15-0-15 Fertilizer: What’s It All About?

One of the most thrilling things about gardening is having a lush, green lawn to complement all your plants and flowers.

In addition to a sensible watering regime, you’ll also want to get yourself the best fertilizer for the job.

Today, we’ll take a look at what the numbers like 15-0-15 displayed on the packs of fertilizer mean along with some general tips and guidance on fertilizing your lawn the right way.

The right nutrients are paramount if you want to get the very best out of your lawn.

What Do The Numbers Mean On Fertilizer Packs?

15 0 15 fertilizer

Source: Woerner Landscape Services

When you look at packs of fertilizer, you’ll see 3 numbers quite prominently displayed.

These numbers refer to:

  • Nitrogen
  • Phosphorus
  • Potassium

Your lawn needs plenty of nitrogen so that you’ll get proper growth, a perfect color and overall health to your grass. Warm-season and cool-season grasses both respond well to a slow-release fertilizer rich in nitrogen.

Phosphorus helps to kickstart early growth. This is crucial for your seedlings to develop correctly. If your lawn has been freshly seeded, you should opt for a mix heavy in phosphorus.

You’ll want potassium in your fertilizer to help build up resistance to disease and to add strength to the root structure.

The numbers will always be listed in this order (nitrogen, phosphorus, potassium) and illustrate the percentage of each component found in the pack.

A 10-10-10 mix is a very common all-purpose garden fertilizer. To break it down, if you got a 50-pound bag you would have 5 pounds (10%) of nitrogen, phosphorus and potassium. The remaining 70% of the bag is made up of inert filler to help get the chemicals circulating efficiently.

Using 15-0-15 Fertilizer


SourceWoerner Landscape Services

If you go for a mix of 15-0-15, you’ll have nitrogen and potassium but no phosphorus.

Warm season grasses like Bermuda and St Agustine respond well to this mix. From shrubs and trees through to ornamental gardens or vegetable patches, 15-0-15 has a range of applications.

The ideal time to apply 15 0 15 fertilizer is from the middle of spring on through the summer. You can use it year-round with no problem at all.

Apply it with a spreader, mix lightly and water thoroughly.

Types of Fertilizer

You have a choice of several different types of fertilizer over and beyond the mixes listed above.


This type of fertilizer does not need to be used as frequently. The trade-off is that it’s usually much more expensive.


If you want results in a hurry, fast-release fertilizer will deliver.

You’ll need to apply this fertilizer more often and using lesser amounts. Be very cautious not to use too much or you might burn your lawn.

Liquid Fertilizer

These are tough to apply evenly and need to be regularly re-applied so are best avoided.

Organic Materials

Compost and manure are not as concentrated as chemical fertilizers so you’ll need to use a great deal more.

Be very careful with horse manure as it can contain weed seeds.

When To Fertilize Your Lawn


Source: Pike Nursery

You should ideally fertilize your lawn three times a year.

It’s absolutely essential to feed your lawn while it’s still activelt growing and never during a period of drought.

Start off in early spring as the grass starts to get green.

From that point, your fertilizing schedule will depend on 3 main factors:

  • Climate
  • Type of grass
  • Type of fertilizer

Most lawn seed that you get is a mixture of a few types of grass so fertilizing in spring and fall is advisable.

If there is any kind of drought, either stop using fertilizer or cut it right back. In these conditions, you want to lessen the amount of nutrients your lawn gets so growth will slow back. Reduce watering too if things are too dry for comfort.

How To Fertilize Your Lawn


Source: Curbed Seattle

You can fertilize by hand but the results are questionable. You risk burning the grass if you apply it in too concentrated a manner. If you miss covering other areas adequately, you’ll get pale patches.

The best option is to buy yourself a fertilizer spreader. We reviewed some of the best fertilizer spreaders here.

  • Apply your chosen fertilizer to freshly mown grass. Make sure there is no wind although a fine dew is OK
  • For best results, use only half the suggested amount in your spreader
  • Remember to start working before you turn on your spreader and to shut it down before you come to a stop
  • Make sure you wash your spreader after use
  • Water the lawn for optimum effect. It’s perfect if you can fertilize just before it starts raining but if not then just thoroughly water instead

Is It Possible To Use Too Much Fertilizer?


While making sure your lawn gets the added nutrients it dearly needs is wise, being heavy-handed with your fertilizer can lead to problems.

Using too much feed will mean you need to mow your grass far more often.

The grass also tends to grow back quickly so, if this happens, make certain to obey the one-third rule: don’t cut off more than one-third of the leaf blade in one session of mowing. If you end up scalping the lawn, you’re inviting the weeds in.

Also, over-fertilizing can lead to turfgrass diseases setting in. Both pythium and brown patch take root in warm and moist conditions where over-fertilization has occurred. You’ll need some fungicide to fight back if these diseases take hold.

If you go totally over the top and grossly exceed the recommended application rate, you’ll finish up with scorched yellow grass and a ruined lawn.

The key? Less is more with fertilizing.


Well, hopefully you have enjoyed our explanation of 15-0-15 fertilizer and you now have a clear idea of what the numbers on fertilizer packages translate to.

Please feel free to share any of our articles on your social media if you think they would be of interest.

Contact us at any time if you have any questions or there’s anything you’d like to know about any aspect of gardening.

Now get that fertilizer spreader going!

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