If you go to your local garden department and look through the bags of fertilizer, you’ll find every one of them is making big promises to give you the perfect lawn. But not all lawns are the same, and not all lawns need the same fertilizer.
So it is worthwhile to understand how to buy fertilizer.
The three numbers you see on bags of fertilizer are known as the N-P-K ratio. This lets you know the ratio of nitrogen, phosphorous and potassium (or potash). These numbers are percentages of the total ingredients in the bag of fertilizer.
Now that you know what the three numbers stand for, it’s valuable to know what each of the different ingredients do for your lawn.
Nitrogen is essential for the growth of foliage. It helps to produce lush blades of grass, and if you don’t have enough nitrogen then your grass will have a yellowish tint. It’s important to know that nitrogen is easily flushed through the soil.
Phosphorous stimulates root growth and promotes the development of fruit and flowers. Phosphorous also stays in the ground longer than nitrogen.
Potassium helps plants resist disease and makes plants less susceptible to harsh, changing weather conditions. A lack of potassium can cause weak stems and slow growth. It also flushes easily from the soil, but not as fast as nitrogen.
So how does this help?
Well, an established lawn needs more nitrogen to keep the grass lush. An established lawn doesn’t need as much phosphorous or potassium because it does not need to promote root growth or the development of fruit and flowers and it does not need fast growth.
So when you buy fertilizer for an established lawn, you want a higher ratio of nitrogen. You save money by not paying for phosphorous and potassium you don’t need.
Likewise, a new lawn doesn’t need as much nitrogen because it’s not ready for top growth. With a new lawn, you need more phosphorous and potassium. If your lawn is new sod, you might even want to get a fertilizer blend that has zero nitrogen because the roots on sod have been shaved off and that grass needs to recover. Too much nitrogen on sod, and you could find yourself resodding your lawn.
A stressed lawn – one dealing with winter or extreme heat – needs a fertilizer blend that is high in nitrogen and potassium, so your N-P-K ratio should be big-small-big. This gives the lawn the nutrients it needs in harsh conditions.