Choosing a fertilizer for your landscape can be totally overwhelming. When you look at the shelves in the store, it seems like there is a specific fertilizer for every plant out there – rose fertilizer, lawn fertilizer, houseplant fertilizer, vegetable fertilizer – it can be so intimidating!
To get you started on understanding fertilizers, we need to cover the three main nutrients that fertilizers provide to plants. These are nitrogen (N), phosphorus (P), and potassium (K). Once you understand what each nutrient is doing for your plants, you will be able to choose the best fertilizer for your situation.
N Nitrogen is critical to the growth of new leaves and enhances the green coloration of plants because of its role in the formation of chlorophyll. Chlorophyll is the green pigment in leaves that gives plants their green color and allows photosynthesis to happen. Because nitrogen encourages new growth, you should never use a nitrogen rich fertilizer when a plant is preparing to enter a season of dormancy. This will lead to tender, new growth that will then be damaged by cold or heat and drought, depending on the season.
Nitrogen levels are highly variable in the soil and because of this, they can’t be easily calculated on a soil test. For example, heavy rain will wash a lot of nitrogen from the soil while lawn clippings left in the grass will result a high influx of nitrogen at the time of cutting. For this reason, it’s best to fertilize with nitrogen using a slow-release or organic material such as compost, grass clippings, or manure so that the added nitrogen will not be flushed from the soil as easily and levels may remain more stable. If nitrogen is needed quickly to address a deficiency, consider applying smaller amounts of a quick-release fertilizer to provide plants necessary nutrients while preventing leaching of excess nitrogen. Excess nitrogen leaving the soil can enter water bodies causing algal blooms and other environmental concerns and it is best to limit this when possible.
P Phosphorus promotes flowering and fruiting in plants. Phosphorus is not particularly mobile in plant tissue so plants are not able to absorb and put it to use right away when it is applied as a fertilizer. It is best to build up the phosphorus levels of your soil over time with slow release fertilizers or applications of organic matter such as compost, bone meal, fish meal, or bat guano. Phosphorus is also prone to be leached from the soil which can pollute water sources and interfere with aquatic ecosystems. In some states, it’s illegal to apply phosphorus without a soil test proving an existing deficiency. To best protect the environment, we recommend only applying phosphorus if you have soil test results showing a deficiency or if you’re growing plants for their fruit such as tomatoes, squash, peppers, or melons.
K Potassium is needed for strong root development and for developing the “immune system” of your plants. Plants do not demand as much potassium as they do nitrogen and phosphorus. It’s typical for a balanced fertilizer to contain some potassium. There are not as many environmental concerns related to potassium and the application of a low level of potassium will be just fine in most cases. You definitely want to consider applying potassium when root development is needed such as when laying sod, planting new plants, and transplanting plants.
So how can you tell which and how much of these nutrients are in the fertilizers you are considering buying? Somewhere on the packaging you should see a three number ratio that looks something like these:
10-10-10
16-0-4
19-13-6
These numbers represent the percentage of the fertilizer that is NITROGEN-PHOSPHORUS-POTASSIUM or (N-P-K). When you are thinking about which to purchase, an easy way to remember which nutrient is which and what you are buying for, you can remember the ratio as shoots – fruits – roots. If you don’t have a fruiting plant, buy the one that has a “0” in the second space. If you are trying to green up the plants and grow new leaves, go with a higher number in the first space.
There are all kinds of fancy calculations that can help you take that number and determine exactly how many pounds of each nutrient you are applying when you use that fertilizer at a given rate over a given area… but maybe we’ll save that for another day. For the basics, you just need to know which nutrients are there at all and how much there is of each nutrient in relation to each other. Follow the instructions on the packaging to know how much fertilizer to apply to a given area.
Here’s our breakdown of how we would interpret the three examples given above:
10-10-10
This is considered a balanced fertilizer. We would recommend this only for fruiting plants in a vegetable garden. It is probably too much phosphorus relative to the other numbers for landscape plants and lawn.
16-0-4
This is a good fertilizer for lawns or landscape plants. The higher amount of nitrogen will help green up your plants and promote new leaf growth. This could also be used when planting new plants or laying sod as it contains some potassium for root growth. It does not contain any phosphorus which is just fine as long as we don’t see deficiency symptoms or show deficiency on a soil test.
19-13-6
This fertilizer would be good for flowering landscape plants. The phosphorus it contains will help to promote flowering but it’s still less than the nitrogen provided. The nitrogen will continue to promote healthy new growth.
Check out some of our favorite recommendations for your lawn and landscape below!
Fertilizer for your Lawn
Lawnifi is a subscription service that takes the guess work out of fertilizing your lawn! You will receive seasonal boxes of fertilizers selected specifically for your lawn. We love how easy Lawnifi makes it to take care of feeding your lawn without worrying about what to buy and when. Lawnifi protects the environment in their seasonal boxes by skipping the phosphorus in all of their products and relying on routine, small treatments of quick-release fertilizer, allowing the plants to absorb what they need at the time and minimizing excess runoff. They also sell a new lawn starter-kit that does include some phosphorus to promote growth of the new lawn.
Fertilizer for your Landscape
Nelson Plant Food Color Star is our recommended fertilizer for your flowering plants! The N-P-K ratio is 19-13-6 providing just what your blooming plants need to produce the flowers you love while maintaining healthy leaf growth as well! This fertilizer can be used in containers or in the soil.
