As spring starts to appear, attention often turns to our gardens. Roberts sends in a good question about applying a spring lawn feed to his grass. He writes:
I am looking to apply a spring granular feed to my one acre lawn. What NPK analysis numbers would you recommend please?Robert, By email.
Thanks for the question Robert. You may think that a simple question would require a quick answer. As with many lawn care issues, the deeper you explore, the more complex the issue becomes.
Firstly, I’ll quickly explain a little about what is meant by NPK analysis numbers. NPK is the standardised labelling notation used on fertilisers. N, P and K are the chemical element symbols for Nitrogen, Phosphorus and Potassium (it is a K which stands for, Kalium in latin). These are the main elements required for all plant growth. NPK fertilisers are called “three component” fertilisers. They contain a proportion of each of these main elements.
The NPK value of a fertiliser is given in the form of three numbers which indicate the contents. e.g. NPK 20-7-12. That would indicate that the product contains 20% Nitrogen, 7% Phosphorus and 12% Potassium. This is a simplistic summary of a very complex topic, but good enough as a guide for most.
Using the NPK analysis is a quick and easy way to assess how and when the fertiliser should be used.
Spring lawn feed NPK analysis
Add Nitrogen (N) to promote leaf growth
In spring, plants are looking to put on new leaf growth as soon as possible. For this they need Nitrogen. This is why spring lawn feeds contain higher percentages of N.
Be careful to not over-apply Nitrogen though. Imagine you had not eaten anything for a week. Then the first thing you ate was three huge meals -you’d feel a bit sick. This is the same with grass. Overfeeding can be just as bad as underfeeding. Little and often is always best when applying most lawn nutrients, especially Nitrogen.
Phosphorus is one of the key elements in plant growth but it is less needed during spring time. It is mainly required to support cell division in plants and to help young plants establish a good root system. For an established lawn, only a small amount of P is needed in the spring lawn feed.
Potassium (K) in a wet winter
The next main element which will be needed in spring is Potassium (the K part of NPK). In grass it is an essential element for root growth. The Potassium molecules are very small and dissolve easily in water. Heavy rains wash potassium out of soil quickly and plants then struggle to find it when coming into spring growth.
Adding Potassium in the spring or applying gradually throughout the winter, will improve the look of your grass in the summer.
Which NPK for a spring lawn feed?
In summary, a good spring lawn feed need high N, low P and a high K. something like a 20-2-12 granular lawn feed is ideal. A soil test in the spring would also be good way to identify any nutrient deficiencies in the soil, and you could modify the feed to rectify any deficiencies. However, for most lawns, a high N, high K balanced spring lawn feed will bring give great results.
You could apply this as a liquid or as a granule. Read more about the differences between the two in my post: Liquid or granule lawn fertiliser?
Feed your lawn little and often, mow high and regularly and you will have a fabulous lawn for the summer.