How to Fertilize Tomatoes

Tomatoes are heavy feeders that generally need quite a bit of fertilizer to get them through the season. The tricky part in learning how to fertilize tomatoes successfully is figuring out which fertilizer is best, how much to use, and when to apply it. Don’t worry though; fertilizing tomatoes isn’t as involved as it may seem.

Your tomatoes may not need fertilizer at all if you dig a generous amount of well-rotted manure into the top 8 to 12 inches (20-30 cm.) of soil at planting time. Manure is nutrient-rich but tends to be low in phosphorus, so balance things out by adding a little bone meal along with the manure.


If your soil is poor or if you don’t want to bother with manure, you can use a good quality fertilizer. Pay attention to the three numbers on the package, which indicate the levels of nitrogen (N), phosphorus (P), and potassium (K).

You can also keep things simple with a fertilizer especially formulated for tomatoes. We recommend either a good organic-based fertilizer (water soluble or liquid), or a certified organic fertilizer. The difference is that “organic-based” means the product is natural (not synthetic) and contains 20-25% organic based ingredients. “Certified Organic” means the products are from 100% plant or animal derived sources and have undergone 3rd party verification to ensure the integrity of ingredients meet and exceed organic standards.

For a good “organic-based” fertilizer we recommend the PRO-MIX Organic Based Liquid Fertilizer for Tomatoes, Vegetables & Fruits with a ratio of 3(N)-6(P)-12(K), or the water soluble PRO-MIX Organic-based Tomatoes, Vegetables & Fruits Fertilizer 9-16-16.

For a good “certified organic” fertilizer we recommend the PRO-MIX Organic Fertilizer for Tomatoes, Vegetables and Fruits with a ration of 4-4-8.


Unless you amend the soil with manure at planting time, you’ll want to boost the plants with a little fertilizer to get them off to a good start. Dig the hole, than place the fertilizer, in the amount recommended by the manufacturer, in the bottom. Cover the fertilizer with clean dirt to keep the fertilizer from direct contact with the roots.

Thereafter, side-dress your tomatoes with fertilizer every three to four weeks throughout the season.


To side-dress tomatoes, use the tip of your hoe to make a shallow furrow around the plant, at least 5 to 6 inches (12-15 cm.) from the stem. Sprinkle the fertilizer in the furrow at a rate of 1 to 1 ½ tablespoons (15-21 ml.) for each plant. Cover the fertilizer with soil and mulch.

Be extremely careful not to get fertilizer on the leaves or stem. Water well immediately after feeding to carry the fertilizer evenly down to the roots.


A water-soluble fertilizer is often easier to apply, especially for tomatoes grown in containers. Just mix the fertilizer in the watering can at a rate of about 1 tablespoon (15 ml) per gallon (4 L). Apply every one to two weeks throughout the season. If you’re using it in the garden, mix about 2 tablespoons (30 ml) per gallon (4 L).

You should avoid applying it during very hot or very dry conditions. Note that 4 L will cover approximately 4 square feet of your garden or the surface of ten 8’’ pots.

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