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Tomato Fertilizers – What Should You Use?

What kind of fertilizer should you use on your tomato plants?  There are so many kinds of fertilizers, it can get your head spinning!  Let’s break it down, though, to see what might be best for where you grow your tomatoes (climate) and how you grown them (in ground or in containers).

What Does N-P-K Stand For?

When you see N-P-K on plant food, it stands for nitrogen (N), phosphorus (P) and potassium (K).  These are the three primary building blocks for all kinds of plants — not just tomatoes.

  • Nitrogen:  promotes growth for the plant vegetation.  In the case of tomatoes, this means the leaves and stems.
  • Phosphorus:  promotes healthy blooms and fruiting.  And you have to have blooms to have tomatoes!
  • Potassium:  promotes healthy root structure, and indirectly helps the fruiting.

Now you know what the letters stand for, what about those numbers?

What’s Your Number?

When you look at a bag or box of fertilizer, you’ll see some numbers, too.  For example, 10-10-10 or 5-8-2 or some other combination of numbers.  These represent the ratio of the nutrients to each other, as well as the strength of the fertilizer.

Say what?  😉

Let’s use the number 5-8-2 as an example.  If you had a spoon and bowl, and plates of nitrogen, phosphorus and potassium in front of you, to make the 5-8-2 you’d do the following:

  • Take 5 spoonfuls of nitrogen
  • Add 8 spoonfuls of phosphorus
  • Finish up with 2 spoonfuls of potassium.

Voila!  You’ve just made a blend of 5-8-2 fertilizer!

Strength, or How High Can You Go?

Now that you know what the three numbers mean with relation to each other, what about their values?  What makes a 5-5-5 different from a 20-20-20?  And isn’t more better?  Read on!

Think of those numbers as being a concentration.  The higher the number, the greater the concentration.  And that has both a good and a bad side.

The good is that when you have a higher concentration, it’s usually in a smaller container, and you add water to dilute it some.  And here’s the problem — if you don’t dilute a high-concentration fertilizer enough, you can burn or (sob) kill your tomato plant!  Think of is as a fertilizer overdose.

It’s sometimes safer to stick with a medium-strength at first, or else dilute the high-concentration fertilizers a little more — at least until you get a handle on what makes your plants happy.

How Often to Fertilize Tomato Plants?

This is kind of a tough one, because in part it depends on how and where you grow your plants.  For example, if you are growing your tomatoes in a sandy soil with little in the way of compost or other soil amendments, you’d want to fertilize more frequently than someone with a rich loamy soil.

Personally, I like to fertilize every two or three weeks, with a half-strength solution if I am using a higher concentration fertilizer.  If I am using something with a low concentration, I might fertilize once a week.  But those are my own rule of thumb — you will have to do some trial and error to find out how often your plants need to be fertilized.

That’s it for now, but there is obviously a lot more to talk about when it comes to tomato fertilizers.  One of the more common questions involves organic versus non-organic types of fertilizer.