What is 13-13-13 Fertilizer Good For? – When and How to Use It? 

Picking a fertilizer can be complicated.  You have to consider what plants you are fertilizing, what growth stage the plants are in, and what kind of soil you have.  While trying to pick one fertilizer from the hundreds in the store, you may wonder, “What is 13-13-13 fertilizer?” 

Need a hand figuring out what fertilizer to use?  This guide will tell you all about 13-13-13 fertilizer and when to use it. 

What Is 13-13-13 Fertilizer? 

Triple 13 fertilizer is composed of thirteen percent nitrogen, thirteen percent phosphorous, and thirteen percent potassium. The numbers on the front of the fertilizer bag are explained in more detail in this article

Briefly, nitrogen is in every cell of the plant and all the compounds it makes. Without nitrogen, the plant can’t grow. Phosphorous helps with strong roots, healthy growth, and to trigger blooms. Potassium also helps produce healthy plants that can resist diseases.

Triple 13 is considered a balanced fertilizer because all the numbers are the same. This fertilizer is best for new and established ornamental plants, such as flowers. 

What Is 13-13-13 Fertilizer Used For? 

What Is 13-13-13 Fertilizer Used For?
Marigold Photo by Stephanie Suesan Smith

Triple 13 fertilizer is usually used in the spring as the initial fertilizer of the year. The balanced formula is a good choice if you do not have a soil test. Triple 13 fertilizer can also be used to fertilize a new area before planting new ornamental plants. While you can use triple 13 fertilizer on any plant, including vegetables like tomatoes, it is most often used on ornamental flowers. You may also use triple 13 during the growing season to add nutrients your plants need to the landscaping bed or row.

When Do I Apply 13-13-13 Fertilizer? 

Triple 13 fertilizer is best for the initial fertilizer of the year. The balance of nitrogen, phosphorous, and potassium gives most ornamental plants the nutrients they need to grow for six to eight weeks. Triple 13 can be reapplied to everything but lawns throughout the growing season. Turf grass should only be fertilized once in the spring and once in the fall with triple 13. It needs nitrogen for the rest of the year.  

How Do I Apply 13-13-13 Fertilizer? 

The exact amount of triple 13 fertilizer you need depends on what plant you are fertilizing. The label instructions for each fertilizer will tell you how to apply that fertilizer. Here are some examples of what you can expect to use when fertilizing different types of plants.

Annual Flowers

For annual flowers, spread 2 1/2 cups per 100 square feet out after your bed is prepared for planting. Work the triple 13 fertilizer into the top two to three inches of soil. Plant your annual flowers as usual. Every six to eight weeks, spread another 1 1/4 cups per 100 square feet.

Existing Ornamental Plants

For existing ornamental plants, including shrubs, you typically spread 2 1/2 cups of granular triple 13 fertilizer per 100 square feet. Do not let the fertilizer touch the plants. Every six to eight weeks, spread 1/2 cup per 100 square feet. Stop fertilizing about one month before the first frost.

Bulbs and Tubers

For bulbs and tubers, spread three cups of triple 13 per 100 square feet before planting the bulbs. Work into the top two to three inches of soil. If you are planting your bulbs and tubers in a row, use 2 1/4 cups per 100 feet of row. Place triple 13 fertilizer in the trench the bulbs and tubers will go in, then cover with an inch of soil. Place the bulbs and tubers on the soil. The fertilizer should not touch the bulbs.

Vegetable Gardens

For vegetable gardens, use 2 1/2 cups per 100 square feet before turning the soil for the new season. Alternatively, you can wait until the soil is turned and spread 2 1/2 cups per 100 square feet and work the fertilizer into the top three inches of soil. If planting in rows, use 1 1/4 cups per 100 feet of row. Place the fertilizer two inches from the plant or seeds in a trench two inches deeper than the seed or plant. Cover the trench in soil. For vegetables that grow a long time, like onions or corn, spread 1 1/4 cups of fertilizer per 100 feet of row six inches from the plants and parallel to the row every six to eight weeks until harvest.


For trees, apply three pounds per 1000 square feet of canopy. Spread the fertilizer directly under the drip line.


For lawns, spread 1.9 pounds per 1000 square feet using a fertilizer spreader. The fertilizer can be applied again in the fall. Do not exceed two applications per year.

Always water your plants after applying fertilizer. Granular fertilizer requires water to activate it and send the nutrients into the soil.

Liquid 13-13-13 fertilizer is not usually used. Spring fertilizers need to be slow-release so they last well into the growing season, and liquids are not slow-release. Liquid triple 13 is not practical because of the large amount of liquid needed and the frequent applications required.

Where Do I Buy 13-13-13 Fertilizer? 

Triple 13 fertilizer can be bought at garden supply stores online, such as Amazon. This fertilizer is sometimes carried by big box stores such as Lowes and Home Depot.

My 13-13-13 Fertilizer Recommendations

Control Release Plant Food 13-13-13 contains all twelve of the nutrients plants need to grow and thrive. These nutrients are encased in a coating that slowly dissolves, releasing the fertilizer over three to four months, so you do not have to fertilize your plants as often. Control Release Plant Food 13-13-13 is best on bulbs, ornamental plants, and bedding plants.

For landscape beds, simply spread four pounds of Control Release Plant Food 13-13-13 per hundred square feet, then work into the top two to three inches of soil. Repeat every three to four months. Water the plants after you fertilize them. 

For container plants, use 1/8 teaspoon per inch of pot diameter or ½ teaspoon per gallon of pot. For sensitive houseplants, use half of the recommended amount. Water the plant after you fertilize it. 

What Are the Ingredients in Triple 13 Fertilizer? 

purple flowers in grass
Monkey Grass in Bloom Photo by Stephanie Suesan Smith

The exact ingredients in a triple 13 fertilizer depend on the brand. Each bag of triple 13 is guaranteed to have thirteen percent nitrogen, thirteen percent phosphorous, and thirteen percent potassium.

Some brands also include other nutrients that plants need. In addition, some manufacturers put soil microbes and nutrients for soil microbes in the fertilizer to help make the nutrients more available to the plants.

Finally, some manufacturers include proprietary ingredients to help plants use the nutrients in the fertilizer. The rest of the fertilizer is filler to make it easier to spread and compounds to retard spoilage. 

Some triple 13 fertilizers are organic, but they are difficult to find. Most triple 13 fertilizers are conventional.

Liquid formulations of triple 13 are also difficult to find. Granular formulations are generally slow-release, so they last a long time.

In lawns, the phosphorous and potassium may feed your ornamental plants all spring and summer long, and you will only have to supplement the triple 13 fertilizer with nitrogen midway through the growing season. You can also reapply the triple 13 in the fall on turf grass.

Frequently Asked Questions

How long does it take triple 13 to work?

Triple 13 usually takes a week to start working because it takes that long for the coating to dissolve enough to release the first nutrients.

How long does triple 13 fertilizer last? 

Most formulations last six to eight weeks before you need to apply more fertilizer. Do not reapply the fertilizer to lawns until fall, and only apply triple 13 twice per year to turf grass.

Is 13-13-13 good fertilizer for fall? 

Triple 13 may be applied to annuals until they are killed by the cold. This fertilizer should not be used on perennials, shrubs, or trees within a month of the average first frost date. Triple 13 can be applied to turf grass in the fall, but only once.

Will 13-13-13 fertilizer kill weeds? 

No, triple 13 fertilizer will not kill weeds. Some products include a weed killer and triple 13 fertilizer, which will kill weeds, but triple 13 alone will not kill the weeds.

Will 13-13-13 fertilizer burn grass? 

If you exceed the amount listed on the fertilizer label, you can burn your grass. In addition, if you apply triple 13 to your grass more than twice a year, you can burn your grass.

Will 13-13-13 fertilizer cure my sick plants?

If your plants are sick because they lack nitrogen, phosphorous, or potassium, triple 13 will help. If your plants have a disease or pests, triple 13 will not help them.

In conclusion, 13-13-13 fertilizer is a fertilizer that contains thirteen percent nitrogen, thirteen percent phosphorous, and thirteen percent potassium. The fertilizer may contain other nutrients or proprietary ingredients to help the plant use the nutrients in the fertilizer. Some triple 13 fertilizers are organic, while most are synthetic. Granular fertilizers are best for ornamental plants because they are slow-release and will last several months before you have to reapply them.

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Stephanie Suesan Smith

Stephanie Suesan Smith has a Ph.D. in psychology that she mainly uses to train her dog. She has been a freelance writer since 1991. She has been writing for the web since 2010. Dr. Smith has been a master gardener since 2001 and writes extensively on gardening. She has advanced training in vegetables and entomology but learned to garden from her father. You can see her vegetable blog at https://stephaniesuesansmith.com/.

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