A garden or allotment can look a complete mess after surging floodwaters have passed through. It wouldn’t be so bad if it was just rainwater, but most flood water carries with it all sorts of contaminants – plastic, sewage, manure, slurry and chemicals, such as oil and pesticides, and much more besides. So, if you suspect that the water is contaminated, wear protective clothing and waterproof boots while in the garden and keep pets away.
It best to avoid going into the garden until the flood waters have drained away. Before you do so, make sure the electricity supplying any outside sockets is turned off and don’t turn it back on until everything has been checked. All the rubbish from a flooded garden is classed as controlled waste as it may be contaminated, so it must be thrown away in skips provided by the local council.
Although it may be tempting to keep sandbags for another time, they should be thrown away as they will also be contaminated. The same is true for any bags of compost, sand from play areas, bark chippings and so on that came into contact with flood water.
Water can do a surprising amount of damage to the foundations of buildings and retaining walls, so check for damage. Unblock drains and hose down hard surfaces such as patios, paths and walls. Then check for any cracks or other signs of damage. Don’t forget that wooden arches and pergolas may be damaged at ground level.
The soil is going to be waterlogged for some time and, when it is in this state, it’s easily damaged and susceptible to compaction, so don’t walk on it and cause further damage. If you need to gain access or cross a flower bed, use a scaffold board to spread your weight. Lawns, too, will be waterlogged and vulnerable to damage.
Can I eat my veg?
Short answer is no. Never, ever, eat any vegetables that were in the ground at the time of flooding, even those that will be cooked. Guidance suggests that the ground should not used for at least ONE year and even LONGER for salad crops, to sure that sure any contaminants, spores, and disease-causing bacteria are long gone.
If your vegetable plot has been flooded and you have lost your crop, the quickest way to recover is to build some new raised beds and fill them with bought-in compost so that you can use the growing space. The ultimate ‘quick fix’ raised bed is a one tonne bulk bag filled with compost. You can make use of containers and grow bags too. But, don’t be tempted to fill the new beds with compost from any compost bins that have been flooded.
After the flood
If it’s a flash flood, it’s unlikely that long-term damage will have been done, but heavy rain or flood water pouring in from rivers may result in standing water in your garden for days, or even weeks. The excess water drains slowly into the soil creating waterlogged conditions. Waterlogging stresses plants. The water fills the air spaces in the soil, pushing out the air and creating anaerobic conditions around the roots, which can cause them to die. Few species can cope with waterlogged roots for long, apart from those adapted to living in boggy areas, such as willow.
In the weeks following a flood, look for signs that flooding has damaged your plants; you may notice stunted growth, yellowing of leaves and leaf drop. Leaves wilt because the roots are dying and starting to rot. If you dig up the plant, you will probably see blackened roots and they may smell or have rotted away already. The dying roots mean there is no transpiration stream, so water and nutrients are not moved around the plant and the leaves wilt. It seems odd that the plant is water stressed when its surrounded by water, but it has no means of taking up the water. You may also notice that bark starts to peel on shrubs and trees, and growth in spring is slow or stunted and some branches start to die back. Prolonged waterlogging may result in the decay of the root systems of herbaceous plants, so they don’t reappear in spring and bulbs may simply rot in the ground.
What to do?
Firstly, cut away any dead stems and branches, and prune the plant into shape. Once you see some new growth, give the plant an organic feed. Any valuable plant can be gently removed from the ground, its roots washed and the plant can then be replanted in a drier part of the garden or a large pot. If you have a lot of plants to rescue, but you still have a waterlogged garden, find the driest area, dig a trench and backfill it with a free-draining mix of soil, grit and compost and use it as a nursery bed while you sort the rest of the garden out. For plants that are too large to move, dig a shallow trench around them to help the water drain away from their crown. Forking the ground around shrubs and trees helps to boost drainage too.
Flood waters may have carried away some of the soil’s nutrients, especially soluble nitrogen, so to repair the damage, mulch your beds with a good compost to boost nutrient and organic matter levels and, if necessary, feed the plants in spring. A long-term slow release organic feed can help trees and shrubs. Damp conditions can persist for some time, so expect more slugs and snails and fungal disease. Eventually, once the soil is dry you can start remedial action to get rid of any compaction, for example by forking and loosening the soil.
If there is little you can do to avoid flooding, aim to grow plants that can cope with floods and waterlogged soil (see our list in the appendix). If you have vegetable beds, avoid growing crops over winter. Instead, focus on planting out in spring and harvest them by late autumn to avoid the wettest months of the year. During the rest of the year, keep the soil covered to protect it and prevent weeds growing, either with a layer of compost, black plastic, or mulch. And in the long term, look at some of the slow water options describe later in this chapter and in chapter 7, such as building raised beds so that the water runs between the beds, keeping the root zone above the water. Lawns don’t thrive with regular flooding and waterlogging, so it may be best to replace a lawn with gravel or decking or you might even plant a bog garden with a raised boardwalk to provide interest and a different vantage point.
This is an extract from The Climate Change Garden written by Sally Morgan and Kim Stoddart. To buy the book visit www.climatechangegarden.uk