15-0-15 fertilizer contains high levels of nitrogen and potassium, with no phosphorus. It promotes strong grass blade growth and aids your lawn in disease resistance. However, it may not be perfect for all lawns. Is 15-0-15 fertilizer good? Is it ideal for your species of grass? If so, when and how should you apply it?
- 15-0-15 can be extremely beneficial for your lawn when used correctly.
- 15-0-15 is great for established warm-season grass lawns.
- 15-0-15 fertilizer should be spread from spring through summer.
By using 15-0-15 fertilizer at the right time, in the right manner, you boost your lawn’s performance and health. If it’s used at the wrong time, or on the wrong lawn, it may not be as beneficial. It’s important to assess if 15-0-15 is right for you.
What do the Numbers on 15-0-15 Fertilizer Labels Mean?
Fertilizer labels contain 3 numbers, separated by dashes, such as in the case of 15-0-15. These numbers always refer to the same ingredients in this order:
Number 1: Nitrogen percentage
Number 2: Phosphorus percentage
Number 3: Potassium percentage
In the case of 15-0-15 fertilizer, these numbers signal that the fertilizer you’re considering contains the following:
- 15% Nitrogen
- 0% Phosphorus
- 15% Potassium
That still leaves 70% of the bag that isn’t contained within these 3 numbers. This 70% may include small percentages of other nutrients, such as iron, manganese, and zinc, which will be listed on the label. The rest of the fertilizer is made up of filler ingredients that aid distribution and soil absorption.
What Nutrients Does Your Lawn Need?
Let’s examine fertilizer contents more closely, now that we know what the numbers stand for. Here’s a handy breakdown of the benefits of the 3 key fertilizer ingredients.
- Nitrogen: Drives grass blade growth and provides the green color.
- Phosphorus: Helps establish new, young root systems.
- Potassium: Strengthens your lawn against disease, drought, and cold.
Now that we have this understanding, we can begin to examine 15-0-15 fertilizer and determine if it’s right for your lawn.
What is 15-0-15 Fertilizer Used For?
Due to its high nitrogen and potassium content, 15-0-15 fertilizer is ideal for promoting the health, color, and growth of established lawns. New lawns grown from seed or sod require a fertilizer with high phosphorus because this nutrient encourages young root growth. For a new lawn, a fertilizer with a ratio of 10-18-10 would be better.
15-0-15 fertilizer can be used on many grass types, but it has the best results when applied to warm-season grasses such as Bermuda, St. Augustine, Zoysia, and Centipede. These grasses are typically fast-growing, so they need high levels of nitrogen in 15-0-15 to support rapid growth. These grasses are also often exposed to drought and/or disease, so the high percentage of potassium is key for disease resistance.
When Should You Use 15-0-15 Fertilizer?
Spring
One of the best times to apply 15-0-15 is in spring, just as your grass exits dormancy. If you live in a region where your grass doesn’t go dormant in winter, application in April–May is ideal.
Summer
Fast-growing warm-season grasses like Bermuda, Centipede, and Zoysia will grow well into summer and consume large amounts of nitrogen to fuel growth. For this reason, it’s best to follow up spring applications with additional 15-0-15 fertilizer in summer.
Fall/Winter
Avoid using 15-0-15 fertilizer in fall and winter. As summer comes to a close, consider using a gentler fertilizer with little or no nitrogen content in many cases. In most regions, winters cause grass growth to slow or stop. Little or no fertilization is required in winter, as a gentle fall fertilizer should carry your lawn through the cold months.
Using 15-0-15 Fertilizer on Various Grass Types
Although 15-0-15 fertilizer has some success when applied to cold season ryes and fescues, it is best suited for warm-season grasses. Tailor your application for the grass in your lawn.
Bermuda
According to Clemson University, Bermuda grass performs best when fertilized with high-nitrogen fertilizer in May through August. Plan to apply 15-0-15 in multiple applications through the growing season (May-August). 15-0-15 on Bermuda lawns is best split into 3 stages:
- Spring: 50 lbs of 15-0-15 for every 7,500–15,000 square feet of lawn.
- Mid-Summer: 50 lbs of 15-0-15 for every 7,500–15,000 square feet of lawn.
- Late-Summer: 50 lbs of 15-0-15 for every 7,500–15,000 square feet of lawn.
Zoysia
Zoysia grass thrives on even higher nitrogen levels than Bermuda. Ideally, 2–4 pounds of Nitrogen should be applied to Zoysia lawns in May-August. Here is the breakdown for 15-0-15 fertilizer on Zoysia lawns.
- Spring: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
- Mid-Summer: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
- Late-Summer: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
St. Augustine
St. Augustine grass can have similar nitrogen needs to Zoysia grass (2–4 lbs of nitrogen), depending on the soil type. If you have sandy soil, you will need more 15-0-15 on St. Augustine. If you have clay soil, you will need less fertilizer. Also, while sandy soil requires 3 fertilizations over summer, clay soil lawns only need 2 stages of fertilization.
Sandy Soil
- Spring: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
- Mid-Summer: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
- Late-Summer: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
Clay Soil
- Spring: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
- Mid-Summer: 50 lbs of 15-0-15 for every 7,500 square feet of lawn.
Centipede Grass
15-0-15 is great on Centipede grass because Centipede lawns do not require phosphorus. Centipede grass also thrives on less fertilizer than many other warm-season grass types. Below is the optimal schedule for using 15-0-15 fertilizer on Centipede grass.
- Spring: 50 lbs of 15-0-15 for every 7,500–15,000 square feet of lawn.
- Late-Summer: 50 lbs of 15-0-15 for every 7,500–15,000 square feet of lawn.
Can You Use 15-0-15 in a Vegetable Garden?
Most garden plants thrive on nitrogen and potassium, just like your lawn grasses do. 15-0-15 is a great vegetable garden fertilizer. It can even be applied year-round in vegetable gardens to feed the soil and promote plant growth. In fact, when fertilizing your lawn, it’s a good idea to just expand your range and spread 15-0-15 in your garden as well.
It’s important that you don’t overload your soil with fertilizer, as this can lead to plant dehydration. Apply 15-0-15 to your vegetable garden at the rates recommended on the bag, and apply no more than 3–4 times per year.
15-0-15 Fertilizer and When to Use It
15-0-15 fertilizer is a very powerful fertilizer that is designed to contribute to the growth, color, and disease resistance of established warm-season grasses. It is best used on grasses such as Bermuda, Zoysia, St. Augustine, and Centipede. Apply 15-0-15 to your established lawn in 2–3 applications from spring through summer for best results.
Avoid using 15-0-15 on new lawns started from sod or seed, as these require a fertilizer with phosphorus for new root growth (the 0 in 15-0-15 stands for 0% phosphorus). Also, 15-0-15 is not the best fertilizer for most cold season grasses. If your lawn is primarily Rye, Fescue, or Kentucky Bluegrass, there are several other ideal fertilizers for cold-season grasses.