The Best Tomato Plant Fertilizer

Updated February 21, 2017

Growing tomatoes is an easy, low-cost way to enjoy a home-grown harvest. The most popular plants in the summer garden, these warm-weather vegetables require full sun, frequent watering and nutrient-rich soil to thrive. Tomato plants also are heavy feeders, needing steady doses of fertiliser during the growing season.

At Planting Time

When you prepare the soil for your tomatoes, the best fertiliser to incorporate is a slow-release, complete formula such as an 8-32-16 or 6-24-24. Once the young plants are in the soil, water them with a starter solution. These solutions are widely available at garden centres and nurseries, or you can make your own by mixing 0.454kg. of 8-8-8 fertiliser into 10 gallons of water, or 3 tbsp per gallon. Use 1 cup of the solution for each tomato plant.


After the plants have set their fruit, and every week or two thereafter, sidedress with 2 tbsp per plant of an 8-8-8 or 10-10-10 fertiliser. Tomatoes grown in clay soil will need to be fertilised less often than those grown in sandy soil. The Texas A&M University Extension warns that if you are using a fertiliser high in nitrogen, such as ammonium nitrate or sulphate, reduce the rate to 1 tbsp per plant.


If your tomatoes suffer from blossom-end rot, a soft decaying spot on the bottom of the fruits, add a calcium source such as agricultural gypsum or limestone when the flowers first open. If a soil test shows a deficiency in magnesium, sprinkle a handful of Epsom salts around each plant, then water thoroughly. When choosing a fertiliser for your tomato, look for a formula low in nitrogen, high in phosphorous and medium to high in potassium, according to the University of Missouri extension. If your formula is high in nitrogen, it will cause the plants to produce more foliage and branches than fruit.

How to Apply

When sidedressing tomatoes, keep the fertiliser at least 4 inches from the plants' stems. Work it well into the soil to avoid fertiliser burn. Liquid fertilisers can be applied through a drip system, while foliar applications are sprayed or poured directly onto plants' leaves. Liquid and foliar formulas will need to be applied more frequently than slow-release formulas.

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About the Author

Aileen Clarkson has been an award-winning editor and reporter for more than 20 years, earning three awards from the Society of Professional Journalists. She has worked for several newspapers, including "The Washington Post" and "The Charlotte Observer." Clarkson earned a Bachelor of Arts in journalism from the University of Florida.