Why Do Grass Feed NPK Values Vary So Much Between Manufacturers?

b3n.doyle

Hey guy's,

It's just a curiosity for me.

I understand the need to change the NPK value of a lawn feed depending on the time of year.

But taking spring/summer lawn feed for example.

This Scotts Spring/Summer Lawn Builder (https://www.amazon.co.uk/Scotts-Lawn-Builder-Food-8kg/dp/B002B550OS/) has an NPK value of 22-5-5.

But this grass feed by Elixir Garden Supplies (https://www.amazon.co.uk/Elixir-Gardens-Fertiliser-Control-Magnesium/dp/B00CBUE3XW/) has an NPK value of 12-3-9.

Can anyone explain why they vary so wildly?

wild edges

It doesn't vary that much. The 12-3-9 is equivalent to 22-5.9-16.2 so it's only the potash level that varies and I assume that's just their formula to strengthen the grass against stress. The higher number mix is a slow release type so it's probably more concentrated to work over a longer period.

b3n.doyle

wild edges said:

It doesn't vary that much. The 12-3-9 is equivalent to 22-5.9-16.2 so it's only the potash level that varies and I assume that's just their formula to strengthen the grass against stress. The higher number mix is a slow release type so it's probably more concentrated to work over a longer period.

Thanks for that. 

But how did you come up the the equivalent numbers?

thanks again.

glasgowdan

The 12%N product is actually equivalent to 30% of the other one, given it's described as a 10-week feed as opposed to 4-week. 

Both are fairly high however, and likely to result in a high level of thatch build up during the season.

Fertilisers on the domestic market are very basic and the numbers don't bear any relation to what your lawn actually needs for proper healthy growth.

b3n.doyle

glasgowdan said:

The 12%N product is actually equivalent to 30% of the other one, given it's described as a 10-week feed as opposed to 4-week. 

Both are fairly high however, and likely to result in a high level of thatch build up during the season.

Fertilisers on the domestic market are very basic and the numbers don't bear any relation to what your lawn actually needs for proper healthy growth.

Thanks, I appreciate your answer

I know many domestic products (such as the ones I mentioned in my original post) contain way too much nitrogen and manufacturers use it to stimulate quick growth to keep their not so well informed customers happy.

I'm also aware that this surge in growth can cause excessive thatch.

So with that said, what NPK values would you look for when buying a spring/summer or autumn/winter lawn feed?

Thanks again.

glasgowdan

I use different levels of the key nutrients depending on a few things; the current grass growth, the customer's mowing habits/availability, how much use the lawn gets etc. 

I can't really give numbers, but if it's your own lawn, little and often is better. Half-dose the feeds every month if you can. Use a little iron once in the spring/summer period to knock back any moss, scarify lightly, use a roller mower for a smoother surface.