The leaves of tomato plants can become yellow for a number of reasons, including nutrition. According to Masabni, “nitrogen is the most prevalent cause,” and the reason for this is that people typically do not fertilize tomatoes sufficiently. According to him, tomatoes are heavy feeders, which means the plant takes twice as much fertilizer as a cucumber does and even four times as much as beans do.
- This is because tomatoes have a larger root system than cucumbers do.
- If you do not provide the plant with a sufficient amount of nitrogen through fertilization, the older leaves may begin to turn yellow and, in many instances, may fall off.
- The reason for the yellowing of the older leaves is that they are passing on their nitrogen to the younger ones, which allows the younger leaves to continue living.
The yellowing of leaves can also be the consequence of a lack of iron in the plant, however this symptom will be most noticeable in the leaves that are the most recent to emerge from the plant. However, a magnesium deficit can cause yellowing on the older leaves that appears more like speckles or spots than it does yellowing.
According to Masabni, “these three, nitrogen, iron, and magnesium, are the most prevalent nutrient shortages producers should pay attention to and fertilize regularly for.” It is important to bear in mind that if a significant amount of fertilizer is applied to the plant, the plant will also demand a significant amount of water.
“There is no exact formula for how much water your tomato may require, but a good rule of thumb is to conduct a moisture test where you insert your finger several inches down in the soil to test for moisture around the roots,” he added. “This will give you a fair idea of how much water your tomato may need.” “It is time to water if it seems dry, and as the tomato plants get closer to reaching full maturity, they will demand an increasing amount of water.
Should I remove the yellow leaves from my tomato plants?
QUESTION: Should I remove any leaves that have turned yellow on the tomato plants? ANSWER: When your tomato plants reach a height of around 12 to 18 inches, you may notice that some of the leaves below the initial set of blossoms have begun to turn yellow or die.
- This is a normal part of the maturation process.
- As long as the dead or yellowing foliage is located below the first set of blooms, it is OK to remove it from any tomato kinds.
- There is no benefit to be gained by removing dead or yellowing leaves, sometimes known as “suckers,” that grow any higher on the plant when working with determinate variety of tomatoes.
(As long as they aren’t taller than the first set of blooms, the “suckers” that develop from where a branch meets the main stem on determinate tomato plants can be removed if you so want.) You are free to remove any and all suckers from indeterminate tomato plants, provided that the suckers are not so huge that doing so would cause a wound that would be detrimental to the plant.
Tomatoes of the indeterminate variety may benefit from the removal of yellowing or dead leaves at all heights, as well as from additional overall pruning in comparison to determinate kinds. Because determinate tomato plants only bloom and produce fruit once, there is a predetermined maximum number of tomatoes that may be harvested from each plant.
This maximum number is not significantly affected by trimming. The benefits of pruning are maximized with indeterminate types, which bloom and set fruit many times during the course of a single season. 
How do you add nitrogen to tomato plants?
Nitrogen: In order to provide a gradual release of nitrogen to my tomato plants, I either use one cup of old coffee grounds or two cups of alfalfa pellets. Before you add the pellets to your mix, you need to make sure that you give them enough water so that they may be broken up into smaller pieces.
You can take blood meal if you require a greater increase in the amount of nitrogen in your diet. Include a half cup of it in your mixture. You may also include finely chopped human hair or pet hair to your mixture, despite the fact that this might seem unusual. Tomatoes are able to make good use of the protein keratin, which is produced when hair is broken down and added to the soil.
This also contributes nitrogen. 
