The Best Fertilizer for Tomato Plants

The best fertilizer for tomato plants is not what you would think. If you’ve ever gone down the aisle at a garden center, there are a lot of formulations of fertilizers specifically for tomatoes. However, there are only rare instances when the premade fertilizer mixes are the right thing to add to the soil. 

A tomato plant with green tomatoes hanging on the vine.

Let’s dive into the details of what exactly you need for healthy tomato plants that produce loads of delicious tomatoes!

This post contains affiliate links. Full disclosure can be found here.

Test the Soil

The number one most important thing to do before adding ANYTHING to your soil is to test it. I will explain why with a personal story.

When I first started a garden, I would add an all purpose fertilizer to the soil every year. An all purpose fertilizer for a vegetable garden, generally includes equal parts nitrogen, phosphorus, and potassium or NPK. Little did I know, adding an all purpose fertilizer was a huge mistake!

A home garden on a slope with vegetables and an arch.
My garden with too much phosphorus in the soil.

About 3 years into gardening in this location, I decided to send my soil to a professional lab to be tested. When the test came back the phosphorus levels were over 1000 ppm. To put this into perspective, the normal range is 42-68 ppm. I had about 20 times the level that should be present.

Can you have too much of the required nutrients for plants? 

The answer is yes. And to make matters worse, my own ignorance and actions had caused this problem.

Having too much phosphorus in the soil is a major issue. Excessive phosphorus reduces the ability of the plant to take up necessary micronutrients like iron and zinc. 

A soil collection bag filled with soil that is going to be tested in a lab.

It is also water soluble and drains into surface water like streams and lakes causing problems for the water quality and messes with the delicate balance of bacteria present in water.

The only way to correct the problem of excess phosphorus is time and not adding any more!

So this long way of saying I HIGHLY recommend testing your soil prior to adding anything. They make all kinds of tests now and some of them are so easy to do and to read. They take all the work off your plate.

I did an entire article on how to test your soil and what is in my opinion the best all around soil test.

What Necessary Nutrients Do Tomatoes Need to Thrive?

The needed nutrients for  tomatoes are more complicated than meets the eye. Even though a tomato plant can live on only nitrogen, phosphorus, and potassium, it doesn’t thrive unless it has the right balance and levels of the major NPK and micronutrients.

Rows of tomatoes plants in a garden.

This includes micronutrients of zinc, calcium, magnesium, sulfur, boron, copper, iron, and manganese. Tomatoes also need trace minerals.

An example of a tomato grown with all the nutrients it “needs” but still ends up absolutely tasteless is a hydroponically grown tomato. 

If you want tomatoes with out of this world flavor, they need to be grown in soil. They also need to have all the right nutrients mentioned in the right balance.

Is Organic or Conventional Fertilizer Better for Tomatoes?

Research is continually being done on organic fertilizer vs. conventional and the pros and cons of each. Based on my own research, I have the opinion that organic fertilizer is superior in the long run. 

However, you can also do your own deep dive into this and decide for yourself. Conventional also known as synthetic fertilizers go through a manufacturing process. The main benefit is they are inexpensive.

On the other hand, organic fertilizers come directly from plant or animal sources. They also can come from rock minerals.

A tomato plant loaded with flowers at dusk.

Additionally, organic fertilizers often have a wide range of nutrients. For example kelp meal contains potassium but also many trace minerals.

An organic fertilizer feeds beneficial soil microbes, which boost plant health. A conventional fertilizer does not. In fact, research shows synthetic fertilizers have a negative effect on soil biology.

Therefore, the best fertilizer for tomato plants is derived from organic sources and that is what you will find in my recommendations below.

What is the Best Fertilizer for Tomato Plants?

The best fertilizer for tomato plants is one that meets the unique needs of your soil. However, prior to tomatoes being put in the soil, they are started from seed. Let’s dive into seed starting fertilizer first.

A tomato plant filled with green Roma tomatoes.

An important note: Any recommendations of fertilizers in this article come from positive results and personal experience in the garden using them. I link to brands I use, for example, Down to Earth’s Blood Meal. However, other fertilizer companies also make blood meal. Feel free to use any brand you like.

Tomato Fertilizer Mix for Seed Starting

If you start your own seeds in a seed starting mix, fertilizer is essential. Usually a seed starting mix has no soil at all, so what added fertilizers are not based on a soil test.

I have my own seed starting soil block mix recipe. It uses blood meal, bone meal, and kelp meal for fertilizer, in addition to the actual soil medium.

A large storage container that is filled with a homemade seed starting mix.

One thing that really boosts my plants is not just considering the essential nutrients but also the soil biology. I add a soil prebiotic called Ultra to the seed starting mix prior to making soil blocks. 

I add 1 oz Ultra into a container filled with about 10 quarts of seed starting medium. The results are big, beautiful plants that are healthy at transplanting. 

What Tomato Fertilizer to add at Transplanting (An example)

When transplanting tomatoes, they go into the soil of the garden. This is where the soil test becomes important. I will give you an example of what I add to the planting hole of my tomatoes, based on my soil test.

An example of soil test results.

Above you will see the soil test results in the area of the garden where I have tomatoes growing this year. Each nutrient is optimum or above optimum with the exception of boron, which is only just barely below where it should be.

Compost

The first thing to add is compost. Compost will boost organic matter in the soil. Not all compost is created equal or has the same nutrient profile. For the most part compost alone will not supply the tomatoes what they need for additional fertilizer and nutrients. 

An organic compost is being held in hands.

Add 1 inch of compost to the soil surface.

Blood Meal (Nitrogen)

On a soil test, no nitrogen is listed because it disappears so quickly. Nitrogen is definitely necessary for tomato plants so I add this every year. 

To supply the nitrogen the plant needs, in each planting hole I add 2 tablespoons of blood meal and mix it with the soil.

A bag of blood meal fertilizer being poured into a storage container.

Kelp Meal (Potassium and Trace Minerals)

Kelp meal adds a very small amount of potassium. In my soil test, I have enough potassium. So the reason I add this is because it is loaded with trace minerals that tomato plants love!

A small measuring cup filled with kelp meal is being dumped into a planting hole.

The kelp meal will correct the small boron deficiency in my soil. It will also add additional calcium and magnesium which is really important to tomatoes. A fertilizer company had their kelp tested and you can see the results in this kelp meal nutritional analysis.

Kelp meal has close to 60 trace minerals. This equates to healthier plants and delicious flavor!

For the kelp meal, apply at the same rate of 2 tablespoons in each planting hole. 

What about phosphorus?

I add no phosphorus to the tomatoes at planting! My soil test shows my soil has abundant phosphorus and therefore no phosphorus should be added.

I have never added any phosphorus fertilizer to my soil since starting my garden in this location five years ago. For a few years, I added a compost made with chicken manure which naturally added some phosphorus even though I don’t need it.

If your soil does need phosphorus, I recommend bone meal or fish bone meal. Apply at the same rate of 2 tablespoons in each planting hole. 

Soil Biology Booster

In addition to the fertilizers, increasing the beneficial soil microorganisms will help the plants combat stress, reduce disease, and with a stronger plant comes reduced pest pressure as well. 

If you have the time, you can make your own! The JADAM Organic Farming book has recipes for increasing beneficial soil microorganisms.

On the other hand, if you don’t have time to make it from scratch or would rather buy something instead, there are a lot of premade options, probably hundreds!

I personally only have experience with a few. A friend of mine who is a fantastic small farmer told me about Ultra (mentioned above) and that is what I use. 

A hand pumps Agrigro Ultra fertilizer into a watering can.

I add 1 oz of Ultra or about 2 tablespoons per gallon of water and water it into a 300 square foot garden area. A little bit goes a long way and it’s very affordable considering how much coverage you get.

Water this every two weeks.

When to Side Dress Tomato Plants with Additional Fertilizer

After tomatoes have been growing for several weeks, you may need to add additional fertilizer to the plants. If the plants look healthy, likely you will only need to do this once about a month after transplanting.

Again, what you add will be based on what the soil needs. If you have a ton of green growth, dark green leaves, and no tomatoes, that is a sign you have too much nitrogen and shouldn’t add more.

For me, I add one of two options: 

  1. A liquid fertilizer with the soil prebiotic diluted in water
  2. OR ¼ cup blood meal and ¼ kelp meal around each plant.
A liquid fertilizer and soil prebiotic is watered into tomatoes using a watering can.

If you don’t get much rain and you are drip irrigating I don’t recommend adding dry fertilizer. It needs a lot of water to break it down. Instead use a liquid fertilizer. This can be added through a fertigation setup or a watering can.

But if you have an overhead sprinkler, side dressing the plants with a dry fertilizer will work well.

Best Fertilizer for Growing Tomatoes in Pots

The only time I would recommend getting a formulated tomato fertilizer is if you are growing in pots. As you water them throughout the season they lose a lot of nutrients. Since plants grown in pots do not have access to deeper soil and all the minerals, a steady addition of fertilizer is essential.

Green Roma tomatoes hanging on a plant.

Therefore, it is important to be adding fertilizer every few weeks during the entire growing season.

Conclusion

The best fertilizer for tomato plants is an organic formulation. The type of fertilizer added to the soil should be customized based on a soil test.

As a result, it’s better to add single ingredient fertilizers rather than blends. The only exception being if you are growing tomatoes in pots. 

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23 Comments

    1. Thanks for the valuable information. I WILL be getting my garden soil tested next year. I use organic fertilers and pretty much only grow tomatoes/ peppers ,carrots and onions. I occasionally plant beans. It is so time consuming and I believe I have my fungal problem from years past under control. Thanks again ,

    1. The whole article is about how tomato fertilizer should be customized and you should NOT use an all purpose fertilizer like 10-10-10. I wrote a personal story about how I used it and it messed up my soil.

      1. thanks for sharing, not sure what part of the country your in…I’ve been gardening for 40 yrs .i have 150 Sq garden
        during the winter I add my coops clean out pine shavings in all, till it in spring in each hole goes handfull of egg shells compost, bone meal dr earth worm castings and 1 tsp mikos..I never feed my garden again and have more tomatoes I can put up…if I’m lucky I get fish heads to put in the hole…
        just sharing my method…

  1. Using matches from paper matchbooks works amazingly well. Take a full paper matchbook am rip off every paper match. Do NOT strike each match – use them as is. Put the matches all the wau around each main stem of each plant, a little bit away from the stem. This will slowly release the highly needed nutrient of sulfur via water distribution. And because they are made of paper, they are biodegradable. I’ve done this for a couple of years and have had excellent results. I learned this trick from my mother, who learned this from my grandfather who grew a lot of tomatoes on his small farm. You only need to do this a couple of times during the growing season. Cheers!

  2. So I just use miracle grow every two weeks. The miracle grow that is recommended for tomatoes and it seems like I get the best results, but I love to read how other people are growing their tomatoes.

  3. The best luck every time for me was cow manure I had the best tasting tomatoes ever, I swear by it never let me down!

  4. I wanted to leave you some ideas for your Egyptian Walking Onions, but was not sure where was best to post, so trying to add to the latest post on your blog I could find.

    I got my walking onions about 20 years ago from a 4th generation German farmer. He just liked them but did not use them much. Over the years I have done what you do and added the bigger tops to cooking and canning. Last season on a whim I put my bulbs, with the bulbetts removed but left the major part of the stalk attached, on a well ventilated tray that was on a stump under a blue spruce tree. After two weeks the sweet yummy part of the bulb doubled in size and the woody stock side shriveled slightly making it easy to separate them. Stalks go to the compost pile and bulbs to the kitchen. Email me if you want pictures of how this goes. bonnie at enhanced equine dot com.

  5. My grandfather was an organic gardener and grew an amazing crop of tomatoes
    He akways said for best results
    when transfering young plants to soil pull off a few branches of the plant and plant them DEEP to promote a rich root base to the plant
    what a difference this makes

  6. This is great information, Becky. Thank you so much! I’m brand new to growing my own produce and after 2 years, I just can’t seem to get anything to grow well in my raised beds. (I live in northeast Arkansas).
    My biggest problem with tomatoes is that they grow a little bit, but then never get bigger, and when I remove them from the plant, they never ripen.
    Next year, I’ll use this info to prepare the beds earlier, and then do a lot of praying! 😉

    1. Thank you! That is so interesting your tomatoes are doing that. I hope the implementing the info solves your problems!

  7. interesting reading.
    we use a really simple and free fertilizer. we put nettles in half a buket, fill it with water and let it stand for about two weeks. then we take out the nettles and bottle it up. put it in a cool place, it is a good starter when the plant is growing and is good for the roots.
    about 3 to 5 ml/ litre is good for small plants. a bit more for bigger ones. It is a fantastic fertilizer, you can spray it on the plant if cloudy. It keeps a lot of pest away. and then I use as a complement the grass from moving the lawn. a couple of time and especially on greens and squash.
    Thank you for the tip of checking the soil..

    If you for example eat dried nettles you just need 1 to 2 tsp. and you got like a multivitamin pill. so I guess the plants get a lot of good stuff.

    I actually started to eat nettle everyday about 7 years ago for the vitamins and minirals and my PMS is never bothering me since. just if I forget the nettles.

    1. How interesting about nettles relieving your PMS, pharmaceuticals/science seem to rely on the pill for everything to do with women’s health. Our forgotten natural methods need to be reintroduced.