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Nitrogen for Tomato Plants

tomatoes image by Freeze Frame Photography from

The many varieties of tomatoes are good additions to summer vegetable gardens, and are fairly carefree. They just need weekly watering and a couple of fertilizer applications during their growing season. Nitrogen is an important nutrient that tomatoes need early in their growth cycle, but after they start setting fruit, it’s important to cut back on the nitrogen because it will cause plant growth at the expense of fruit production.


Tomatoes are a relatively new addition to the dinner table. Erroneously thinking the tomato was poisonous, people avoided eating this member of the nightshade family for many years. Coming from its native South America, the tomato became a popular food in Italy around 1550. It soon spread to England, Spain and other parts of Europe, becoming a culinary staple by the 1850s. In America, Thomas Jefferson was one of the first gardeners to grow tomatoes around 1781. Not until the 1830s did the tomato gain a strong foothold in the northeastern states.

Varieties of Tomatoes

Tomatoes come in a wide range of shapes and sizes. From the small cherry tomato varieties to the enormous Beefsteaks, there is a tomato for every need and every climate zone. Many hybrids have been developed—for example, the Oregon Spring tomato thrives in the cooler summer temperatures of the Pacific Northwest, and the Solar Set tomato is adapted to the very high temperatures of southern Texas, Arizona and Florida.

Take It Easy on the Nitrogen

Although tomatoes need nitrogen during their early lives, you need to be careful not to give them too much of this nutrient. Doing so can result in dark green plants with thick stems and leaves that curl instead of growing flat. Fruit set will be poor on plants that receive an excess of nitrogen in their first two to three months of life. If you use a special plant food designed for tomatoes, it will result in strong, healthy plants that will give you the maximum amount of fruit.

Signs of a Nitrogen Deficiency

Leaves that start to turn yellow on the lower part of a tomato plant can indicate that the plant is suffering from a lack of nitrogen. To correct this problem, spray your plant with a dilution of fish emulsion or apply a granular plant food to the soil surrounding your plant. A fertilizer with an N-P-K ratio of 20-10-10 will provide your plant with a good boost of nitrogen.

Good Soil Gives Good Nitrogen

Tomato plants respond well to compost and manure that you dig into their planting area. They also thrive when you mulch them with any type of compost because this will give them continuous nutrition. If you plant a cover crop of alfalfa or clover after your summer tomato harvest is complete, these plants will add nitrogen to the soil when you chop them down and dig them under in late winter.

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