Edition 30: How to look after warm season grass in the cooler months

In this edition, we are going to look at how to keep a hold of our warm season (C4) grasses during the cooler months. This is assuming you haven't oversown the lawn with a cool season variety for the cold months.

 

The first thing we need to address is dormancy. Contrary to what some may think, the grass isn’t dead during winter—it’s simply dormant, much like a form of hibernation. This natural pause in growth is triggered by two key factors: soil temperature and light.

Warm-season grasses generally begin to enter dormancy when soil temperatures drop to around 13–17˚C depending on the variety and its “normal” temperatures.  Adding to this, reduced light intensity and shorter daylight periods also play a major role. While light availability is a year-round consideration, it becomes especially critical in winter. C4 grasses, in particular, still require a minimum amount of light to help reduce the level and duration of dormancy.  After all its sunlight in the lawns canopy that provides warmth.

The amount of light needed depends heavily on the intensity/quality and consistency of sunlight. In full sun, as little as 1.5 hours per day may be enough, but in heavily shaded areas, it could take up to 11 hours. That said, it’s important to note that light alone isn’t enough to prevent dormancy—it can only help narrow the window in which it occurs.

However, like most things in turf there are some things we are able to do to hopefully shorten the time our C4 grasses are dormant, or in some cases, avoid it all together. 

The first line of defence is fertilisation, the first step in the fertilisation process has hopefully already happened. That is a late autumn granular fertiliser with additional potassium to help strengthen the plant. (See edition 29) 

The next is reducing the amount of Nitrogen, yes some is acceptable, pre dormancy, to hopefully help the grass “tick along” rather than push too much growth this time of year increasing the risk of disease. Combining this with a quality plant available source of Iron, to help darken the grass to absorb more light producing warmth. The “autumn” balanced fertiliser can look very different to a balanced used in spring and summer, but will still have the required levels of N-P-K and trace elements essential for this time of year. 

Why not go further and support the plant with the essential hormone and growth stimulant compounds the plant struggles to produce in these conditions.  Particular products and bundles of the Lawn Addicts Fertech range are the market leaders for these situations, carefully formulated offering a holistic approach to plant health during these months.  All contributing to lessening the effects and shortening the dormancy window.

 

The last, and potentially most controversial, to some people, is Pigment. Yes, pigment on pre-dormant warm season grasses can help minimise dormancy and improve winter colouring. However, these are more than just a paint or colourant for turf. They can actually help the grass absorb more light and heat required for photosynthesis (between 400-800nm) and can also act as an insulator to help the grass stave off harmful UV rays which contribute to the health of the leaf when plan regeneration is slow.