All plants, including grasses, need a steady supply of nutrients to grow properly. Some nutrients come directly from air and water, but we generally supplement some or all of the chemical elements that are essential to healthy grass plants, just as we often supplement minerals and vitamins in our own diets.
Generally a lawn that is not fertilized regularly will look pale and growth may be sparse. If the grass becomes dormant or it is damaged in any way it will be more susceptible to disease or weed attack, and it will take longer to recover.
What you need to know about fertilizing lawns
There are 16 chemical elements that grasses need and these may be divided into four groups. These are:
- The natural elements found in the air or in water: carbon, hydrogen and oxygen. We, of course inhale oxygen and exhale carbon dioxide which plants then take in.
- Vital macronutrients, specifically nitrogen, phosphorus and potassium that make up between 6 and 11% of the dry weight of lawn grasses.
- Secondary elements which are also essential to the life of grass, namely calcium, magnesium and sulfur.
- Micronutrients or trace elements that are present in minute amounts, but are also very important. These include iron, manganese, zinc, copper, molybdenum, boron and chloride.
The various types of fertilizer contain certain quantities of these nutrients and elements in various proportions, depending on the formulation and what it is intended to achieve. Always look for an indication of the ratio in which nitrogen, phosphorus and potassium occur. For example if you see 25-10-30 you know that there is a quarter pound of nitrogen for each pound of fertilizer, but only 10 lb. of phosphorous and 30 lb. of potassium included in the fertilizer mix.
Nitrogen makes grass grow fast and helps it turn a lush, green color. It also helps the grass tolerate heat, cold, drought and general wear and tear by keeping it healthy.
Phosphorus helps to establish a strong, deep root system that will help make the grass resistant to general stress, including spells of dry weather. It also aids seed germination.
Potassium contributes to photosynthesis which is the process plants use to turn sunlight into energy. It also toughens grass and, like nitrogen, helps it tolerate heat, cold, drought and general wear and tear.
Different kinds of fertilizer for lawn
There are so many different types of fertilizer it can be mind boggling, especially if you don’t know exactly what it is your lawn needs. In general terms we can categorize fertilizers as either being liquid or granular, but there are also quick-release fertilizers, slow-release fertilizers and controlled release fertilizers. Then there are also fertilizers that contain herbicide as well as both organic and natural fertilizers.
Liquid fertilizers take more time to apply than other types, and they are generally more difficult to spread.
Granular fertilizers, which are dry, are popular because they can be measured out easily, quickly and accurately and they are easy to spread effectively using a broadcast spreader. These spreaders come in various sizes and different models, including those that you can attach to a rider mower if you have one.
When a granular fertilizer states that it is ‘homogeneous’ this means that each fertilizer pellet or grain contains all the nutrients that are specified on the label. This also means that the proportions of nitrogen, phosphorus and potassium are exactly the same in every single pellet. Cheaper fertilizers that are not homogeneous are not accurately manufactured and so you won’t be sure that the different ingredients are being evenly distributed over your lawn.
Fertilizers with herbicide are designed to kill off certain kinds of broadleaf weeds. There are also fertilizers with that contain pesticides. Read the label information carefully and make sure you follow the guidelines. For example you need to be aware of how many dry days you need for some products to be effective. Also make sure you are using the right herbicide for the weeds in your grass. Most products are quite specific in this way.
You should also check your local regulations because in some areas only licensed applicators are allowed to spread fertilizers that contain herbicides, while others require you to get a special permit.
If you go here you will find out all about preventing pollution problems that can occur if you use lawn and garden fertilizers.
Organic fertilizers (or more correctly synthetic organic fertilizers) are made up of a combination of organic compounds, carbon for example. Truly organic fertilizers are natural fertilizers including alfalfa meal (3-3-2), bat guano (10-4-1), blood meal (10-1-0), bone meal (0-4-1), castor oil meal (5-1-1), composted cow manure (1-1-1), cottonseed meal (7-2-1), feather meal (11-0-0), fish meal (10-4-4), hoof and horn meal (12-2-0), poultry manure (4-4-1), rock phosphate (0-3-0), sea weed (1-0-4 plus more than 50 important elements), and wood ash that is high in potassium and various micronutrients.
Commercial mushroom compost as well as homemade compost can also be used to fertilize lawns, as can horse manure that has been left to stand and rot naturally for several months. All types make an excellent organic fertilizer.
Timing is not as important with natural fertilizers as it is when you use chemical fertilizers and they generally don’t ‘burn’ the grass. They are also completely environmentally friendly.
Fertilizing new lawns
Before you plant a new lawn you should always ensure that the soil is the best quality possible and suitable for the particular grass you are going to plant. This involves testing the pH of the soil to make sure it is neither too acid nor too alkaline. Most plants prefer slightly acid soil – most grasses like it to be either neutral (7.0 on the pH scale) or slightly acid (6.0).
Organic matter (compost for example) will improve any type of soil, and it is best to add this before you seed or plant lawns. Also add a fertilizer recommended for the grass you are going to plant. This should be done prior to seeding or planting.
Allow seed to germinate and the plants to establish themselves before you even consider fertilizing a new lawn. If you have planted sods, don’t fertilize for at least the first six weeks.
Fertilizing established lawns
While grass type as well as region and the maintenance level required will all help determine the schedule and frequency required for fertilizing, it is usually a good idea to fertilize once or twice in the fall. Then fertilize cool-season grasses again in early spring and warm-season grasses again mid-spring.
There are various different options, but you could use a high-nitrogen lawn fertilizer in which at least half of the nitrogen is slow release.
Lawn fertilizing tips
- Most grasses benefit from being fertilized three or four times a year.
- Fertilizing in fall helps to prepare lawn for the winter.
- All grasses need a certain amount of nitrogen every year. Use the requirements shown in the table below to work out your fertilizer program.
|Type of grass
|Variety of grass
|Lbs nitrogen required *
*The number of pounds of actual nitrogen that should be applied to 1000 square feet over one entire year.