Ecologist, kitchen gardener and garden writer Becky Searle explains how to deal with floodwater in your garden or allotment...
Winter is a magical time of year. The garden is regularly painted with sparkling frosts, and the triumphs and woes of the seasons passed are erased as the blank canvas of a new season is presented. But winter can also bring some uniquely difficult challenges with increased rainfall, strong winds and snow.
Flooding can be utterly devastating and unpredictable, and worse still, it can happen regularly.
Most plants can cope with being waterlogged for short periods, but to cope with prolonged root submersion, plants need to have special adaptations. If they don’t possess these adaptations, waterlogging can kill plants quite quickly.
The reason for this is that plants’ roots need to respire. They take in oxygen and release carbon dioxide like you and me. Luckily for us, plants photosynthesise and do the opposite in much more significant amounts.
So, what can we do if our garden or allotment gets flooded or waterlogged this winter?
Dealing with Standing Water
It can be heartbreaking to see your garden or allotment underwater. Unfortunately, whilst the water is there, there is very little we can do about it. Floodwaters can be dangerous, too. Firstly, we can’t see where we are putting our feet, so just walking around could be hazardous. Flood water can also contain contaminants, so take precautions. It's worth waiting until the water subsides before entering your garden or allotment.
If the flooding is minor and the ground is wet but not underwater, going around with a fork and putting some holes in the ground (not digging, just piercing the surface) can help the water drain away and maintain the air in the soil whilst it dries out.
If your growing space has been flooded once, there is a good chance it could be flooded again, so let’s look at some ways to prevent it from happening.
Problems with Flooding
Aside from the obvious problems regarding access, flood waters can cause some problems with your soil. As water drains away, it takes with it water-soluble nutrients and minerals. This is called leaching, and it can leave the soil slightly more acidic. Doing a pH test and adding some lime might be necessary, particularly if the flooding is severe or regular. Don’t add lime unless you are certain that the soil needs it.
Prevention is better than cure
Some sites are a lot more prone to flooding than others. If your garden or allotment is prone to flooding, you will want to take some preventative measures. The quickest and easiest way to do this is to create raised beds. By creating raised beds, you raise the level that water would need to get to start becoming a problem. Let’s look at some other ways to deal with flooding on your allotment or in your garden.
My answer to almost everything involves plants. If there is a question, nature usually has the answer! So, my first port of call when you have a site prone to waterlogging is to include some strategic planting. Quite often, flooding occurs just in parts of your garden or allotment. If an area is particularly prone to flooding, plant something that enjoys lots of water or doesn’t mind poor drainage.
On my new allotment, there is a part where water drains off the slope and pools next to the shed. It’s pretty well-drained, just very wet! So, I’ve decided this is the perfect place to plant my rhubarb and asparagus, as they both enjoy moist soils. So be creative with what you are planting where.
Some plants can also help to break up the soil and improve drainage. Alfalfa is a good example that is easy to grow. It is also in the legume family, so it will help replenish nitrogen in the soil.
Banks and Ditches
Banks and ditches can be helpful tools against flooding, where the flooding occurs due to an overflowing water source such as a pond, river, or stream. Similarly, you can use ditches to drain off water that comes in from a specific direction, like water flowing downhill. Use banks as a physical barrier where appropriate, and plant into them to give them extra structure.
Creating drainage is essential when it comes to preventing flooding. If the soil is not naturally free-draining, it could be because it is overly compacted soil. In this case, decompacting the soil with plants or, in extreme cases, with a fork, putting holes into the ground might be necessary to introduce some air flow to the soil before anything else.
Soakaways, sustainable urban drainage systems, natural ponds, and French drains are all valuable tools. Choose the one that best suits your space and adapt it to meet your needs. There are many excellent resources about this, and I recommend starting with sustainable urban drainage systems.
Improving the Soil
Healthy soil is usually naturally well-drained. By improving the soil, the organisms that live in the soil will improve the drainage for you. However, if the area has been routinely underwater, or the soil is compacted from heavy machinery or the like, it must be aerated first. If there is no oxygen in the soil, there won't be any earthworms, arthropods, or good bacteria that we need to create a healthy soil environment.
Most soils are lacking in organic matter. This is because organic matter breaks down over time and with repeated digging and ploughing. Organic matter is all carbon-based. Once this is fully broken down, the carbon in the soil can become oxidised and return to the atmosphere as carbon dioxide.
Adding lots of organic matter will help the soil improve its drainage on its own. It will also build soil health, which will help with nutrient availability for your plants. Going no dig will also improve the drainage in your soil. You will find that regular digging has the opposite effect and leads to compaction. Steph Hafferty wrote a brilliant article for Dalefoot about applying no dig gardening, which is well worth a read.
Building Raised Beds
We have touched on this already, but raising your beds will make it easier to create healthy, well-drained soil, at least in the top 6 inches where the majority of plant roots are. This reduces the chances of our plants’ roots sitting in water for long periods.
Once floodwaters retreat and the ground is workable again, consider adding some preventative measures to try and stop it from happening again. It is also critical to improve the soil at this point. You might want to do a soil pH test. If it is particularly acidic, consider adding some lime. The bacteria and fungi in the soil may help clear any minor contaminants, but if you are worried, it's worth talking to your local environmental health team. They may be able to test the soil and at least put your mind at ease.
Using a good quality mulch such as Lakeland Gold will help add structure to your soil and improve drainage. It will also feed the life in the soil, helping release nutrients. The best time to do this is when the beds are empty. Usually, this is in autumn, winter or spring. Mulching in autumn can help protect your soils during winter. I recommend applying a mulch annually so that your soil improves year after year.
Becky Searle is an Ecologist, Garden Writer and public speaker specialising in soil health and vegetable growing. Visit Becky’s website at www.sowmuchmore.co.uk or follow her on social media under Sow Much More.