The Ultimate Tomato Fertilizer Guide: How to Feed Tomatoes for a Bigger Harvest

Tomatoes, like many annuals, are heavy feeders and do better when provided with plenty of nutrients to grow through the season. Fertilizers, either chemical or organic, can help provide the extra nutrients that tomatoes need to grow quickly.

Understanding which fertilizer to use (and when to add it) will give you the best chance of nurturing robust plants and quality fruits. What is a good tomato fertilizer? When should you be fertilizing tomato plants?

Keep reading for the answers to all your questions about fertilizing tomatoes, plus our plant experts' recommendations for the best tomato fertilizers for huge harvests.

Do Tomatoes Need Fertilizer?

Tomatoes need nitrogen, phosphorus, and potassium (often abbreviated as NPK) to fuel leaf, root, and fruit development. Fertilizers list three numbers on the label that indicate the ratio of each of these three macronutrients in that particular formula.

Tomatoes are big feeders, which means they need lots of all three major nutrients. Before choosing a fertilizer, it's essential to test your soil first. This will tell you exactly what your soil is lacking and what you need to supply for your tomatoes so they thrive all summer.

You can get a cheap and easy-to-use soil test kit from Amazon or from many garden centers. Having a soil pH of 5.5 to 7 is also ideal for growing tomatoes. It's a good idea to perform a pH test prior to the season’s planting as well as a nutrient test.

Best Fertilizer for Tomatoes

If your soil is correctly balanced or high in nitrogen, which is the first number on a fertilizer label, use a feed that is slightly lower in nitrogen and higher in phosphorus, such as a 5-10-5, 10-20-10, or 5-10-10 fertilizer.

If you are slightly lacking in nitrogen, use a balanced fertilizer like 8-8-8 or 10-10-10. High amounts of nitrogen can lead to excess production of leaves at the cost of fruit production, so generally the best fertilizer for tomatoes is one that is lower in nitrogen or balanced.

When transplanting tomatoes, a starter food high in phosphorus will spur cell formation, root growth, and shoot formation. Phosphorus amounts are indicated by the second number in the ratio. Potassium, which is the third number, helps plants uptake water and nutrients.

The best tomato fertilizer will also include calcium, magnesium, and other trace elements. A specific vegetable fertilizer that's designed to give tomatoes all the macro and micronutrients they need to produce both healthy foliage and tons of fruit is your best bet. Content Editor Laura Walters has had great success with this organic granular fertilizer from Jobe's.

Types of Tomato Fertilizers

Organic fertilizer is a very popular way to feed tomato plants. You can use synthetic fertilizers, but they only provide a quick fix. A much better option is to use a slow-release fertilizer or to amend the soil with organic materials that will feed tomato plants all season long.

Well-rotted manure and compost are perfect for this purpose. Work them into the soil to a depth of at least 6 inches (15 cm) several weeks prior to planting. This will give the amendment time to begin releasing gentle nutrients.

There are water soluble foods, granular, foliar, and time-release formulas available as well. A time-release fertilizer is ideal for forgetful gardeners who don’t want to stick to a strict feeding schedule.

Homemade Tomato Fertilizers

There are many common organic items that can enhance growth and fruit production in tomatoes. Here are a few DIY fertilizer ideas that use items you probably already have at home that can give tomatoes a boost:

• Wood ashes are an excellent source of potassium.
• Using epsom salt on tomatoes will provide magnesium to stave off yellowing leaves.
• Chopped up banana peels provide a boost of potassium, as does kelp meal, which is a great organic fertilizer that's available online from Amazon or at many local nurseries.
• Coffee grounds contain 20% nitrogen and are a slow-release, gentle delivery of this necessary macronutrient that fuels leaf development.
• Using eggshells on tomato plants can help prevent blossom end rot by providing a small boost of calcium. Blend or crush them into a powder first to help plants absorb the calcium faster.

These homemade tomato fertilizers can help plants get some of the nutrients they need, but a better way to enhance the nutrition in these items is to use them to make compost at home.

Starting a compost pile or investing in a simple compost tumbler, like this one from Amazon, will help you produce tons of black gold that will boost your tomato crops for years to come.

When to Fertilize Tomatoes

In addition to adding a soil amendment prior to planting, it's a good idea to incorporate a starter food at the same time. Work the fertilizer well into the soil and select one that is high in phosphorus such as 5-10-5, like this natural root stimulator from Amazon.

Once the first fruits emerge, feed your plant again. Foliar applications of magnesium will help reduce yellowing leaves on tomatoes when the plant is in magnesium poor soil.

Several weeks after planting, a sidedressing of calcium nitrate will help form strong cell walls in your fruit and prevent blossom end rot in tomatoes. Apply this 6 inches ( 5 cm) away from the stems to prevent root burn.

A safer, organic alternative that provides calcium as well as the other nutrients your tomatoes need is this Tomato-tone fertilizer from Espoma. It works on other vegetables in your garden, too.

Apply slow-release organic fertilizers like this at planting, throughout the season, and when you harvest your first tomatoes. Follow the label for specific directions for each individual fertilizer formula.

If you grow tomatoes in containers, you need to fertilize plants more frequently. Nutrients leach out of the soil through the drainage holes every time you water, so you need to replenish them more often with a dose of plant food.

The best time to fertilize is in the evening as the sun goes down or after a rain. Container plants will benefit from a time-release formula.

How to Fertilize Tomatoes

When fertilizing tomatoes at planting, mix the fertilizer in with the soil at the bottom of the planting hole, then place some unfertilized soil on top of this before placing the tomato plant into the hole. If raw fertilizer comes in contact with the roots of the tomato plant, it can cause fertilizer burn.

When fertilizing tomato plants after the fruits have set, make sure to water first. If your tomato plant isn’t watered well before being fertilized, it can take up too much fertilizer and get burned.

After watering tomatoes, spread the fertilizer on the ground starting approximately 6 inches (15 cm) from the base of the plant. Fertilizing too close to the tomato plant can result in fertilizer running off onto the stem and burning the tomato plant. If you broadcast fertilizer all over your garden beds, make sure to rinse it off the plant leaves to prevent burning.

Shop Fertilizing Essentials

Looking for additional tips on growing perfect tomatoes? Download our FREE Tomato Growing Guide and learn how to grow delicious tomatoes.