The effects of frost on lawn
Author: Stefan Palm Date Posted: 8 July 2016
When Autumn turns into winter, it is common for some varieties of lawn to begin to lose 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.
Why is this so, I hear you ask. Well, for all the plant geeks out there (you know who you are ) there are very interesting reasons for this, which at the risk of sounding to techy, I’d like to explain to you.
Cool seasons grasses like rye grass and tall fescue have a sensational ability to stay green in winter, even under the coldest of South Australian conditions. They are commonly referred to as frost tolerant and 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 during the cooler months meaning these are the times they are looking their best. Along with this, they have a natural defence against frost. Cool season grasses such as Rye 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 brown lawn, it just means its 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 its cell walls which is why it looses its 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 during winter.
The good news is simple frost can’t kill your lawn. It can only discolour it so in that sense its just a cosmetic effect. As soon as winter turns to spring, your lawn will awake from its winter 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.