake should be close enough to guide growth but far enough away to avoid piercing the main root zone.
Choose the support
Use a sturdy stake long enough for the mature plant and smooth enough not to cut the stem. Place it before the root ball becomes dense around the plant.
Drive it carefully
Set the stake several inches from the stem and push it into firm soil. Avoid hammering directly beside the crown.
Tie loosely
Use soft ties and make a figure-eight between plant and stake. Leave room for stem thickening and add ties as the plant grows.
Inspect after wind
Check for rubbing, leaning, or a tie cutting into the stem. Adjust support rather than pulling a bent plant upright abruptly.