Skip to Content

The Ultimate Tomato Fertilizer Guide

Nobody gets into gardening thinking they just want to grow “okay” quality produce. This is especially true for tomato growers. It’s only natural to want your hard work and dedication to result in big, beautiful, prize-worthy specimens you can show off on social media to the fascination and envy of other growers.

Closeup of healthy, red, ripe tomatoes on the vine.

There’s nothing wrong with that competitive spirit, especially when growing delicious and nutritious foods. However, there are certain things you need to know first before you dig your first spadeful of dirt.

Growing tomatoes isn’t as simple as planting a seed or plant, giving it some water and food, then hoping for the best. Knowing the right kind of fertilizer and when and how to fertilize tomatoes makes all the difference.

This guide will show you how to pick the best fertilizer for your tomato plant, tips on when to fertilize, fertilize, and other useful strategies to help you get the best results for your efforts!

The Different Types of Tomato Fertilizers

There are three basic types of tomato fertilizers, water-soluble, liquid, and granular. Each form offers organic and inorganic fertilizer options. Several factors can impact which type of tomato fertilizer to use, such as weather conditions, plant health, user convenience, and others.

Watering in granular form tomato fertilizer.

Liquid

Liquid fertilizer is concentrated and has to be diluted with water. Along with the common application method that involves applying the liquid fertilizer around the base of the plant, gardeners can also apply weaker solutions (50 percent strength or less) directly onto the plant foliage.

You can apply liquid fertilizer in numerous ways, from a watering can to a calibrated hose sprayer that instantly mixes the liquid fertilizer as the water is discharged.

Liquid fertilizer gives your plant a quick boost of nutrients. However, it has to be reapplied more often than other forms. It also has a long shelf life provided it’s unopened and stored under the proper conditions.

Granular

Granular fertilizer is very easy to apply, stores indefinitely in dry, cool locations and needs no preparation time. Gardners will often apply granular fertilizer by either working it into the garden soil prior to planting or by spreading the fertilizer throughout the root zone of their established plants. These fertilizers are available in both slow and quick-release formulas.

The slow-release formula will break down slowly to provide a steady, long feed that lasts a full growing season. These formulas are available in inorganic and organic products.

As for the quick-release formula, these fertilizers are made using inorganic materials that travel through the soil while being dissolved by water. This formula provides your tomato plants with a quick shot of nutrients.

Person spreading granular form fertilizer around tomatoes.

Water-Soluble

With water-soluble fertilizer, you get the fast-acting attributes of liquid fertilizer combined with the granular’s storage convenience. This means that the nutrients become available immediately once applied to your plants. Like the other types, water-soluble are available in inorganic and organic options.

You can also purchase water-soluble fertilizer in powdered or micro granule form. Both easily dissolve into water. Many gardeners use water-soluble fertilizer the same they would use the liquid version.

Things to Consider When Shopping for Tomato Fertilizer

Every garden is going to be unique. There will always be differences in natural fertility, soil structure, pH, drainage, along with other factors.

This means that there is no all-purpose fertilizer that will give you the best results. It’s also why it’s helpful to have several options on hand to meet the plants’ nutrient needs during different stages of their development. It’s best to think about these factors during your search for the best tomato fertilizer.

Soil Condition

Knowing the condition of your soil is vital to growing the best tomatoes possible. This is why it’s so important to have your soil tested. A detailed soil analysis will show you the current levels of micronutrients and nutrients in your soil. The results also include soil amendment recommendations that will help you rehab your soil into the ideal range.

Every state uses a cooperative extension service that helps both home gardeners and farmers grow their crops. Your state should provide soil testing for a small fee, which is usually $15-$20. Just type the name of your state and “extension service” into your search engine to get started. Results may take several weeks to come back.

A faster way of testing your soil is by buying a DIY soil testing kit. Now, please keep in mind that these tests may not be the most accurate.

Ideally, you should pay for state testing your first year, buy a few DIY tests (which range from $9-$40), and compare the results with the state test to see which kit is the most accurate. Then next year, you can use the DIY kit that works best.

Person holding handful of soil

Content of Chemical Fertilizer

Fertilizer comprises three prime nutrients: nitrogen, phosphorus, and potassium, forming the NPK ratio. Nitrogen is the main element responsible for helping foilage grow. Phosphorous assists flower, root, and fruit development and production. Potassium creates strong stems and assists overall plant health.

Fertilizer manufacturers will prominently display their product’s NPK ratio. One example of a ratio is 4-6-4. The ratio is always in order, with nitrogen representing the first number, phosphorus representing the second, and potassium representing the third. In this case, the fertilizer will have 4 percent nitrogen, 6 percent phosphorus, and 4 percent potassium.

Along with major nutrients, fertilizers can also contain micronutrients, but now always. Micronutrients are usually listed in a less prominent area on the fertilizer package. They often play a small but vital role in different plant processes. For example, tomatoes benefit from the introduction of magnesium, calcium, manganese, sulfur, zinc, copper, and boron.

The Stages of Growth for a Tomato Plant

When your tomato plant first starts its growth cycle, it requires nutrients to support its stem, root, and leaf development. For this stage, a balanced NPK ratio is ideal. You can use a slow-release fertilizer during the planting stage to provide all of the vital major nutrients your plant will need for the growing season.

Person spreading granular fertilizer around tomato plants.

Tomato plants require a small alteration in resources to aid in fruit development, flower production, and disease resistance during and after your plant begins to flower.

Mature plants benefit from reduced nitrogen levels. They also benefit from higher levels of potassium and phosphorus and a few micronutrients. Calcium is highly recommended during this stage as it promotes fruit setting and helps prevent blossom end rot.

Organic Alternatives

Using fertilizers derived from certified all organic ingredients is always an option. However, keep in mind that these formulations will have lower concentrations of NPK. However, they will also have higher levels of micronutrients instead and fewer inorganic materials.

Organic fertilizers are not as likely to damage your plants or cause water solutions should they spill into the local environment.

A pail of organic homemade liquid fertilizer made with comfrey and steer manure.
Organic tomato fertilizer made from comfrey and steer manure.

The majority of organic fertilizers are introduced into plants via microscopic organisms present in the soil, such as bacteria and fungi. These beneficial microbes will consume the fertilizer components and begin releasing nutrient compounds that your plant will then metabolize. And unlike inorganic fertilizers, organic fertilizers support a much broad soil ecology.

Heavy Feeders: A Common Mistake Many Growers Make with Tomatoes

You will hear a lot when it comes to tomatoes that they are “heavy feeders.” While there’s truth to this description, there’s a lot more confusion surrounding what it actually means.

It’s true that heavy feeders take in more nutrients from the surrounding soil than other varieties and require additional nutrients to thrive truly. There are lots of fruits and vegetables that fit into this category.

However, the “heavy feeder” label often leads many gardeners to go a bit crazy with the fertilizer. This practice often ends up hurting their plants more than helping them.

The confusion stems from the term “heavy.” You see, it doesn’t mean “heavy” in terms of applying fertilizer, but rather tomato plants require the soil to be more enriched to reach its full potential.

Clusters of red grape tomatoes on the vine.

Basically, any plant that requires fertilizer more than once within a growing season is considered a “heavy feeder.”

And tomatoes require fertile soil to grow healthy fruits, but adding too much fertilizer can backfire. Excess fertilizer may burn the roots leading to lots of plant growth issues as a result of an imbalance in nutrients. It’s not unlike how taking too many vitamins can make a person sick.

You should give your tomato plants only the amount of fertilizer they need when they need it to keep them healthy and productive.

So what constitutes the right amount and the right time to fertilize tomatoes? Let’s find out.

Best time to fertilize

You only need to fertilize tomatoes during two stages of their growth. The first is just after initial planting, and the second is right before they begin fruiting.

Some folks like first fertilize while they are transplanting their plants to their outdoor gardens. They will either mix the fertilizer with soil or leave it at the bottom of their planting hole.

Person planting young tomato seedling plants.

While this is definitely one option, it may increase the risk of your plant being damaged from too much fertilizer.

One of the most important stages of growth is when tomato plants are transplanted. They often require time to adjust to their new environment. The sudden addition of extra nutrients at this transitional stage may create or worsen a condition known as transplant shock.

Also, depending on the type of fertilizer you employ, the mixture may also burn the fragile roots upon contact.

To reduce this risk, mix some bone meal, compost, or worm castings with your soil at the bottom of your hole. This should give your plants a great start without shocking their system with an overload of nutrients.

Applying a balanced compost may also be more than enough to take care of your plants until it’s time to apply the next fertilizer application.

Also, if your soil isn’t ideal, you can apply the initial round of fertilizer within 30 days of planting. Your plant will still be within the early stages of development, but it should have enough time to adjust and recover from transplanting adequately.

You should apply the second round as soon as you notice your plant starting to fruit. This will give it the boost it will need to grow bigger, healthier fruits before it’s time to harvest.

Tomato blossoms and small green tomatoes on a plant.

However, fertilizing too late in the growing season may cause several issues with your fruits. This is why it’s important to apply the second round of fertilizer early.

How to apply fertilizer to tomato plants

The proper application of fertilizer depends on the type you are using. If you buy a plant from a nursery, it’s very important to follow the instructions closely and never go over the recommended amount.

For liquid fertilizer, you want to pour the diluted mixture into the soil around the base of the plant. But don’t water too close to your stem as it can burn it along with the roots. Water slowly, about an inch from the stem, to prevent any backsplash on your leaves, which can cause damage as well.

To automate this process further, you can use a fertilizer injector to fertilize while you water.

Person pouring liquid fertilizer around tomato plants from a plastic container.

With dry fertilizers, you can sprinkle them on the soil surrounding your plant and gently work them in. Once again, you don’t want to apply fertilizer too close to the stem. An inch or two should be more than enough space without the nutrients being too far from the plant’s roots. Once you’ve worked the fertilizer into the soil, make sure you water deeply and slowly.

But, don’t overwater. You should be able to place your hand into the soil and leave an imprint, but if you notice a lot of water filling up the imprint, you may have watered a bit too much. Overwatering can cause root rot. Tomatoes often need only about an inch or two of water per week.

Nutrients contained in liquid fertilizers will often get washed away when watering. That’s why it’s a good idea to apply it every few weeks after your plant begins to fruit. The frequency and amount of fertilizer during this stage will largely depend on the plant’s health.

Also, it would be best if you always watered tomato plants before fertilizing. If they become slightly underwatered, your plants may consume the nutrients faster than necessary, leading to possible damage.

Watering tomatoes with a watering can.

When to stop using fertilizer

While tomato plants certainly benefit from fertilizer, you want to avoid applying fertilizer too late into the growing season. In other words, as soon as your plant begins to set a large number of fruits and it’s almost time to harvest, you should not apply more fertilizer.

Best Tomato Fertilizers

So now that you know all about tomato fertilizers, which are the best ones to use in your garden?

Best Liquid Fertilizer For Tomatoes

The Miracle-Gro name is well-known among gardeners, so it shouldn’t come as a surprise to see their Liquafeed for Tomatoes, Fruits, and Vegetables in this list. While this is marketed as a plant food, it’s used to add nutrients to the soil so that your tomatoes can make their own food.

Best Water-Soluble Fertilizer For Tomatoes

Greenway Biotech’s Tomato Fertilizer 4-18-38 Powder 100% Water Soluble Plus Micro Nutrients and Trace Minerals comes in as the favorite water-soluble fertilizer for tomatoes.

Best Granular Fertilizer For Tomatoes

Marketed as a plant food and fertilizer, Miracle-Gro Shake ‘N Feed is a crowd favorite for a granular form tomato fertilizer.

Best Organic Fertilizer For Tomatoes

Gardeners overwhelmingly chose Hoss Complete Organic Fertilizer as their top pick for an organic fertilizer for tomatoes.

Best “Easy” Fertilizer For Tomatoes

Sometimes you just don’t want to mess with spreading granules or mixing up liquid forms of fertilizer. You want fast and easy and that’s where Dr. Joe Tomato and Vegetable Bubble comes in. Simply drop a tablet into your watering can and water your plants as normal.

A Home Made Fertilizer For Tomatoes

Maybe you’re not interested in any commercially made products and you want an all-natural option. Here’s a “recipe” for how to make your own tomato fertilizer at home.

How To Make Homemade Tomato Fertilizer

Conclusion

Closeup of healthy, red tomatoes on the vine.

Fertilizing tomatoes is vital for the success of your crop. First, you should understand your soil to know what nutrients your plants need and don’t need. And it’s also important to remember to be careful and apply the right amounts of fertilizer at the right time or risk harming your plant. You can produce an amazing crop you’ll be proud to show off if you grow your tomatoes with care and patience.

To learn even more about tomatoes, click here for our other tomato blog posts.