As flood water covers grass and plants it enters spaces between the soil where oxygen is stored. As the water enters these spaces in the soil the oxygen escapes so there is none available for the microbes in the soil, or the plant roots to encourage growth. This in essence drowns the plants.
Before you begin clearing up after the flooding take a few some photos of the damage the flooding has caused. Some insurance companies may request this as proof of damage, and some may even cover the cost of replacing any damaged plants.
Recovering your lawn
Your grass can usually last up to a week underwater without too much trouble however this varies on a case by case basis. Your first job after the water has drained away is to remove any debris. It is recommended that you wear a pair of gloves and waterproof clothing to do this and start with the larger objects first.
Try and avoid walking on your lawn if possible, to prevent the soil from compacting. Compacted soil stops oxygen from reaching the roots of the grass which is required for growth. Walking on the lawn may also tear up the grass and create a muddy mess where your grass once was. If you have to walk across your lawn, try and spread your weight as much as possible by walking on wooden boards.
If the rain or flood water has left a layer of silt on your lawn 20mm thick or greater, you need to remove this as soon as possible using a flat spade and running water. If your lawn was flooded with salt water you need to use the same process as if it is covered in silt. The sodium in salt will crystallise on top of the lawn and prevent oxygen and sunlight reaching the soil.
When the grass is debris, silt and salt free use a garden fork and spike the ground to a depth of around 10mm to allow air to get to the roots and aid further drainage.
Once the grass is clear you then need to think about replacing any nutrients the grass may have lost. Large amounts of water can wash away the nutrients in the soil which are needed by the grass to grow. If the lawn has been submerged for a few days it is a good idea, to add a heavy nitrogen filled fertiliser to the lawn to encourage the grass to grow.
Note: if you lawn was flooded with salt water do not add fertiliser. Many fertilisers include sodium which is found in salt water. Too much sodium is a bad thing for your grass and may cause more harm than good.
Remember never to mow the lawn when it is wet whatever state it is in. This is likely to damage your grass and to damage your lawnmower as well.
Saving plants from flooding
Unlike your grass your plants are likely to be the real victims of flooding. They will begin to wilt and die within a couple of days. Obvious signs that your plants are drowning include them turning yellow or brown and the leaves curling. Unfortunately there is not a great deal you can do for them if the water is still around, however once the water has drained away you can go to work to save them.
Once the water has resided, begin by gently removing any mud or silt from the leaves of the plant. Remember to wash both sides of the leaves with running water. This will ensure sunlight can be absorbed by the leaf which is required for them to grow.
Once the soil is beginning to dry out around the plants, turn the soil. This will add air into the soil aiding the growth of the plants and help dry the soil out further. Trim off any branches or flowers that look like they are dead or dying with a pair of sharp secateurs – Gardena’s are highly recommended. This will allow the plant to focus on saving the rest of the plant rather than the part that is dying. It is also recommended that you take some cuttings of any plants you like. This is recommended as it maybe weeks later before the plant dies due to the flooding.
Finally add a nitrogen rich fertiliser to the plants to give them a kick start and encourage growth if they were flooded with fresh water.
Fences and buildings
After a flood you will need to wash down any greenhouses, fences and brickwork. It is advisable to use hot soapy water where possible. Brickwork and fences will eventually dry out however it may take some time. When dry, you should re-point the brickwork to make sure it’s watertight once again, and paint fences with weather-proof paint.