While you don’t need a fancy fertilizer to have a beautiful yard, it really is a quick and easy way to get that lush lawn you’ve always wanted. Of course you can start composting, researching minerals and then finding organic matter to spread on your yard, but this can be both expensive and time consuming. Store-bought fertilizer is a much faster and easier way, and the calculation of mineral content has already been done for you. The key is to choose the right fertilizer and apply it in the correct way to get the results you want.
How & When to Fertilize
How do I read a fertilizer bag or bottle?
When you shop for fertilizer at any home and garden store, you’ll see a series of numbers listed on the label, but what do they mean? Identifications like 20-20-20, 10-8-10 or 10-10-10 can leave your head spinning if you don’t know what these numbers mean.
These numbers are known as the NPK values of the fertilizer. In other words, it gives you the breakdown of the main ingredients and their proportions. “N” stands for nitrogen, “P” stands for phosphorus or phosphates and “K” indicates potassium. These are the three many ingredients in any commercial fertilizer (see below). When you see the numbers listed, the fist number stands for “N”, the second for “P” and the third for “K”, so a 10-8-10 mix has 10 nitrogen, 8 phosphorus and 10 potassium.
In regards to the numerical values, the higher the number, the more concentrated that element is in the mix. For instance, if a label says 20-20-20, it has twice the concentration of all three nutrients than a 10-10-10 mix. If it says 20-5-5, that means it has four times more nitrogen than it has phosphorus and potassium.
These numbers are used to figure out how much you need to put into the soil to equal one pound of each nutrient. So, if the number is 10, that means you would divide100 by 10 (=10) to see that using 10 pounds of fertilizer will add 1 pound of that nutrient to the soil. If it’s a 20-20-20 mix, it takes 5 pounds of the fertilizer to add 1 pound of each nutrient to the soil.
If you see a zero in the mix, it means it’s just not in there, so a 10-0-0 mix only contains nitrogen.
Should I get liquid or dry?
Generally these do the same job, so it’s usually a matter of convenience which one you choose. Liquid fertilizer act very quickly, as they don’t need to be broken down in the soil. They are quickly absorbed by plants, so you’ll need to apply them often (pay attention to the package directions). Some are concentrated and need to be mixed with water, and some you can use with a container attached to your garden hose. Liquid fertilizers can be used on the lawn, but they’re most popularly used on container plants.
Granule (or dry) fertilizers are either shaken or spread and then need to have water added on top. Lawn and garden fertilizers often come in this form. One plus is that they’re easier to control than the liquid variety, as you can see exactly how much you’re using.
One other type of dry fertilizer is plant food spikes. These are solid fertilizer sticks that you push down into the soil, and they release nutrients over time. They are simple and less messy and work great for house plants.
What are the main ingredients in fertilizer?
Nitrogen is the main ingredient in fertilizer, and its job is to promote growth of the overall grass shoot. You’ll see the nitrogen content marked on the package with an “N” followed by a percentage. This shows the total percentage of nitrogen in the mix.
However, the percentage isn’t nearly as important as the quality of the nitrogen included; meaning what form it’s in. Nitrogen in fertilizer comes in three forms:
Fast Release Nitrogen
These types are also called soluble nitrogen because of the way they release nutrients into the soil. Some examples of these are ammonium sulfate, ammonium nitrate, urea, stabilized urea and calcium nitrate. True to their name, they release nitrogen quickly into the soil. Typically, all of their nutrients are released into the ground within one week of application, and many of them get the job done within 24 hours. You will typically see a change in your plants from this type within a few weeks after applying it.
One important thing to be aware of using these however, is that since they release so quickly, the application rate is important. Otherwise, you could see excessive growth of grass shoots and possibly leaching of urea and / or nitrate since these are both water soluble.
With this type of fertilizer, several applications are usually necessary since they release so quickly and don’t last very long. Applying regularly is necessary to maintain the quality of the grass over time.
Slow Release Nitrogen
Slow release, also known as time release nitrogen is common in retail fertilizers. Just like a time-release allergy pill, its job is to give an initial blast of content right away, then to release the rest more slowly over time. This is important because if too much nitrogen is put onto the grass all at one time, it can cause the top of the grass to grow excessively, which puts the grass under stress. It can also result in leaching, meaning more nutrients can be lost from the soil or washed away when it rains.
There are different types of slow release nitrogen. While different companies give them different trade names, they all break down into either synthetic reacted organics, polymer coated sulfur coated urea or natural organic fertilizers.
Synthetic reacted organics are also known as urea formaldehyde fertilizers. These types are made from chemical reactions that are designed to mimic nature. They are formed by the reaction of formaldehyde with urea, making U:F polymers. They then release by microbial mineralization or feeding, just like organic fertilizers.
Some brand names of synthetic reacted organics you might recognize are Triazone, Sazolene, Coron, BCMU, MU, MethEx, Nutralene and Nitroform. The fertilizers include three fractions of nitrogen from the process of manufacturing. The balance of three nitrogen fractions is determined by the amount of formaldehyde to urea and the length of the reaction time. The three fractions are Hot Water Insoluble Nitrogen, Hot Water Soluble Nitrogen and Cold Water Soluble Nitrogen. They are abbreviated as HWIN, HWSN and CWSN respectively.
On a product label, you’ll see WIN (water insoluble nitrogen), which is made up of the total amount of HWIN and HWSN. The CWSN fraction is known as quick release, because it releases completely within two weeks after being applied. HWSN is hot water soluble and releases within two to three months. HWIN releases over several months or years and is not soluble in boiling water. The amount of time it takes to release depends on environmental conditions and climate.
The second kind of slow release nitrogen is PCSCU (polymer coated sulfur coated urea). Some brand names include XCU, PolyPlus and PolyS are examples of these types. In these types, nitrogen release is based on water. In order for the nitrogen to be released, water must absorb through the layers of the coatings around the urea substrate. The rate of absorption and speed of release are determined by the thickness of the coating and the amount of water to which it is exposed.
When water absorbs through the outer coating, it saturates the urea substrate inside. Urea is fairly water soluble, so it dissolves quickly. Once it is dissolved, an osmotic pressure gradient is created, and it’s relative to the dissolved urea concentration inside versus outside the granule. If the pressure inside is too excessive, the coating explodes, known as catastrophic release. How slow nitrogen releases is determined by the thickness of the coating.
The last form of slow release nitrogen is natural organic fertilizer. These release nitrogen when they are fed on by microbes or mineralized. It’s essentially the same process you would see over time in a compost pile. The release of nitrogen is a bit unpredictable and can accumulate over time depending on how often it is applied.
Timing is also important and should be considered depending on if you have warm or cold season turf grass. More nitrogen in these fertilizers tends to be released in the warmer part of the year, which may not do you much good if you have cool season grass.
Controlled Release Nitrogen
These are also known as polymer or resin coated types of fertilizer. In manufacturing, a fast-release substrate of nitrogen is coated with a polymer or resin coating. One example of a resin coated fertilizer is Osmocote, which release via osmosis. Polyon is a polymer-coated product, and the polymer coating acts like a membrane. Nitrogen is release when water dissolves the outer coating, and nitrogen diffuses out of the underlying granule. How thick the coating is will determine how fast or slow nutrients are released.
Having phosphates in fertilizer is very important because this ingredient helps your plants and grass to convert other nutrients into usable elements. It’s identified by a “P” on any fertilizer bag or bottle.
As far as commercial fertilizers, you may see phosphates broken down by water soluble, citrate soluble and available. Water soluble mean the fertilizer is placed in water in a lab, and a measurement is taken of the percentage of the total phosphate dissolved. Citrate soluble is not dissolved in water. Rather, it is put into a solution of ammonium citrate. Then, the amount of phosphate dissolved is measured. Available refers to the total sum of the citrate and water soluble properties.
Sources of Organic Phosphorus
Organic sources of phosphorus can include animal manure, compost and sewage sludge. If you see organic on a bag of fertilizer for the phosphate content, it generally means there are organic as well as inorganic sources. All the inorganic will be in the orthophosphate form (the form taken by plants that are growing). The chemical makeup is also determined by the diet fed to the animals from which the manure is collected. Generally speaking, about 45-70% of the makeup of manure will be inorganic.
Many people wonder if it’s better to buy dry or liquid fertilizer. In this case, the amount of phosphorus your plants or grass can utilize isn’t dependent on whether the fertilizer is in dry or liquid form. It will be more affected by climate conditions, characteristics of root growth and the amount of water in the soil.
Sometimes you’ll see phosphate listed as polyphosphate or orthophosphate. Orthophosphate is an ester or salt of orthophosphoric acid, whereas polyphosphate are esters or salts of polymeric oxanions. While this may seem like difference may seem like gibberish to most users, it breaks down like this: Polyphosphates have water taken out in the manufacturing process, so they have a higher analysis than those in the orthophosphate form. They’re also more convenient to handle and allow more blends to be formulated than with orthophosphate.
In regards to buying fertilizer, that second number really can’t be too high and for most homeowners, the type of phosphate used won’t make that much of a difference in their lawn, if any. It can be hard for plants to absorb phosphorus, so “too much” is okay no matter the type. The only time this would be a concern is if you’ve had your soil analyzed and already know it’s very high in phosphorous.
Potash is simply another term for fertilizer potassium. Potash in early production was leached from concentrated leached wood ashes and was made in large iron pots (thus pot-ash). While it’s no longer done this way, the name has still stuck.
Potash is widely available in modern form and is the seventh most common natural element. It’s harvested as salt deposits from being store in soil. In fertilizer, the form potash usually takes is as sulfates, chlorides and nitrates. When these are used by plants, potassium is released.
Potassium in plants is essential to synthesize plant sugars for them to use as food, and it’s also essential for the uptake of water. High levels of potassium can produce a higher quantity of flowers of better quality.
If you have soil with an alkaline pH, using potash is crucial, as it increases the soil pH. However, if you have plants that love acid like rhododendrons, azaleas or hydrangeas, you can have problems if too much potash is used. Before using too much potash, it’s important to have your soil tested to see if it’s deficient in potassium.
If you’re composting, you can add wood ash to your compost to up the potassium. Manure can also be used because it naturally has potassium in a small percentage, and it’s easy on plant roots. Greensand and kelp are also good sources.
When using potash, it’s good to know that it doesn’t move more than an inch or so from where you put it, so it’s best to till it directly into the soil. If you have potassium-poor soil, ¼ – 1/3 pound of potassium sulphate or chloride per 100 square feet should suffice.