Buying fertilizer is not a "one size fits all" proposition. There are many kinds and formulas on the shelves at garden shops and home stores. For maximum growth and health, plants require 16 different nutrients in the right proportion. Knowing some basics will make it easier to be sure you are getting the right product for your needs.
Understand that fertilizer replaces nutrients which are depleted or not available in sufficient supply. Many nutrients, such as nitrogen, are easily leached from the soil when it rains. The two basic types of fertilizer are organic and inorganic. Organic fertilizer is made from living material without added chemicals. Animal manure, compost and crop residues are commonly used. You can purchase organic fertilizer or compost food and plant scraps and make your own. Inorganic fertilizers are commercially made using many chemicals and non-living substances. This is the type that most people are familiar with.
Interpret the numbers on the label to understand the balance of nutrients.All bags of fertilizer have a three-digit number which identifies how much they contain of three key nutrients. A label may say 8-0-24. The first number is the nitrogen, so this bag is 8% nitrogen. The next number represents phosphorus; this bag has none. The third number is potassium, so this formula has 24 percent potassium. If a fourth number is given, it indicates sulfur content.
Select the bag whose formula represents your needs, based on either a soil sample test or specific for what you are growing. There are formulas available that are specifically for tomatoes and other vegetables, roses, and acid-loving plants such as azaleas. If you want a general-purpose formula, look for a 10-10-10 or 5-5-5 mix.It will also be labeled as general-purpose. Flowers like a lot of phosphorus, so look for a middle number that is equal to or higher than the first number. Lawns rely on nitrogen to produce a lush green color, so look for a formula higher in nitrogen.
Buy enough of the selected fertilizer to cover the area needed. The back of the bag will state the approximate number of square feet the bag will cover. Remember, this is an average and will vary according to how heavily your fertilize.
Decide if you want liquid concentrate that is diluted with water, or dry fertilizer. Be sure to read and understand if the fertilizer is applied directly from the bag or must be diluted. Highly concentrated plant formulas will come in smaller and more convenient bottles. Dry lawn fertilizer often comes in bulky bags which can weigh up to 40 pounds.
Dilute (if needed) as directed, when ready to apply. If using dry lawn fertilizer, a spreader makes application much faster and easier. The spreader can be adjusted to how densely you want it fertilized. Apply fertilizer according to directions, keeping pets and children out of the area while applying. Wear gloves and wash hands afterward. Eye protection is also a good idea to protect from splashes or dry fertilizer blowing into the eyes.