When to Use 3-1-2 Fertilizer | How and When to Use It

Even the best soil needs a little help sometimes and picking the right fertilizer can make all the difference to your landscape. 

It’s not always easy to decipher the labels or know how to choose the right blend of feed either. 

Using a 3-1-2 fertilizer is a common option in many domestic settings and is used by gardeners and plant enthusiasts the world over. The key is knowing when to use it and how to apply it and this article will uncover exactly that. 

Understanding 3-1-2 Fertilizer Label?

There are hundreds of fertilizer products on the market these days and understanding the best one to meet your needs and the needs of your plants can feel like a long-winded process. At the end of the day, you’re just looking for a product that will enhance the nutrient count in your soil so that you have a landscape that thrives. 

Long story short, once you understand the labels it can be easy to match a fertilizer product to meet your needs. 

Fertilizer labels include three numbers. These three numbers represent how much nitrogen, phosphorus, and potassium (NPK) – also known as macronutrients – the product contains. The label will also provide a list of all secondary ingredients – micronutrients – and fillers (if any). These include trace elements such as calcium, iron, copper, and magnesium that support plant health.

Let’s delve a little deeper now into what exactly an NPK ratio is and what it means for your soil and plant health. 

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N-P-K Ratio

The three digits that appear on fertilizing packages are the N-P-K ratio, or the amount of nitrogen (N), phosphorus (P), and potassium (K) found in the fertilizer. While fertilizers can include other ingredients, these three macronutrients are the most important.


Nitrogen is in everything from the plant’s leaves to its roots. Nitrogen supports the plant’s ability to produce chlorophyll and helps the plant make food to grow and develop. 


Phosphorus is another key element that helps plants grow new cells and tissue and to break down proteins for energy. Sufficient phosphorus levels support growth and development, through the root system. In flowering plants phosphorous also supports the development of buds and flowers.


Potassium also plays a role in growth and development, but it’s slightly different. Plants rely on potassium for the regulation of food, water, oxygen, and carbon dioxide. Potassium helps to make plants stronger and protects them against pests, diseases, and adverse external conditions such as frost.

3-1-2 Fertilizer Type

If you ever shopped for fertilizer, you’ll know that there are several application options available. Each has pros and cons depending on how your garden and what you are fertilizing.  These options fall into four main categories: 

  • Quick Release –Available in liquid or water-soluble formats that offer an instant boost of nutrients. 
  • Slow-Release – Powders, granules, or spikes that offer a steady stream of nutrients into the soil gradually. These rely on water and soil microbes to become active to start working.
  • Organic – made from natural materials such as animal bi-products (e.g. bones) and composted plant matter that is carefully selected because they naturally contain the macro or micronutrients that plants need.
  • Inorganic – Mass-produced using synthetic chemicals. Arguably more effective than gentler organic products but with the downside of potentially harming nature and nearby water sources.

Liquid Fertilizer Spray

Liquid fertilizers come in either a concentrated formula that requires dilution with water or as a pre-mixed and ready-to-use formula.

Gently shake or stir before use to ensure an even distribution of nutrients throughout the product. Liquid fertilizers can be applied with a sprayer that connects to your hose, with a spray bottle for smaller applications, or when mixed with water in a watering can. 

Due to the fast-acting nature of liquid feeds, you may need to reapply more frequently since run-off is likely.

Slow-Release Granules

Slow-release granules can offer a more cost-effective option, especially when purchased in bulk. Granules can be spread over the ground either by hand or with a spreader. Using a spreader makes the process of fertilizing large spaces quicker and easier. 

The gradual release of nutrients means that the fertilizer can take longer to start working but can also remain in the soil and continue to feed the roots of plants for longer. It also means that it doesn’t require as many applications.

Water Soluble Powder

As the name suggests, water-soluble options work by dissolving a concentrated powder in water to create a mixture. 

As with liquid feeds, these need to be applied via a sprayer and hose or watering can and distributed around the plant’s base. They too offer a quick-release of nutrients that need more applications when granules.

Fertilizer Spikes

Fertilizer spikes are mess-free and extremely easy to use. Just press or hammer them into the ground, and the spike breaks down and gradually releases nutrients into the soil. 

Spikes can work out to be the most expensive method of fertilizing because more is needed depending on the area of coverage. Plus there is a possibility that implanting spikes too close to the roots of plants, trees and shrubs can cause fertilizer burn.

What is 3-1-2 Fertilizer Used For?

You can use 3-1-2 fertilizer across a wide spectrum of non-flowering trees, shrubs, plants, as well as lawns. 

The relatively low ratio of macronutrients offers a gentle feed that is not only ideal for young plants, it can also minimize the risk of root or leaf burn in mature specimens that can result from over fertilizing. 

The 3% inclusion of nitrogen means that the health and color of stems and foliage will be enhanced especially during the active growing season. 

The low dose of phosphorous means that roots and bud development will get off to a good start, especially if used in spring at the start of the growing season. And the addition of potassium means that overall plant health and protection against pests and diseases are supported too.

Nutrient Deficiency

Plants are quite good at providing signals when they have a specific nutrient deficiency. For example, a nitrogen deficiency might present as yellowing leaves, limited growth, and little to no flowers or fruit. 

Phosphorus deficiencies can also reduce growth and typically present in older growth first. 

The yellowing and wilting of the leaves can indicate Potassium deficiencies in many plants.

In any event, the easiest way to find out what your plants need and to identify any deficiencies is to do a soil test. Soil test kits are cheap to buy, can provide peace of mind, and can save you time and expense in the long run. 

3-1-2 for Indoor Plants

A 3-1-2 fertilizer is a great option for houseplants, especially leafy varieties. The gentle formula is perfect for keeping over-fertilizing problems at bay. 

Do keep in mind that flowering varieties of house plants may require a fertilizer with more phosphorous if blooms are to be encouraged. 

3-1-2 for Trees and Shrubs

The soil of your home landscape differs drastically from a tree’s natural environment, so supplementing with 3-1-2 fertilizer keeps trees healthy. 

The nitrogen in 3-1-2 is best suited to evergreens and non-flowering trees and shrubs. This NPK ratio formula is suitable for use whenever fertilizing is required especially where the soil is already nutrient-rich and mulch is applied over winter.

For trees and shrubs that bloom, apply a fertilizer with higher phosphorus levels. Trees and shrubs that are susceptible to frost damage may also benefit from a fertilizer that contains a higher concentration of potassium. 

Vegetable Gardens

You can use 3-1-2 fertilizer in your vegetable garden if you know your soil is either lacking in nitrogen or if you are growing edibles such as leafy greens that benefit from a high-nitrogen fertilizer

In most cases, however, it is best to use a balanced feed such as a 10-10-10 fertilizer for use in a vegetable garden. Alternatively, when growing flowering edibles, use a high phosphorus fertilizer or one that you know is a specific fertilizer for pumpkins, squash or tomatoes, etc. 

Lawn and Grass

Using the right fertilizer on your lawn can help to prevent weeds from overtaking the grass. The ratios in 3-1-2 fertilizer are ideal because the nitrogen promotes growth that leaves no room for weeds to grow. Nitrogen is also what provides grass with that lush green and healthy appearance. 

Slow-release 3-1-2 fertilizer will ensure this low level of nitrogen keeps your grass healthy throughout the season. If used according to the manufacturer’s instructions, you’ll avoid a salt compound build-up that can otherwise lead to root or leaf scorching.

Flowering Plants

As flowering plants start to grow used 3-1-2 fertilizer to help them strengthen their root system. As the season goes on, they’ll need more a high phosphorus fertilizer to support bud development and create beautiful blooms.

How and When to Use 3-1-2

Follow the manufacturer’s instructions before using any fertilizer on your plants. The directions should be clearly printed on the label or available through the website. Stick with the recommended dosage to avoid fertilizer burn.

3-1-2 Application Rate

The 3-1-2 fertilizer is ideal for young plants, to give them a strong, healthy start as they take root. But since the ratios are so low, you can continue to use it to provide crucial nutrients for your plants, trees, and shrubs. 

Can You Use Too Much 3-1-2 Fertilizer?

Unfortunately, you can overdo it with any fertilizer. Too much nitrogen can increase salt levels in the soil and harm the plants. Greenery will turn yellow and look wilted, and the tips start to brown. You should notice this impact within a day or two of application.

3-1-2 Fertilizer FAQs