The Best Way to Fertilize Young Tomato Plants – How to Get Your Plants Growing!

For an abundant crop of tasty tomatoes, getting your young plants off to a fast start with fertilizing is essential. But the real secret? It’s all about how, when, and what you use to power your plants early on!

By about Maytime, most of us have already transplanted tomato seedlings into our veggie beds, but they are still young, and this is the time to give them the strength they will need later on, when they grow fruits with fertilizers!

Tomatoes are very hungry (and thirsty) vegetables, and they need lots of food, but when they are young, you need to be very careful… Fertilize them too much, or with the wrong product, and you risk losing that bumper crop you have been dreaming of.

So, let’s see how to fertilize young tomatoes, usually in May, correctly, and boost your harvest later in the season. And even if they are not looking very well now, I’ll show you how to boost them!

Careful – Your Tomatoes Are Still Young!

The Best Way to Fertilize Young Tomato Plants – How to Get Your Plants Growing! 1

When tomatoes are still young, you must be careful about how and how much you fertilize them. And why? True, they need food, but if you give them too much, you encourage early growth. But the sunlight is not strong enough to get them to process all the nutrients, and they can get a bit too tall, but not robust.

Basically, they will grow up looking for the light they need to “digest” all the food you give them.

What’s more, early in the season, they are not yet producing fruits, so we need to be careful with phosphorus. At this stage, you want to boost their stem and leaf growth, so they become strong and well established…

So, there are two mistakes you can make at this stage, with young tomatoes:

  • You fertilize them too much.
  • You give them the wrong NPK.

Well, there’s another mistake, which is that you don’t fertilize them at all… So, we are walking a narrow path at this stage with young tomatoes, and we need to make lots of distinctions.

Slow-Release and Fast-Release Fertilizers with Young Tomatoes

Fertilizers with Young Tomatoes

One big distinction is between slow-release and fast-release fertilizers. If you see that your young tomatoes are still a bit too small, or thin, that they are slow developers, you will need a fast-release, usually liquid product.

Otherwise, you can go ahead with a slow-release fertilizer. And there’s a big difference…

NPK for Young Tomatoes – Slow-Release and Fast-Release Fertilizers

True to what’s written on the tin, slow-release fertilizers feed your tomatoes slowly, of course. Fast-release ones already have all the nutrients available for the roots to absorb, and they are good to give them a big boost.

But here’s the catch. If you are using a slow-release fertilizer, you want a high potassium content, because your tomatoes can use it later on. Or you can use a balanced organic product (like compost) and add some bone meal, for example, to boost the K in NPK.

The ideal NPK for slow-release fertilizers for tomatoes is 6-24-24 or 8-32-16. At this stage, I would stick with the first though.

On the other hand, if you use a fast-release fertilizer… Well, we need to go to the next distinction…

Young Determinate and Indeterminate Tomatoes, and How to Fertilize Them

Indeterminate tomatoes keep growing and they keep fruiting, while determinate ones stop growing, they fruit over a short period of time, and then you can uproot them, we all know that.

But there’s another difference: determinate tomatoes grow faster. And what does it mean when we feed young plants?

It means that if you use a slow-release fertilizer, you are safe, but with a slow-release one…

You want your indeterminate tomatoes to focus on leaf and stem growth at this stage, while you want your determinate ones to start thinking about fruiting.

So, with indeterminate tomatoes, you should use a balanced fast-release fertilizer (10-10-10 or 16-16-16) when they are young. You will move to higher phosphorus concentration next, as soon as you see the first flower buds.

With determinate tomatoes, instead, you should use a fast-release fertilizer with NPK 3-4-6, 4-7-10 or 18-18-21.

Which Fast-Release Fertilizer to Use to Boost Young Determinate Tomatoes?

But which of these three NPKs should you choose, if you want to boost your determinate tomatoes with a fast-release fertilizer? It depends on two factors… How close they are to blooming, and how late they are with their growth.

The smaller they are, they higher the NPK concentration overall you want (like 18-18-21), but if they are a bit underdeveloped but close to blooming, you want a higher phosphorus ratio, so, maybe 4-7-10.

And now you know how to boost “problematic” young tomatoes, let’s see the very best overall fertilizer to feed them at this time!

Your Young Tomato Plants Are Looking Fine? Use This Fertilizer!

If your young tomato plants are fine, you can go ahead with an organic, slow-release fertilizer at this stage. And there are many you can buy off the shelf, but really, you can make your own, and it will give you healthy plants and a bumper crop. Do you want to know how to do it? For every plant, use this “recipe”.

  • One shovelful of compost.
  • One cup of bone meal, or well-rotted chicken manure.
  • Mix them.
  • You can add a spoonful of ash, just make sure it is organic.
  • Lay them on top of the soil, don’t dig it in. Remove and replace the mulch if necessary.
  • Water abundantly.

It’s simple, easy and very cheap. But I know your question…

What about Calcium When I Fertilize My Young Tomatoes?

Tomatoes need a lot of calcium, and they get sick if they don’t have it, especially blossom end rot, which is when the lower part of fruits turns leathery and blackish… Well, let me tell you that our “recipe” is very rich in it!

The Best Way to Fertilize Young Tomato Plants – How to Get Your Plants Growing! 2

In fact, chicken manure has a concentration of calcium between 4.52% and 8.15%, and bone meal between 12% and 13%!

But, very often, the problem is not that there isn’t enough calcium in the soil, but that they cannot absorb it. So, I’ll leave you with a final tip…

Young Tomatoes Need Water to Absorb Calcium from Fertilizers

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Young and old tomatoes drink a lot, and they need water to absorb nutrients in general, but calcium especially. So, very often, the issue is not that there isn’t enough calcium in your soil, but that you haven’t watered them enough, or regularly.

So, as a final tip, water your young and tomatoes regularly, so they can “eat the food” you give them, and then return the favor, when you enjoy a bumper crop!

Adriano Bulla

Written By

Adriano Bulla

After many years as an academic in London, Adriano Bulla became a writer, publishing books like A History of Gardening, Organic Gardening and Elements of Garden Design; he then decided to become a gardener, following his childhood dream, and has been following his dream writing and gardening professionally in Southern Europe, where he has specialized in new and innovative organic gardening fields and techniques, like permaculture, regenerative agriculture, food forests and hydroponics.

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