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

As a homeowner, you pride yourself on ensuring your lawn and landscaping look their best. But factors beyond your control, including extended drought and poor growing conditions, can wreak havoc. You may be wondering whether you’re using the right fertilizer or if you should use it at all. 

This article will discuss the purpose of 13-13-13 fertilizer and when and how to use it. The information below will also examine 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 nutrient elements are in equal measure 13-13-13. These numbers represent the percentage of nitrogen, phosphorus, and potassium. These are the three primary or macronutrients that plants and turf need to grow. 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.

Why Use a Balanced Fertilizer?

You already know that nitrogen stimulates the growth and color of visible grass blades. But it’s phosphorus that helps feed and grow roots. And potassium is responsible for ensuring your landscaping gets the right balance of nutrients and water it needs. 

Balanced fertilizer ensures an equal amount of the chemicals and 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 13-13-13 Fertilizer Label?

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. 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 hazards if it’s allowed to get into wastewater, some jurisdictions restrict how much fertilizer can contain. This is why you 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. Plants and grasses need phosphorus to develop and maintain strong root systems. 

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 landscaping’s general growth and maintains growth during the season. However, your trees and lawns also rely on potassium to keep healthy during dormant periods. Having enough potassium stores is critical for developing drought, cold, and disease tolerance. 

Impact of Soil pH

Your soil’s existing pH will impact how nitrogen, phosphorus, and potassium change it. 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 phosphorus 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 Type

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 will need to be applied using a watering can, sprayer, or a hose, and depending on what method to use, the amount applied will vary. 

Water Soluble Powder

Powder fertilizer options can either be sprinkled directly into the soil around the base of plants, trees, and shrubs or diluted with the correct ratio of 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

This is the type of fertilizer you’re probably the most familiar with if you have put nutrients on your lawns before. 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 eventually 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

Just like any other balanced fertilizer, the feeding schedule has an important part 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 half an inch of a tree’s perimeter. 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. The same applies to shrubs.

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 a single 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

Got questions? Here are some answers!