Fertiliser burn in lawn

As most home gardeners will attest to, there are times when your lawn appears to burn and go brown after the application of fertiliser – which of course, is the complete opposite of what you would expect. So how does this happen, and how can you avoid it?

Fertiliser burn occurs primarily due to poor application methods. Yep – it’s almost always user error, I’m afraid. While it can happen with organic fertilisers, it mostly occurs with the granular chemical type.

Why does it happen?

When you apply fertiliser, it is critical that all of the fertiliser that you apply is thoroughly watered in so that you can’t see it on the surface.  Fertiliser burn occurs when too much fertiliser is left on the surface for an extended period of time. The only exception here is for the slow release type fertilisers where it is OK to leave some fertiliser on the surface.

Chemical fertilisers are made up of mineral salts. These salts come in the form of nitrogen, potassium, phosphorous and all the other trace elements essential to lawn growth. After application, they need to be watered into the soil so that the lawn roots can take them up.

If you over-apply mineral fertilisers, apply them unevenly, or apply them to a wet lawn, they can have the unintended effect of drying the lawn blades out. Suppose the fertiliser granules come into contact with the lawn blades for an extended amount of time without being watered in properly (eg overnight). In that case, the mineral salts in the fertiliser will begin to draw the moisture out of the blades, which causes them to go brown. The longer the fertiliser stays on the surface of the lawn, the worse the problem will become. Essentially, it’s the effect of too much fertiliser staying on the surface of the lawn for too long.

There are a few common mistakes people make. The first is applying the fertiliser by hand instead of using a spreader. This can lead to some areas getting more fertiliser than others, and it can also lead to instances where you leave piles of fertiliser on your lawn – e.g. fertiliser accidentally spills from the bag as you walk over your lawn, or as you broadcast it out by hand, you don’t do it evenly, again leaving concentrated piles. The other is relying on rain to water in the fertiliser. While it sounds like a good idea (and often is), the fertiliser won’t get watered in properly if you don’t get enough rain.

How can you tell if this is the reason for your patchy lawn?

It’s easy to mistake fertiliser burn for other issues such as disease or insect damage. If you find that your lawn has gone a patchy brown colour the day after you fertilised, go out and take a closer look at one of the brown patches. If you can peel apart the thatch of the lawn and see fertiliser still on the surface, you can confirm it’s probably been burnt.

Will it kill your lawn?

It depends on the type of lawn you have and how long the fertiliser stays on the surface. If you have a couch, kikuyu or buffalo lawn, it will recover. The warmer it is, the faster this will happen. If you have tall fescue, rye or bluegrass (i.e. a non-spreading variety), fertiliser burn can permanently damage these lawns. In these instances, you may need to oversow burnt areas.  What I can say is that the faster you intervene, the less severe the problem will be.

How do you avoid it?

There are two simple ways you can avoid fertiliser burn. I would recommend applying fertiliser via a spreader rather than by hand. That way, you apply it evenly and avoid touching it too much with your hands. If you do apply by hand, make sure you do it sparingly and evenly. If you have a spill or over-apply, remove or disperse fertiliser in these areas as much as possible.

The second way is to water the fertiliser in thoroughly after application.  Remember that some fertilisers dissolve faster than others, so make sure you inspect the lawn once you’ve finished to see that you’ve watered it all in.

Handy Tip: Take a 2 stage watering approach. It often helps to lightly water in your fertiliser immediately after application. This helps to soften the fertiliser. Come back 10 minutes later and give the lawn a thorough watering. You’ll find it much easier to water in the fertiliser this way.

What can you do if this happens to you?

If you notice your lawn burning after the application of fertiliser, the first thing to do is to apply more water. Get out on your lawn with a pressure nozzle on your hose and blast the fertiliser into the soil in problem areas. This will stop further burning. As I mentioned earlier, most lawns will recover. If you have one of the non-spreading types, give it a few weeks to get a better picture of the damage. At this point, you will know which areas may need to be oversown.

If you’re having problems with fertiliser burn or anything else lawn related, give us a call on 8298 0555 or email me at stefan@paulmunnsinstantlawn.com.au. We’d be happy to help.