Apply a liquid fertilizer mix with a higher ratio of phosphorous and potassium around the base of the plant two to three weeks after your tomato plant begins to grow fruit. Water for 15 - 30 seconds after.
Once fruit begin to grow larger, reduce the liquid fertilizer application to once a month. If leaves are yellow or fruit remain small, apply fertilizer every week until growth improves.
At the end of the growing season, reduce the liquid fertilizer mix to every 6 weeks if healthy tomatoes remain on the plant. If the plant is not healthy, leaves are wilting, or end of the season rot begins to form on tomatoes then apply the liquid fertilizer mix weekly until you pull the tomato plants out of the ground.