Lawn Burn

No Scorch Fertiliser

What is Grass Burn or Scorch?

You may have experienced or heard of fertiliser burn or scorch on the grass. The term is descriptive rather than scientific. Green or organic fertilisers, composts, mulches or manures are not considered to have scorch risk whereas manufactured, mineral or non-organic fertilisers can have varying degrees of scorch risk and those are the ones we consider here.

Burn Type 1: Fertiliser, being a salt, and if of a powdery nature, will, if left in contact with the grass leaf, absorb moisture from it. This dries the leaf causing it to shrivel and therefore look like it’s been burned and sometimes will turn black

Burn Type 2:  Fertiliser if over applied in good moisture conditions (typical of hand spreading) or if applied at the correct rate when moisture levels are too low have the potential to burn. The changing climate is causing long periods of dry weather, particularly in spring which increases all burn potential from fertiliser. Lawn care companies in particular have a hard time with this problem.

By over applying or applying when moisture levels are low causes a high strength fertiliser solution to develop in the soil and by osmosis ‘sucks’ moisture out of the grass plant causing a brown straw like burn. It is therefore advisable to check for sufficient soil moisture before applying fertiliser; the fact that it rained earlier in the week means nothing! It is always preferable to apply Lawnsmith fertiliser after rain rather than before just in case the forecast rain doesn't materialise.

Why does Burn Occur in Patches?

To burn the whole lawn you would need to over apply by quite a lot, very evenly and in low moisture conditions. This would be extremely rare. The most common cause of burn is uneven spreading by hand or a faulty spreader. This means too much is applied in some areas only hence a patchwork effect of brown or black patches.

High Grass Scorch Risk

This effect is increased when using combined grass ‘weed and feed’ fertilisers. By their nature they are a very fine granular or powder product to enable good contact of weed killer and weed leaf. This fine quality increases the contact area with the grass leaves therefore increasing scorch potential. Secondly if the lawn fertiliser is ‘quick release’ then it is all ‘active’ and has even more burn potential.

In addition, any fertiliser containing iron (ferrous sulphate) will also have a greater burn risk e.g. 4 in 1. This is not to say iron is a bad thing but when combined with other salts the total package is more aggressive.

Minimal Grass Scorch Risk

On the other hand the salts in controlled or slow release fertilisers are ‘locked up’ to a certain degree thus limiting the dangers. Secondly, fertilisers such as Lawnsmith® Fertilisers are granules or pellets that will bounce or roll off the leaf into the soil thus minimising the amount of fertiliser contacting the grass leaf. This considerably reduces burn or scorch potential.

No Scorch Fertiliser

This is usually 100% coated and requires moisture to break down the coating and release the contents. These are normally used by lawn care companies because they need to safely feed lawns according to a schedule NOT according to the lawns requirements. This means they may need to feed your lawn during a hot dry spell otherwise they won't earn their fee. You, on the other hand, live close to your lawn and can feed it during the right conditions just like the greenkeeper or groundsman does to the turf he/she cares for.

The problem with feeding in very low moisture conditions (as lawn care companies do) is that though the feed doesn't burn at the time of application it does remain ready to be activated when conditions improve. If conditions remain dry and they return for another treatment you now have a double dose. If you now get a little rain it will activate and you now have a lot of fertiliser in the ground and not enough water. You now have burn type 2!

Liquid Fertiliser

This refers to fertliser products in liquid or soluble form applied by sprayer or watering can.

Many people wrongly assume that because these are applied in water they have considerably less scorch risk than dry products. If applied in good moisture conditions at the correct rate they are very safe but, if the grass is struggling for moisture the application on the leaf of a salty fertiliser solution may cause instant burn which can be made worse by dry winds and direct sunlight. This applies to all liquid fertilisers including Lawnsmith Soluble Fertiliser and also Green-up Ferrous Sulphate at low to medium rates. However, it is normal and to be expected that Ferrous Sulphate applied at rates to affect moss always runs the risk of some slight temporary leaf burn.

The Compaction Effect

Old lawns (20years plus), those with high activity (play lawns) and areas of high traffic (paths to sheds or clothes lines) become compacted over time. The compaction reduces the capacity of the soil to hold air and water thus increasing the risk of fertiliser burn even in good conditions. Regular aeration reverses this effect and increases the life span of your lawn.

There was Plenty of Water

'I watered the lawn beforehand', 'it rained' or 'I watered it in' but it still burnt my lawn are the typical comments we hear. This is just a miscalculation as the output from a sprinkler is not very high and rain can be light, heavy, prolonged or a shower. Add into the equation any compaction means that any two lawns can respond to watering quite differently. This means that judging the amount of water in the lawn based on a sprinkler or rain is not going to be accurate so you need to actually check the soil.

Lawn Moisture Test

You could dig down into the lawn a few inches and check for moisture but a crude but often accurate measure of soil moisture for lawns other than those on very sandy soil is to use a 6" phillips screw driver. If it pushes all the way into the lawn easily then you have a very moist lawn. As the lawn dries it will get harder and therefore the screw driver will not penetrate as far. If the driver won't go in more than an inch or so then your lawn is starting to become dry and care should be taken. Any less than an inch of penetration and I'd classify the lawn as dry and therefore refrain from treatments.

In summary

All fertiliser, other than 100% coated or 100% organic, has scorch potential with some doing it more readily than others. At Lawnsmith we have taken great care to balance our products so that the scorch risk is minimal as long as you apply when there is reasonable ground or soil moisture. If there is no moisture why waste your money fertilising - it won't do any good until the soil regains moisture!

What to do if you have Burnt the Lawn

You can’t remove the fertiliser as it’s already started to react and burn. The best thing to do is dilute it with water and stimulate growth so that the scorched leaves grow out. This means turning the sprinkler on and watering for several hours a day for several days depending on how much damage has been caused. The best time to water is straight after fertilising if you think you’ve over done it or when you first notice the damage and then continue with morning only watering.

The degree of burn may vary so fast action always helps. A leaf burn is just that, and the plant is fine and will recover over a few weeks. A crown burn means the damage is severe and has destroyed the grass plant. Unfortunately it is hard to differentiate until the lawn starts to recover or not as the case may be. This may take several weeks and if it doesn't recover then you will need to re-seed the area.

Warning: If you use too little water you can dissolve more fertiliser which then doesn’t get diluted sufficiently which then burns new areas. When watering you must drench the lawn, area by area.

Getting it right next time

For the future assume the error is in too wide an opening, walking too slowly and possibly too much overlap. Next time you feed, weigh out the required amount and only put that amount in the spreader. Set the spreader to the lowest setting advised and don’t overlap. Once you’ve done the lawn you should have enough left to do a second dose which would be the overlap. Practice with uncooked rice if you wish.