How to Fertilize Tomato Plants for the BEST Harvest Ever!

If you want a HUGE tomato harvest, one of the best tips I have is to learn how to fertilize tomato plants the right way.

Tomato plants are one of the heaviest feeders in your garden, so they require a lot of fertilizer to get through the growing season. If you want the best results and harvest from your plants, you have to learn how to fertilize tomato plants the right way.

Don’t worry; fertilizing tomato plants is easier than you may think, and it’s often the secret to great tomato plants.

No, it’s not simply just giving some fertilizer and hoping it works for your plants. You need a routine that provides the plants exactly what they need at the stage of growth they are in. Gardeners need to understand the basic fertilizing requirements so your plants get exactly what they need.

Let’s take a look!

Related: Warning! Here is Why You Have Holes in Tomatoes

Are Tomato Plants Heavy Feeders?

Tomato plants are heavy feeders, but this leads to confusion. These plants draw more nutrients out of the soil than a lot of other vegetable plants, and those nutrients help the plants thrive.

However, the problem with calling any plant heavy feeders is that it causes gardeners to apply more fertilizer than needed. This causes harm more than helping the plants.

Heavy feeders doesn’t necessarily mean you need “heavy” applications but you will need to enrich the soil more at planting time and apply several extra applications throughout the growing season. However, that doesn’t mean the applications should ever be more than recommended.

Remember, too much fertilizer will burn the roots, leading to problems as a result of a nutritional imbalance. That’s not what you want when you fertilize tomato plants.

What is the Best Fertilizer for Tomato Plants?

Whatever fertilizer you pick for tomato plants contains the main macronutrients, such as nitrogen, phosphorus, and potassium, and essential micronutrients, like calcium, magnesium, zinc, and boron. Tomatoes require different ratios of these nutrients during different stages of the growth cycle.

Unfortunately, there is no one single tomato fertilizer that works for all gardens and all stages of growth. You need to focus on apply what the plants need at each stage.

Here are the nutrients a tomato plant requires.

  • Nitrogen: This nutrient helps with the growth and care of the foliage; it’s one of the main nutrients needed at the start of the growing season. However, too much nitrogen leads to bushy plants with little or no fruits.
  • Phosphorus: This nutrient is crucial for the growth and development of the root system, so your plants need it to fruit as well. So, this is needed for the initial stage and final stage of growth.
  • Potassium: This nutrient grows plants rapidly, producing flowers and fruits. It also helps with tolerance to diseases and developing photosynthesis.
  • Calcium: All plants need to have calcium for proper leaf and root growth, and they help to produce a firm tomato. If your soil lacks calcium, it also may lead to blossom end rot.
  • Magnesium: Another nutrient these plants require is magnesium, which helps the plant stay green and improves fruit quality and the overall flowering of the plant.
  • Boron & Zinc: These micronutrients help with flowering and ripening of the fruit.

When to Fertilizer Tomato Plants

Unlike other plants, tomatoes benefit from fertilizing differently at different key points of their life. The plants need specific nutrients as they grow throughout the season, so you don’t want to use the same fertilizer all the time.

There are three times when you need to fertilize tomato plants: as tomato seedlings, when you transplant into the garden, and when they grow and start to flower.

Here is a simple chart to remember!

Starting SeedsTomato SeedlingsDuring GrowthFlowering & Fruiting
Nutrients RequiredThe seeds provide all the nutrients required. NPK for foliage, root, and plant growth.Phosphorus to help with root growth and nitrogen for foliage growth (but less than before)Potassium and phosphorous, this is when to decrease nitrogen.

Fertilizing Tomato Seedlings

After you start your tomato seeds, it’s a great idea to fertilize lightly from the start. It encourages the best growth of your tomato seedlings.

It’s easy to fertilize tomato seedlings. Try adding worm castings or a slow-release, balanced organic fertilizer to the seed starting mix after the seeds sprout.

If you purchase tomato seedlings from a local greenhouse, chances are the nursery already fertilized them. So, give them a low dose of fertilizer when you bring them home before planting.

Related: 5 Reasons for Purple Stems on Tomato Seedlings

Fertilizing When Transplanting

Before planting, it’s a wise idea to add compost to the soil, but you should also apply a slow-release fertilizer when it’s planting time. During the first four to eight weeks in the ground, tomato plants require a steady dirt to build a strong root structure.

You have a few ways to do this besides adding compost to each hole.

I always add eggshells to the hole and Epsom salt, but a slow-release, well-balanced fertilizer works. I like tomato plant fertilizer spikes as well; you put two beside each tomato plant and they add a steady dose of nutrients throughout the growing season.

Fertilizing As Tomato Plants Grow

After transplanting, tomato plants need plenty of nutrients to continue to grow. Transplant shock is real, and it is hard on plants. After tomato plants are in the ground for three to four weeks, it’s time to start fertilizing again since they are established and ready to start growing.

Nutrients should be added to the plants in a slow method because adding too much fertilizer all at one time creates significant issues. The last thing you want to do is burn and damage plants, but it also leads to your plant overproducing leaves without any blooms and fruits.

Aside from adding compost or worm casting to the plants, adding a liquid organic fertilizer is an excellent option. Use the fertilizer at half the recommended strength every two weeks to give a slow and steady supply of nutrients.

One thing to know is if you are growing indeterminate tomato plants rather than determinate tomato plants, there is no clear distinction between fruiting phases. So, you need to provide constant fertilization with a 8-32-16 or 6-24-24 fertilizer.

Related: The Crazy Truth about Indeterminate and Determinate Tomatoes

When to Stop Fertilizing

Tomato plants may be heavy feeders, but adding too many nutrients is often a problem. So, you want to avoid over-fertilizing too late in the growing season.

Once your plants set a large portion of fruits and harvesting begins regularly, it’s safe to stop fertilizing. Adding too much fertilizer at this point in the growing season causes the plant to stop producing blooms; the plant may decide to grow more foliage instead.

Always remember to pick your ripe fruit daily because this helps send nutrients towards helping new fruit grow and develop.

How to Fertilize Tomato Plants for a Large Harvest

Add Compost to Your Soil Before Planting

Adding compost or well-rotted manure to the top of the soil at planting time is highly recommended; it’s one of the best ways to give your tomato plants (and all of your veggie plants) what they need to grow.

Compost is truly gold when it comes to the health of your plants, and it contains nitrogen, a nutrient all plants need, especially tomatoes. Adding four to six inches of compost to the top of your garden beds is always a fantastic idea!

Related: 15 Composting Tips for Beginners You Need to Get Started

Start Your Seedlings & Fertilize

If you start tomato seeds at home, the seedlings need to be fertilized once sprouted. These seedlings grow fast in the right growing conditions.

Grab a general, all-purpose vegetable fertilizer – I like the Jobe’s Organic Vegetable & Tomato Fertilizer – and follow the directions. If the package doesn’t tell you how to fertilize seedlings, make sure you dilute or reduce the amount greatly to only a teaspoon or more of fertilizer.

Add Phosphorus When Transplanting Tomato Seedlings

Tomato plants hit quite a growth spurt after they are planted into your garden, and they need lots of nutrients to make it through it. If you added compost ahead of time, your plants are more than likely sufficient, but consider adding a small dose of a phosphorus fertilizer when you fertilize tomato plants.

All plants need nutrients when you transplant them into your garden beds. Tomato plants need nitrogen and phosphorus at this time the most. Using a combination of fertilizer spikes and bone meal give your plants the nutrients they need when transplanting tomato seedlings.

Bone Meal

Bone meal is an excellent fertilizer, but it is an animal product so if you prefer vegan fertilizers, this wouldn’t be for you. This fertilizer provides sufficient phosphorus, which is what seedlings need to grow strong roots and encourage fruiting.

Bone meal is made up of ground animal bones; companies typically use beef or fish bones (or any other animal bones). Most bone meal products have a ratio of 3-15-0, and the calcium in this fertilizer also helps to prevent tomato blossom end rot, a common tomato problems.

I have tried several bone meal products in my garden.

Bone meal is a slow-release fertilizer, and it takes anywhere from eight weeks to four months to break down completely in the soil. Always follow the directions on the back of the container.

Fertilizer Spikes

One of my favorite tomato growing essentials in the Jobe’s Organic Fertilizer Spikes with an 6-18-6 NPK ratio.

Place the fertilizer spikes three to six inches away from the stem after transplanting the seedlings into the ground. Spacing is even more essential when you grow tomatoes in a container.

Fertilizer spikes last around eight weeks before they deplete into the soil.

Add Potassium Before Flowering Until End of the Season

Unless you want to produce all sorts of leaves rather than fruits, potassium needs to be given just before flowering until the end of the growing season. Potassium is an essential nutrient that promotes strong growth.

During this time, your potassium levels should be double that of the nitrogen in the fertilizer. Find a fertilizer with an 8-32-16 NPK ratio and use it as the instructions recommend.

Here are a few options:

Another option is to make a potassium-rich compost fertilizer tea. Bananas are excellent sources of potassium, and they release slowly, aiding in the growth of your plants. Making banana fertilizer tea is so easy.

  1. Gather the banana peels your kids leave after eating them.
  2. Cut the banana peels into pieces and put them into a jar.
  3. Cover them with water and let them sit in the jar OR bury the peels in the soil.

Phosphorus is essential during the time frame from flowering to ripe fruit as well. Most of the time, the soil in your garden has sufficient levels, but if you notice the fruits aren’t developing as you hope, consider adding more.

Watch for Fruit Growth & Add More Fertilizer as Needed

After you apply potassium during flowering, it’s time to wait and see what your plants do. Once the fruits develop into a golf ball size, it’s time to add more fertilizer to encourage more fruit production.

At this stage, phosphorus and potassium are the two most important nutrients. Adding compost tea is a great idea, and banana tea is great when you fertilize tomato plants.

If you notice your plants aren’t growing as they should, add more fertilizer – the ones recommended above that are heavier with the potassium and phosphorus. Continue to fertilize lightly every two to three weeks until the end of the growing season, especially with indeterminate tomato plants. Determinate tomato plants set their fruit growth at one time, so you need to apply less fertilizer.

How Do I Know if My Plants Need Nitrogen?

Nitrogen is a must-have nutrient for tomato plants, and it depletes easily in your soil. Since plants require nitrogen, in varying amounts, at all stages of growth, it’s essential to ensure your soil has plenty of nitrogen.

But, how do you know if they aren’t receiving enough?

Typically, if you enriched your plants with compost, they will receive ample amounts of nitrogen, but there is still a chance that the soil will require more. Nitrogen deficiencies often cause the bottom leaves of the tomato plant to turn yellow.

Leaves are a great indicator of the health of your plants.

Over-Fertilizing Tomato Plants

Everyone knows that a lack of nutrients will cause growing problems for plants, but excess fertilization is just as bad. While a lack of nutrients will cause your plant to struggle and produce fewer tomatoes, excess fertilizer may cause the plant to die on the spot.

Don’t worry; fixing it is typically easy even if you give too much to your plants.

But, how do you know if you gave your tomato plants too much fertilizer?

Here are a few signs of tomato over-fertilization.

  • Yellowing Leaves: Often times, excess nitrogen leads to yellowing tomato leaves because the plants are able to absorb enough water. That leads to the older leaves yellowing early.
  • Bushy Leaves & Delayed Flowering: When you give your plants too much nitrogen, it causes your plants to put on a lot of leaves and slows the flowering process. In some cases, flowers won’t form at all. However, delayed flowering may be difficult to pinpoint unless you are experienced with growing tomatoes.
  • Sediment on the Top of the Soil: Another sign of too much fertilizer is a heavy build-up of sediment and fungi growing over the soil surface.
  • Wilting Leaves
  • Sudden Loss of Leaves

Related: Did You Find Tomato Leaves Turning Yellow? Here are 10 Reasons!

Fixing over-fertilization is possible, but at times, it may be too late to solve the problem. Here are some suggestions.

  • Spread mulch, especially sawdust, over the soil because the decomposition process uses nitrogen. So, spreading an organic mulch over the soil or mixing it into the top layer of the soil will use up extra nitrogen in the soil.
  • If you see a build up of white salts on the top of the soil, remove this layer and dispose of it.
  • If your plants grow in containers, soak the soil throughly, allowing the water to drain out the bottom. In-ground plants should be soaked throughly. Repeat this process several times; it’s called flushing the soil.

Fertilizing tomato plants correctly is a sure-fire way to ensure your plants produce the largest harvest possible. Remember to change your fertilizer based where your plants are in their growing season since its nutrient needs change as the plants grow.

Happy gardening!

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