Tomato Fertilizer Question: Will this Fertilizer Work for Tomatoes?

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Updated 5.2.24

The Great Tomato Fertilizer Question: how do you know if a particular fertilizer will work well for your tomatoes? Tomato Dirt received this letter from a reader.

Dear Tomato Dirt,
I am an aspiring tomato farmer and would want to produce high quality fruits. I came across a fertilizer labeled 10-12-27. Can I use it to fertilize tomatoes? How many times should this type of fertilizer be applied to tomatoes until maturity?
Maurice Z.
Lilongwe, Malawi

How to know if a particular tomato fertilizer will be useful in the garden

The key is in the numbers.

The fertilizer described (10-12-27) will be helpful to use on tomato plants after they are established in the ground and have begun to flower.

Here's why:

Most fertilizers are a combination of the three nutrients commonly fed to plants: nitrogen, phosphorus, and potassium (referred to as the “N-P-K ratio”).

The three numbers represent those three nutrients.

The first number represents the proportion of nitrogen in the fertilizer. Nitrogen encourages leaf growth (rather than blossoming or fruit development.) In tomatoes, excess leaf growth discourages blossoms and fruit. So the lower number of nitrogen in this fertilizer is a good indicator that it is suitable for tomatoes.

Phosphorus (the second number in the N-P-K ratio) encourages flowering, and therefore fruiting. Obviously this will benefit tomato plants.

Once a tomato plant starts flowering, it needs a higher ratio of potassium for fruit to develop (the third number in the N-P-K ratio). The strong third number in this fertilizer indicates that it will help tomato plants produce healthy, quality fruit!

As for frequency ...

Apply the fertilizer every 3 weeks until frost. 

More on fertilizing tomatoes

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