The effects of frost on lawn

Author: Stefan Palm   Date Posted: 25 June 2019 

With the first severe frost event of the season occurring on Monday morning, much of Adelaide's lawns were covered in a thick layer of ice. Unfortunately, frosts like these will almost certainly result in immediate colour loss.

Why is this so, I hear you ask. Well, for all the plant geeks out there, there are some very interesting reasons for this. 

When Autumn turns into Winter, it is common for some varieties of lawn to begin losing their colour. Colour loss can range from slight discolouration right through to a total browning. The reason for this is all related to the cold temperatures of winter. The colder it is, the worse it can be. Frost is a major contributor to lawn discolouration, as anyone living in the frosty parts of South Australia will attest to. Frost is the freezing of dew which typically happens in the early hours of the morning. As the dew freezes, it has the potential to freeze the lawn’s blades, leading to discolouration.

Some lawns are effected more than others. Generally speaking, there are 2 categories of lawns in Australia. Cool seasons grasses like tall fescue and rye grass and warm season grasses which include couch, kikuyu and buffalo. The warm season grasses are the most common types in South Australia and also the most likely to succumb to colour loss during winter.

Cool seasons grasses like rye grass and tall fescue have a sensational ability to stay green in winter, even under the coldest of conditions. They are commonly referred to as frost tolerant or Winter hardy. Cool season grasses naturally germinate and grow in much cooler temperatures than warm season grasses. Autumn, Winter and Spring are their prime growing times as they enjoy the cooler temperatures theses months bring. Put simply, these grasses are in season and looking their best during the cooler months. Along with this, they have a natural defence against frost. They contain what is called IRI proteins. IRI stands for Ice re-crystallisation inhibition. It’s almost like an antifreeze protein that stops the leaf from freezing when exposed to frost. This enables them to hold onto their colour.

Warm season grasses, as the name suggests prefer the warmer times of the year. When the weather consistently dips down below the mid teens, they slow down and go in to dormancy. Dormancy doesn’t mean a brown lawn, it simply means the lawn has stopped growing. The degree to which it discolours will depend on a few things but the major player is how cold it gets. Warm season grasses do not contain IRI proteins which means they will freeze if it gets cold enough and of course when you freeze a plant, you damage it's cell walls which is why it looses it's colour. The other interesting thing about warm season grasses is that many of them contain anthocyanins. Anthocyanins are purple coloured pigments which become more prominent when the lawn is in dormancy. This is particularly evident in some couches and buffaloes during the Winter. In some instances, you can actually see the runners and blades turn a deep purple.

The good news is that frost won't kill your lawn. It can only discolour it so in that sense it's just a cosmetic effect. As soon as Winter turns to Spring, your lawn will awake from it's dormancy and begin to grow again, re-growing the blades that have been burnt so don’t worry too much if your lawn takes a colour hit this Winter. There are a few things you can do to reduce the overall effects including fertilising during Autumn with a high potassium mineral fertiliser such as Emerald Green. Fertilising won’t stop discolouration all together but it will make the lawn more cold tolerant.


Comments (2)

winter lawns

By: on 28 June 2019
I agree my Kikuyu lawn looks pretty awful after frosts here in West Lakes Shore, never known a frost here before. However the Galahs are eagerly eating various critters in it. I do know tho that it will recover, and if it the weather is really dry for a week or so I put on the watering system. Roll on spring!

Mix lawn types

By: on 20 July 2018
Is the conclusion from this article on lawn suggest that if unhappy with the look of your lawn in winter you should mix two types in the lawn area- say Kiku for summer growth and fescue or rye for winter growth? What do they use in football stadiums?

Paul Munns Instant Lawn Response
Hey Mark, The point of the article is to say that warm season grass like couch, kikuyu or buffalo can brown off when they are subjected to frost in winter. This is just a cosmetic effect but can make your lawn look really average. A solution can be to oversow with Rye or Fescue during winter which stays green no matter how much frost it gets. Stadiums like Adelaide Oval have a Santa Ana base but they oversow heavily with turf type fine leaf rye.

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