If you like to grow your own fruits and vegetables, tomatoes are a delicious and versatile choice that can thrive in both huge gardens or on small balconies. While tomatoes are relatively easy to grow, they still require nutrition to produce well. To get those necessary nutrients, tomato plants require ongoing fertilization during their growing season. Ahead, learn when and how to administer tomato fertilizer and gain insights on which type will produce the best harvest.
- Emma Biggs, expert gardener and author of Gardening with Emma
- Michelle Hawks, lead horticulturist at Reynolda Gardens
- Rebecca Sears, gardening expert and CMO for Ferry-Morse, an online plant and seed retailer
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What Nutrients Tomatoes Need
Tomato plants need three main nutrients from fertilizer—nitrogen, phosphorus, and potassium—along with other trace minerals to grow and fruit successfully, says expert gardener Emma Biggs.
Most fertilizers are a combination of those three components; the packaging will indicate the percentage of each. For example, if there's an equal ratio of nitrogen, phosphorus, and potassium, the fertilizer may be labeled as 10-10-10; if more nitrogen is present, it may appear as 15-10-10.
To know how much of each nutrient your plant needs, Michelle Hawks, the lead horticulturist at Reynolda Gardens, recommends having your soil tested. This will gauge the levels of each element in your soil, as well as its pH, which Hawks says should be around six to seven for a tomato plant. Knowing which nutrients your soil needs more or less of will inform you on the specific number series to look for when purchasing plant food.
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Types of Tomato Fertilizer
According to Biggs, the variety of fertilizer you use is a personal choice. She tells us she's tried many types of tomato fertilizers over the years and has discovered that no single product is best for everyone.
To help guide your choice, consider which application method is easiest for you, and think about if you want to use an organic or non-organic product. Hawks actually uses both types, noting that organic fertilizers improve the soil year-round while inorganic fertilizers help boost production volume.
- Foliar Spray: Foliar spray is a type of fertilizer that's diluted in water and sprayed directly onto your plant's leaves. Biggs says it's best to apply this type in the morning.
- Liquid Fertilizer: This variety should be mixed with water following the instructions on the packaging and poured at the base of the tomato plant. "Try not to get the lower leaves wet or let the water splash up onto the lower leaves to help prevent diseases from spreading," Biggs says.
- Granular Fertilizer: If you're using granular or pelletized fertilizer, be sure to sprinkle it around the base of the plant as directed.
- Organic: "Organic fertilizers are made from natural sources such as compost, organic waste, bone meal, or fish emulsion," says Rebecca Sears, gardening expert and CMO for Ferry-Morse. "Organic fertilizers are slower-acting, but over-fertilizing is less likely." These organic soil amendments are typically mixed into the soil before planting your tomatoes.
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How to Make Your Own Tomato Fertilizer
There are plenty of different recipes you can follow when making your own tomato fertilizer, but Hawks' preferred option is a combination of equal parts mixed wood ashes, chicken or horse manure, and compost, like shredded leaves and grass clippings.
- Combine equal parts wood ash, manure, and compost in a 5-gallon bucket.
- Mix well.
- Apply the organic tomato fertilizer to the base of the plant.
- Water thoroughly.
You can also include bone meal—a mixture of finely and coarsely ground animal bones—in your homemade fertilizer. The phosphorus-rich ingredient will give your fertilizer a nutrient boost. Another additive is Epsom salt, which is high in magnesium.
When to Fertilize Your Tomato Plants
How often you fertilize your tomatoes depends on whether you're growing them in the ground or in containers.
- In-Ground: Sears suggests fertilizing in-ground tomatoes once every four to six weeks throughout the growing season.
- Containers: Container gardens require more frequent fertilizing since they don't have the same access to nutrients. Aim for once every two to three weeks.
"If you miss a week, it's not the end of the word, but staying on top of fertilizing will help to keep your plants healthy and thriving," Biggs says.
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How to Fertilize Your Tomatoes
The method by which you feed your tomatoes depends on the type of fertilizer you're working with. Foliage spray, for example, needs to be applied directly to the leaves, while granular fertilizer should be sprinkled over the soil. Make sure you follow the manufacturer's label for step-by-step instructions—not doing so is why many people make the mistake of fertilizing their plants too much or too little, according to Hawks.
Common Mistakes to Avoid
Fertilizing your tomatoes is crucial to production volume and quality, but as with anything, there is room for error. Make sure to avoid these common tomato fertilizer mistakes.
- Over-Fertilizing Your Tomatoes: There's a fine line with how much fertilizer to give tomatoes, and this is true of both organic and synthetic options. "High mineral levels can cause instant damage like root burn, and long-term chemical use can alter the pH balance of your soil, which can cause a harmful build-up of mineral salts," Sears says.
- Applying Fertilizing Too Close to the Stem: When your plant comes into direct contact with certain types of fertilizer, it can burn the delicate stems and roots. Apply fertilizer a few inches away from the base of the plant and water thoroughly afterward.
- Not Accounting for pH Levels: Tomatoes prefer slightly acidic soil with a pH between 6.0 and 7. If your soil is too acidic or too alkaline, the plant won't be able to take up the nutrients in the fertilizer effectively.
- Treating Container and Ground Plants the Same: "If you’re growing your tomatoes in containers, make sure to adjust fertilization as your plants will have different nutrient requirements than those grown in the ground," Sears says." You may have to fertilize your container-grown tomatoes more frequently to replenish nutrients lost through watering."
Always follow the usage instructions on the product label to ensure your tomato plants get the right amount of fertilizer and to ensure proper application.
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