When fertilizing the lawn, it's easy to get confused while trying to sort out differences between spreaders and sprayers, slow-release and quick-release fertilizers and amount of application. The first choice you need to make is between a granular (dry) and liquid fertilizer. Granular fertilizers are applied by a spreader; if you don't have a spreader, a liquid fertilizer can be an easy alternative. Liquid fertilizers are generally sold in applicator bottles that simply screw onto the end of the garden hose. If you have a garden hose, you can apply them.
The most common liquid fertilizer for homeowners is a complete fertilizer, which contains the three main essential nutrients that plants need: nitrogen (N), potassium (P), and phosphorus (K). A complete fertilizer allows you to give your plants all the essentials without worrying about individual applications of different types of fertilizer. However, some problems exist with the phosphorus component of the complete fertilizer; because phosphorus can run off into waterways and cause damage, some states have passed laws regulating the application of phosphorus. In Maine, phosphorus application is allowed for lawns in their first year of establishment but restricted to 0 percent for lawns older than one year.
Many homeowners find that they have adequate levels of potassium and phosphorus but lack enough nitrogen, which is easily diminished by water run-off: rain or even watering can cause the nutrients to be carried away to the water stream. This run-off can cause pollution problems; using a slow-release nitrogen fertilizer helps to prevent leaching into the water supply.
A nitrogen-containing fertilizer contains only nitrogen and inactive filler, and avoids the problem of applying too much phosphorus while supplying the essential nitrogen to plants. Nitrogen-containing fertilizers can be quick-release or slow-release. Quick-release fertilizer gives the grass all the nitrogen quickly, and usually results in a dramatic growth spurt and deepening of color in the grass blade. However, quick-release fertilizers can cause leaf burn and need to be applied several times over the course of a year. Slow-release fertilizers provide the nitrogen over a longer amount of time, which means that you won't see the dramatic improvement as quickly, but that the fertilizer will last; generally a once-per-year application of a slow-release fertilizer is sufficient.
Homeowners add iron to their lawns in order to get the sulfur contained in the iron. Sulfur adjusts the pH balance of the soil to a more acidic level. Grass prefers soil that is slightly acidic, but iron is not needed everywhere; it depends on soil type and on the types of plants that have grown previously in the area. Color is a good indicator: if your grass is yellowish, it may indicate a lack of sulfur in the soil. It's best to get your soil tested to be sure; if you need to add iron, several iron-containing liquid fertilizers make the job simple. According to David M. Kopec, a turfgrass specialist, "Iron sources range from insoluble iron (such as ferrous sulfite), quickly soluble but short-lived forms (such as ferrous sulphate), to top-of-the-line chelated (long-lasting iron wrapped in special chemical protecting agents)."