What is 13-13-13 Fertilizer? | When to Use Triple 13

As a homeowner, I’m sure you pride yourself on your lawn and landscaping always looking their best. But factors beyond your control, such as extended drought or poor growing conditions, can wreak havoc on an otherwise good property. You may be wondering whether you’re using the right fertilizer or if you should use it at all. 

In this article, I’ll discuss the purpose of 13-13-13 fertilizer and explain when and how you should use it. You’ll also find information about the different forms of fertilizer, and which is best to use on lawns, shrubs, trees, flowers, and gardens. Let’s get started!

What Is Triple 13 Fertilizer Used For?

Triple 13 fertilizer is a balanced fertilizer, meaning all three macronutrients are present in equal quantities, with an N-P-K ratio of 13-13-13. These numbers represent the percentage of nitrogen, phosphorus, and potassium. Each of these nutrients has specific effects or purposes. 

For example, nitrogen stimulates growth and is responsible for the lush greenness of your lawn and plant foliage. However, too much nitrogen can burn the grass and even kill its roots. You may have noticed this if you have a dog or have let nitrogen-rich fertilizer sit on your lawn during hot summer days. 

Triple 13 fertilizer is usually used to jump-start the growth of grass, gardens, flowers, and shrubs during the early spring months. Balanced fertilizer also helps establish new lawns and other forms of landscaping.

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Why Use A Balanced Fertilizer?

You already know that nitrogen stimulates the growth and color of grass blades. But it’s phosphorus that helps feed and grow roots. Meanwhile, potassium is responsible for ensuring your landscaping takes in the right balance of minerals and water.

Balanced fertilizer provides an equal amount of the key nutrients grass and plants need to sustain growth. For gardens, it’s an effective way to promote early growth and give the plants a boost halfway through the growing season.

As previously stated, balanced fertilizer is best for newly established plants, bushes, trees, and lawns. Both the roots and the visible parts of plants need help to get established, especially in clay or rocky soils. 

Understanding Fertilizer Labels

On all fertilizer bags or packaging, there is a set of three numbers which represent the percentage of nitrogen, phosphorus, and potassium in that order. So for example, a number sequence that reads 20-5-0, indicates 20% nitrogen, 5% phosphorous, and 0% potassium. 

N-P-K Ratio

Soils naturally contain nutrients that trees and lawns need to sustain growth. However, soils can lose nutrients or become unbalanced over time. By carrying out a simple soil test, you’ll get to know the pH of your soil and what type of N-P-K ratio you need. 

In addition, the growing season, climate, and existing plant health will all influence the ideal N-P-K ratio.


According to Rutgers University, a lawn needs one pound of nitrogen for every 1,000 square feet if the fertilizer contains 20% nitrogen. With fertilizer that contains 13% nitrogen, you need 7.7 pounds of fertilizer for a 1,000 square foot lawn. High nitrogen fertilizers promote visible growth and healthy color.


Since phosphorus can cause environmental damage if it’s allowed to get into water sources, some jurisdictions restrict how much fertilizer can contain. This is why you might see some types of fertilizers show up as not available in your area if you try to order products online.

However, some soils can either be naturally deficient or become low in phosphorus. Overwatering or dry conditions can also cause the depletion of nutrients.

If it’s later in the growing season or you’ve already got established sod and trees, you probably don’t need that much phosphorus in your fertilizer. But if you’ve just planted a new tree, extended your garden, or put in new sod, you need a good dose of phosphorus. 


This nutrient boosts your landscape’s general health and maintains growth during the season. Your trees and lawn also rely on potassium to keep healthy during dormant periods. Adequate potassium stores are critical for good drought, cold, and disease tolerance. 

Impact of Soil pH

Your soil’s existing pH will impact how nitrogen, phosphorus, and potassium interact with plant roots. At the same time, nitrogen can increase the acidity of your soil’s pH. Ammonium-based nitrogen stands a higher chance of acidifying your soil, whereas nitrate-based fertilizers do not. 

Phosphorus has less of an impact on pH balance than nitrogen but can still raise its acidity. 

Potassium usually does not have much influence on soil pH. If your soil’s pH is too alkaline, you may need a fertilizer with a higher concentration of nitrogen and phosphorus.

Soil that is already too acidic may need amendments other than nitrogen and phosphorus.

Fertilizer Types

Fertilizers, whether organic or synthetic, come in different forms. Each of these forms has advantages and drawbacks. Below are the main forms you’ll find.

Liquid Concentrate

Liquid concentrate fertilizer needs to be diluted with water according to the instructions on the label. 

It can be applied using a watering can, sprayer, or a hose, and depending on what method is used, the amount applied will vary. 

Water-Soluble Powder

Powder fertilizers can either be sprinkled directly into the soil around the base of plants, trees, and shrubs or diluted with water. Water-soluble fertilizers are a cost-effective method of feeding. However, due to their fast-acting nature, they do carry a risk of root burn and leaching.

Slow-Release Granules

Slow-release granules need to be applied using a spreader, according to the instructions on the packaging.

Some types of slow-release granules need to sit on the lawn for up to 48 hours before you water the fertilizer in. Other types, usually those that don’t include weed killer, need to be watered in after application.

Slow-release granules distribute nutrients to your grass and plants over time instead of all at once. This is beneficial if you want to avoid burned grass, during warmer periods of the growing season, or if you want to sustain growth over a few months. 

Fertilizer Spikes

Fertilizer spikes are hammered into the ground around the dripline of a tree, bush, or shrub. You can also place them in a garden bed, within a potted plant, or on your lawn. 

These spikes break down over time and distribute nutrients into the soil. Your plant’s roots are exposed to the nutrients and the roots absorb them. 

Spikes are an easy-to-use, mess-free solution to fertilizing and are safe to use around pets and people provided they are buried well in the soil. 

The downside is they are typically more expensive than other fertilizer types and you have to use more than one of them for taller, more established trees and shrubs. 

How and When To Use 13-13-13 Fertilizer

With any fertilizer, the feeding schedule has an important role to play in successful plant growth. Whether it be a 6-6-6 fertilizer or a 20-20-20 fertilizer, the timing and frequency of nutrients are critical to success. Here’s a more detailed breakdown of how to use balanced fertilizers for different types of plants.

Trees and Shrubs

With trees and shrubs, it’s best to put down half a pound of balanced fertilizer per 1/2 inch of trunk diameter. It’s a good idea to apply this at the beginning of the growing season. Put down another application in the late summer or early fall.

Fruit Trees

Fruit trees can also get the same amount of balanced fertilizer twice during the growing season.


A balanced fertilizer should be applied to flowers every 12 weeks. It’s best to use 1 pound for every 100 feet of flowers. This amount is for each application.

Vegetable Gardens

You’ll want to apply a balanced vegetable garden fertilizer to the soil before planting any seeds or plantings. This should take place in the early springtime. 

Then go ahead and sprinkle more on as a topper around mid-season to give your plants a boost.

Bear in mind that different types of vegetables need different types and amounts of fertilizer, depending on the stage of growth. Tomatoes, for example, need high nitrogen, to begin with, and phosphorus once flowers and fruit are shown to help increase yield and growth.


Providing you use nutrient-rich soil for your houseplants, they will benefit from a balanced fertilizer such as triple 13. 10-10-10 fertilizer or a diluted 16-16-16 fertilizer are also good options for houseplants. 

Always fertilize houseplants with caution and ideally use a liquid or diluted feed that can be allowed to run off. Intersperse feeding with watering so that any build-up of fertilizer residue has a chance to get flushed out.

13-13-13 Fertilizer FAQs