Many lawns will be able to handle a few days of flooding with not too many problems. Major flooding, long periods of flooding or flooding numerous times over a short period of time, may require some extra special attention to get your lawn back on track.
Allow flood waters to drain away naturally. While still wet, limit the traffic on the lawn so as to avoid soil compaction. Avoid mowing until it is dry enough that the mower will not cause even more damage.
Even if your grass has grown quite long and quite quickly, resist the temptation to cut the lawn too short. Never mow more than one third of the grass plants at any one time. Plan to mow more frequently in the weeks after flooding, rather than damaging the plants by taking too much off at once. Limiting the mowing will also give you the advantage of being able to easily see any weeds in the lawn, as they will grow faster and higher than the lawn.
Once the water has drained away, remove any debris such as branches, leaves and palm fronds. Any organic matter left on the lawn will start to decay causing problems for the lawn plants and will encourage the growth of fungi such as lawn mushrooms.
If up to 20mm of soil or silt is left on the lawn it can simply be spread evenly over the lawn with a rake, like an application of top dressing. More than 20mm of soil or silt can cause issues, so you will need to carefully remove the excess, limiting any damage to the grass plants below and then spread the remaining 20mm over the lawn. In both cases ensure that the tops of the grass plants are visible through the soil, when you have finished spreading the soil and silt.
In the South East Queensland warmer months it is recommended that you apply fertiliser after the flood waters have receded, to help the lawn bounce back by replacing any nutrients that may have been washed away.
It is also advised that you aerate any compacted soil so that nutrients, water and oxygen can move through the soil more easily. Undertaking this process while the soil is still slightly moist should be possible with just a garden fork. Insert the fork at evenly spaced intervals to create pockets in the lawn.
We know how stressful flooding can be to us and our lawns are no different. The stress caused by flooding will make your lawn much more susceptible to disease, pests and weeds. Keep a close eye on your lawn while it recovers and deal with any issues as they appear and before they take hold. Trim overhanging branches to allow more sunlight to reach the lawn to dry out excess moisture and limit shaded areas. Remove or treat fungi and weeds as they appear. Treat any pest infestation sooner rather than later. Giving your lawn a bit of extra help while it is recovering will give it a much better chance to regain optimum health and fight off any pest invasions.
If you have suffered from a major flood, prolonged flooding and very fast moving floods, installing a new lawn may be the best option. Some floods can cause such extensive damage that even the most hardy varieties of lawn will struggle to repair and recover.