In general, fertilizer is a material designed to release nutrients and give a plant the elements it needs to grow. The two most common examples of fertilizer for plants around the home are:
- Lawn fertilizer, such as one that nourishes fescue or Bermuda grass
- Plant food, such as one designed to make the most of roses or boost the yield of vegetables, such as tomatoes or asparagus
You might use a fertilizer if the soil is lacking some of the necessary elements, or if the elements have been depleted over time. Fertilizer is designed with natural or synthetic ingredients that supply these elements in a form that’s easy for plants to take in.
Nutrients in Fertilizer
All plants need several types of nutrients, and some need them in large quantities. Nutrients that may not be easily available in soil in the right amount are the primary ones you find in fertilizer:
- Nitrogen for plant growth, leaf development and the production of vivid, green color
- Phosphorous for root growth and the creation of fruit, seeds and flowers
- Potassium, sometimes called potash, for root development and resistance to drought and disease
Secondary nutrients — oxygen, carbon, hydrogen, calcium, magnesium and sulfur — are also essential macronutrients that are often available in soil or air.
Micronutrients — including boron, chlorine, cobalt, copper, iron, manganese, molybdenum, nickel and zinc — are needed only in small amounts.
Before you shop for fertilizer, perform a soil test. You can purchase a home test kit or send a soil sample to your local cooperative extension office for testing. The results will tell you what to add to the soil to make it ideal for the plants you plan to grow.
How to Read Fertilizer Numbers
Three prominent numbers on a fertilizer package (known as the NPK value, guaranteed analysis or fertilizer grade) tell you the percentage of available primary macronutrients by weight in the package:
- Nitrogen (N) content is the first number.
- Phosphorous (P) content is the second number.
- Potassium (K) content is the third number.
A fertilizer label marked with 18-24-6 contains 18% nitrogen, 24% phosphorous and 6% potassium. To determine how much of each is in the bag, multiply the percentage by the weight of the bag. For example, for a 50-pound bag, you’d do the following calculations:
0.18 x 50 = 9
0.24 x 50 = 12
0.06 x 50 = 3
The bag contains 9 pounds of nitrogen, 12 pounds of phosphorus and 3 pounds of potassium. The remainder is typically inert material, which helps evenly distribute the fertilizer and prevent chemical burns. There may also be secondary nutrients or micronutrients in the formula.
Fertilizer Application Methods
All lawns are different, so you’ll want to select the best fertilizer for your needs. Apply granular fertilizers dry — with a mechanical spreader or shaker container — and then water them in. Lawn and garden fertilizers are often in granular form. They’re easier to control because you can see how much you’re using and where you’re dispersing them. There are two formulations of granular fertilizers:
- Quick-release fertilizers — known as water-soluble nitrogen (WSN) — provide nitrogen to plants immediately. They generally last for three to four weeks, depending on temperature and rainfall.
- Slow-release fertilizers — or water-insoluble nitrogen (WIN) — are available in sulfur-coated varieties, which last for about eight weeks, and polymer-coated varieties, which can last for about 12 weeks. The time estimates may vary depending on the amount of rainfall. You don’t need to apply these fertilizers as often, and they produce more even growth. In addition, burning caused by nitrogen is less of a concern with slow-release fertilizers.
Liquid fertilizers are fast acting. Plants absorb liquid fertilizer quickly through the leaves or roots, so you need to apply them every two to three weeks. Most are concentrates you mix with water. Some are available as hose-end bottles that create the mixture as you apply them, but you can also mix it yourself and apply with a watering can. Liquid fertilizers work well for container plants, and you can also find liquid lawn fertilizers.
Plant food spikes are a solid form of fertilizer you drive into the soil to dispense nutrients over time. They provide a simple means to feed house plants, trees and shrubs.
Subscriptions: Sign up for our subscription service to save on fertilizer. It’s free, and you can pause or cancel anytime.
Annual Programs: With our annual program, you’ll always have the right fertilizer on hand for spring, late spring, summer, fall or winter. You can also purchase bags separately.
Lawns have specific fertilizer requirements, depending on the season and the type of turfgrass. Read the instructions on the package carefully to make sure it's formulated for your lawn. The packaging also gives you the square footage the product will cover and spreader settings to apply it at the correct rate. 10 10 10 fertilizer is a fast-release, all-purpose formulation that can be used on lawns as well as flower beds and vegetable gardens. See Fertilize Your Lawn for instructions on feeding turfgrass.
Weed and feed is a lawn fertilizer that contains weed killer for broadleaf weeds (such as dandelions) or grassy weeds (such as crabgrass). Look on the label for a list of weeds that the product is effective against to be sure it fits your needs. Applying these products at the proper time is necessary for success. Pre-emergents, such as those commonly used to prevent crabgrass, are weed killers that you apply early in the season, before weeds germinate. They're ineffective if the weeds are already growing. Post-emergents kill actively growing weeds on contact but don't kill weeds that haven't germinated. If you're also sowing grass seed, check the weed and feed packaging for the proper interval between applying weed and feed along with sowing seed. Weed-control products can prevent germination or kill immature grass seedlings.
There are two other special formulations you may see. Winterizers are fertilizers with high levels of potassium to help cool-season lawns deal with the stress of winter. Starter fertilizers have high levels of phosphorous to help new lawns develop strong roots. You can also find lawn fertilizer designed to provide insect control as it feeds.
Fertilizers for vegetables, flowers, trees and shrubs are often known as plant food. They're available as liquids, granules or spikes. You'll find some for general use and others specially formulated for indoor plants (African violets and cacti) or outdoor plants (roses, rhododendrons and evergreen trees). Some plant food includes weed control. Read the label to see which weeds they're effective against. Look for packaged soil mixes that include plant food as well as elements to improve water retention and aeration. Some plant food isn't suitable for edible plants.
While fertilizers can benefit plants, they can create problems and cause damage if overapplied and if they enter waterways, such as streams or rivers. Since correct application is necessary, be careful and always follow application instructions.
Natural Fertilizer Alternatives
Many people choose to use organic fertilizer, natural soil conditioners and soil additives. Some of the most common are:
- Blood Meal: A byproduct of the meatpacking industry. Steamed and dried, it's high in phosphorous.
- Bone Meal: Another byproduct of the meatpacking industry, bone meal contains calcium and phosphorous, essential elements for plant growth.
- Fish Emulsion: A fish-processing byproduct. Mild, nontoxic and organic, fish emulsion is good for tender plants that may suffer fertilizer burn.
- Compost: One of the best all-around garden fertilizer materials for soil improvement.
- Composted Manure: For soil conditioning or use in the compost pile.
- Peat Moss: An amendment that aerates and lightens heavier soils such as clay. It adds mass to sandy soils to reduce the leaching of nutrients.