When & How to Fertilize Tomatoes for a Great Harvest

When & How to Fertilize Tomatoes for a Great Harvest

Tomatoes are plants that are known for being heavy feeders. They need lots of nutrients to grow and produce healthy fruit. But it’s a myth to think that just because tomatoes want nutrients in the form of fertilizer, they can be given tons of it at any stage of their growth.

Knowing when and how to fertilize tomato plants is essential so that you don’t give them too much fertilizer or too little of it for their requirements.

Read on to learn everything you need to know about feeding your tomato plants. We’ll look at why it’s important to fertilize tomatoes, when and how you should achieve this, and what types of fertilizer are best.

Should You Fertilize Tomatoes?

Should You Fertilize Tomatoes?

It’s essential to fertilize your tomatoes, and they need to be fed fertilizer at different times of their growth as their food requirements change as they grow. If you fail to give your tomatoes fertilizer, this will cause them to produce fewer tomatoes. 

However, you must follow the correct fertilizer guidelines; otherwise, your tomato plants will also fail to produce a high-quality yield if given too much fertilizer. 

When & How Often Should I Fertilize My Tomato Plants?

When & How Often Should I Fertilize My Tomato Plants?

There are two times when you should fertilize your tomato plants: when you plant them and when they start to produce fruit. However, they can benefit from a fertilizer top-up at other times in their growth. 

Fertilizing Tomatoes When Planting Them 

You should start fertilizing your tomato plants when you initially plant them, as it will give them essential nutrients to help them grow. When digging a hole in the ground to plant your tomatoes, apply fertilizer at the bottom of the hole. Always read the fertilizer’s instructions when applying fertilizer, though, as they might have important guidelines. 

Cover the application of fertilizer with organic matter, such as compost, as this prevents the fertilizer from touching the plant’s roots, which can burn them. It also prevents the tomatoes from getting too many nutrients in one go, which can shock them. 

A slow-release fertilizer is good for your tomato plants during this early stage of growth as it will ensure that the plants will be nourished with nutrients throughout the growing season. 

Note that you don’t need to add fertilizer to the soil when planting tomato seeds because they will germinate without the extra food. 

Fertilizing Tomatoes When They Produce Fruit 

An application of fertilizer when your tomato plants are starting to produce fruit is recommended as it encourages the plants to continue their production and growth. By injecting the fruits with nutrients, you’ll harvest larger tomatoes that are of better quality. 

Fertilizing Tomato Plants When They Produce Flowers

When tomato plants produce flowers, they should be fed fertilizer that contains lots of potassium and nitrogen. Potassium is especially essential because it encourages the production of more flowers on the plant. 

Fertilizing Tomato Plants When They’re Transplanted 

If you have to move your tomato plants to a new site, such as because they’re failing to grow in their current spot, or you want to move them from inside the home to the garden, you should fertilize them.

In the same way that adding fertilizer to your plants when you first plant them is nourishing, giving them some nutrients when you transplant them is a good idea. But do this about three weeks after you’ve transplanted the tomato plants so that they can get used to their new soil and you won’t shock them with too many nutrients. 

At this time, if your soil naturally has enough nitrogen in it, you should add some extra phosphorus to the soil, such as in the form of bone meal. 

Types of Fertilizers to Use

Types of Fertilizers to Use

Your tomato plants require three essential nutrients in fertilizer: nitrogen, phosphorus, and potassium. Fertilizers contain formulas on their packaging that contain three numbers: the first indicates the amount of nitrogen in the product, the second is phosphorus, and the third is potassium.

So, for instance, a balanced fertilizer that has a 10-10-10 formula means that it contains the same amounts of nitrogen, phosphorus, and potassium.

The nutrients you give your tomatoes depend on the growth stage of the plants.

  • When fertilizing plants that are being planted for the first time, you want to give the plants a burst of nitrogen. A fertilizer that contains a 20-10-10 formula is useful. It will help the plants to grow healthy green leaves and boost their general growth. If your soil is already rich in nitrogen, you should only add some phosphorus to it.
  • Before your tomatoes produce flowers, it’s time to use a fertilizer that has more phosphorus, such as one with a 5-15-5 formula. You can also add bone meal to the soil. Phosphorus promotes the growth of blooms.
  • When you can see your tomato plants are growing fruits, you can top up on their fertilizer again. Feed them with a balanced fertilizer that has a 10-10-10 formula. But stop fertilizing your plants when they’re producing a lot of fruit, as this can provide them with too many nutrients that they don’t need.
  • The fertilizer you should add to the soil when transplanting a tomato plant should be a balanced nitrogen or one that’s a bit higher in nitrogen. 

Different types of tomato fertilizer should be applied differently. Here are some examples: 

  • Foliar spray. This is diluted and sprayed onto the tomato plant’s leaves. You should apply this during the morning so that it will evaporate throughout the day and not keep the leaves wet at night, which can promote disease. 
  • Liquid fertilizers. These products should be mixed in water and then applied at the tomato plant base. You don’t want to get them on the leaves, as this encourages fungal diseases. 
  • Granular fertilizer. You should sprinkle this type of fertilizer around the tomato plant base.

There are also organic fertilizers you can use for your tomato plants. These contain certified organic ingredients but lower concentrations of nutrients such as nitrogen, potassium, and phosphorus. This makes them gentler on plants so they don’t burn or damage them. 

Tips for Fertilizing Tomatoes

Tips for Fertilizing Tomatoes

When you’re ready to fertilize your tomatoes, make sure you go the extra mile by following these tips that will enhance your plants’ nutrients and encourage them to grow stronger. 

  • Use compost or other organic matter. Add a few inches (approx. 7cm) of organic matter to the surface of eight inches (20cm) of your tomato plant’s soil before you plant your tomatoes. This is essential to promote better soil drainage, preventing the roots from being flooded with water and nutrients that will suffocate them.
  • Spread the fertilizer instead of applying it too close to the tomato plant. If fertilizer is applied very close to the tomato plants, it can reach the stem and cause burns. You want to spread the product around the plant, about five or so inches (12.7cm) away from the plant base.
  • Water your plants correctly. You must water your tomato plants weekly with approximately two inches (5.08cm) of water. This hydrates your plants and helps the nutrients in the fertilizer to get properly absorbed by the plant. Whenever you water your tomatoes, make sure that you do so slowly at the stem. Deep watering helps the water reach the plant’s roots.
  • If you’re growing tomato plants in pots, you should fertilize them more regularly during the growing season than those in the ground because your potted plants can’t draw nutrients from the soil.
  • Check for signs that you’re giving your tomatoes too much fertilizer. If your plants display symptoms such as yellow or dropping leaves or a lack of flowering, these indicate that you shouldn’t feed your tomato plants too much.
  • Get your soil tested. It’s not always easy to know if your soil is rich in a nutrient, such as nitrogen, which will affect the type of nutrients you feed your plants. Therefore, it’s worth getting your soil tested. Although you can get a DIY test from your local garden center, these aren’t accurate, so getting a professional test from your local county extension office is worth it.
  • Don’t neglect your soil pH. If this is at an incorrect level to promote tomato growth, the fertilizer you use won’t be beneficial. Keep the soil pH between 6.2 and 6.8 for best results. 


You should fertilize your tomato plants regularly to keep them healthy and ensure they get enough nutrients to grow and produce beautiful fruit.

When tomatoes are newly planted, they benefit from a nitrogen-rich fertilizer, while they will benefit from more phosphorus when they’re ready to bloom. 

About The Author

Gina Harper grew up dreaming about farms and growing her own food. She began an urban garden to feed herself and turned it into an incredible hobby. Gina is here to teach you everything from raised beds to container gardening, how to keep plants alive and well in a smoggy city, and the works. It’s time that we carve our own piece of green earth and reap what we sow—she’s here to help you with that.