Choosing the right fertilizer can be challenging for many plant lovers as there is a great variety of these products available on the market. Whether you’re feeding your vegetable garden or going for a greener, thicker lawn, applying the wrong fertilizer could do more harm than good.
There are various types of plant-specific and general-purpose fertilizers to choose from. These are also available in various forms, like granules, liquid, or water-soluble. Moreover, they are of several types depending on their application, such as foliar or directly applicable on the ground. Fertilizers are also divided into slow and fast release fertilizers, organic or synthetic, and so on.
I’m sure you understand by now why choosing the right fertilizer might be an intimidating task. Many get lost in these details and end up choosing the wrong fertilizer for their plants because they ignore one of the most important aspects of choosing a fertilizer – its N-P-K ratio.
Even though these numbers may seem extremely confusing at first, if you know what this ratio means, it will help you a lot to choose the right fertilizer for your plants.
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What Is N-P-K In Fertilizers?
As you’ve probably seen, all fertilizers display a set of three numbers on their packages. These represent the basic nutrients all plants need. Some need a balanced blend, while others need more of one nutrient than another. To choose the correct blend for your specific application, you need to know what the numbers represent, what each nutrient does, and which blend is best for the plants you’re feeding.
Plants require about 16 nutrients to live and these are divided into macronutrients and micronutrients. What plants need in larger amounts are the macronutrients.
While there are about 9 essential macronutrients, plants consume in larger quantities 3 of them:
In chemistry, the symbols that represent these three elements are N, P, and K, respectively.
The set of these three numbers printed usually near the product’s name on a bag of fertilizer represent the percentage of total weight that is nitrogen (N), phosphorous (P), and potassium (K). Thus, if a 10-pound package of fertilizer has N-P-K numbers of 12-4-2, it would contain 1.2 pounds of nitrogen, 0.4 pounds of phosphorous, and 0.2 pounds of potassium. The remaining 8.2 pounds is filler.
Common fillers include sand and granular limestone. This filler helps ensure that the fertilizer is spread evenly. Too many of these essential nutrients ending up in one spot can damage plants.
What Each Of The N-P-K Nutrients Does?
Knowing what each of the main ingredients in fertilizer do will help you choose the proper mix. If you look at a bag of lawn fertilizer, you’ll notice that the nitrogen content is very high compared to the amounts of phosphorous and potassium. That’s because nitrogen promotes the vigorous growth of leaves and enhances their color, thus giving you a thick, very green lawn.
If your grass doesn’t have a rich green color and isn’t growing very well, this is an indication that more nitrogen is needed. If, however, you use lawn fertilizer in your flower or vegetable garden, you could cause your plants to have very healthy leaves and no flowers or vegetables at all. The lawn mix contains too much nitrogen for this type of application.
Phosphorous promotes healthy root development as well as fruit, vegetable, flower, and seed production. Phosphorous also helps plants to better utilize other nutrients. Vegetable and flower gardens that aren’t producing as expected may be lacking phosphorous.
Potassium is the multivitamin of the plant world, promoting general health. Among its wide-ranging benefits, potassium helps plants grow healthy root systems, makes them more disease tolerant, and helps them survive cold temperatures and drought.
Choosing The Right N-P-K Ratio
Many fertilizers are mixed to promote the growth and health of specific plants, like lawn fertilizer that has a high nitrogen content for greener, thicker grass, or a mix intended for azaleas, that includes the extra iron they need in addition to the N-P-K content.
You may have good results using these targeted blends for specific applications, but for gardens with a variety of decorative or vegetable plants, getting your soil tested before you buy fertilizer is a good idea. You can purchase DIY test kits at garden centers or order them online.
You can also contact your local county extension office and ask them about having your soil tested. The latter will often provide you with more detailed results that include specific recommendations for a fertilizer blend ideal for your area and specific application.
In general, vegetable gardens need some nitrogen, but not nearly as much as your lawn. A good all-purpose garden mix might have an N-P-K ratio of 5-10-10. This mix can produce great results and can be very effective for tomato production in particular.
If you plant bulbs, your best N-P-K ratio will generally have a high phosphorous content and little or no potassium. A ration of 6-12-0 would be fairly typical. Fertilizer mixes for plants grown from bulbs often contain bone meal as well.
There are all-purpose fertilizers, perhaps with a balanced ratio of 10-10-10, intended to promote general flower garden health. But again, a soil test is recommended. Using this mix could harm certain plants if the soil is already rich in nitrogen.
Because plants use more N-P-K than other nutrients, regular application of fertilizer will be necessary to yield the best results. How often you’ll need to fertilize depends on factors such as how much rainfall you’ve had since your last application and whether your soil is naturally rich in nutrients.
Nitrogen tends to wash away in heavy rain. Indications that it’s time to fertilize could include pale leaves, weak stems, plants losing their leaves, and slow growth of lawns and garden plants. Remember, however, that over-fertilization could damage your plants. If in doubt, do a soil test just to be safe.
Organic fertilizers are generally a better choice than synthetics. They actually promote healthy microbial growth and support the earthworm population in the soil. Earthworms aerate the soil and allow more water penetration. They also consume leaves and other organic matter and convert it to even more fertilizer in the form of their castings.
Microorganisms also create more fertilizer by decomposing organic materials. They’re producing compost. Some local and state governments have restrictions regarding the application of fertilizers with high phosphorous content due to concerns about phosphorous runoff contaminating waterways.
Chances are that your local garden supply center would not carry a particular fertilizer blend if its use was prohibited in your area, but, with ordering online being so common now, you may wish to check with your local extension office to find out whether there are any applicable restrictions.
Knowing what the N-P-K ratio represents and how each of these nutrients affect different types of plants will help you choose the right mix for your particular needs. If you know what signs to look for, you’ll also know when it’s time to fertilize.
Getting a soil test will provide more specific information about what N-P-K ratio is best for your soil and the plants you wish to grow. And finally, remember that organic mixes not only provide the nutrients your plants need but also promote microbial growth and the development of a healthy earthworm population – both of which contribute to overall soil health.