Grow veg

Rain, rain go away – the problems with saturated soil

When I originally wrote that this was going to be a warts and all vegetable growing blog I hadn’t thought about the problems of flooding, but that’s what many people are dealing with at the moment. Not that I’m talking about the disastrous floods that have affected houses, businesses and farmland in so many parts of the country, nor am I suggesting that a saturated allotment or vegetable patch is comparable to that, but it’s a fact that the amount of rain we’ve had this winter presents a challenge to a lot of gardeners in the form of unworkable mud and standing water on their beds.

Not the devasation seen in some areas, but mud and puddles everywhere

My garden at home is well drained and apart from an unusual amount of moss (which I rather like) and a lot of mud where there used to be grass (which I don’t like) isn’t suffering too badly. The allotment is another story. The soil at the allotment is heavy, with a dense layer of clay not far below the surface. Like many plot holders I’ve managed to improve the topsoil over the years to a point where it can cope with a certain amount of heavy rain, but the underlying clay means it never drains well and with the sort of rainfall we’ve had this winter it becomes saturated. We are now well beyond field capacity. In fact, the whole site becomes so saturated that you squelch along the wide grass paths as you walk past plots that for the most part are a sea of increasingly large puddles and sucking mud.

Looking over a neighbours sodden allotment plot

It was bad before Christmas, when I found myself making use of large puddles to wash mud off my parsnips and watching my autumn onion sets bobbing around in several inches of water. I was wondering then whether even the kale would give up when I could see that the brassica bed was also under water. The situation improved a bit in January, the kale kept growing, there were still some sprouts, and being able to pick purple sprouting broccoli and pull leeks felt like a real achievement. But then we got into February and the recent run of storms (Ciara, Dennis, Ellen) reduced most plot holders, including me, to paddling again. If anything, the problem at the moment is worse because saturated soil has a tendency to slump as the water recedes, undoing the crumb structure and its associated air pockets which normally help it to drain. This second soaking might take longer than the first to resolve itself and leave me with poorer soil. I haven’t really done anything down there since I pruned the apple tree and now I’m resigned to waiting till things settle down before I can get started.

The puddles were useful for cleaning the worst of the mud from the Christmas parsnips

I’m sure the rain will ease up eventually.

But I’m equally sure that we’re likely to see more of this sort of weather, so what practical steps can we take to help ourselves?

Improve the soil

If you read Charles Dowding’s brilliant blog, you’ll know that his soil has coped well with the rain. He’s mentioned a couple of times that it drains well, and they’ve been able to work on it pretty much as normal. When I was working on the Which? trial garden beds at Capel Manor College in north London, they always drained well, too. Even after heavy rain we only had to wait a couple of hours and then we could go out and work.

The common factor in these two gardens is soil that’s had a lot of organic matter added to it over the years. In the trial garden, we used to mulch the beds every winter with either mushroom compost or green waste manure. We changed tack a few years ago because we were getting too much fertility in the beds for some of our trials, and too many weeds, so we started to use Strulch instead. Strulch is a mineralised straw mulch that takes 18 months to two of years to break down. It suppresses a lot of weeds and helps keep slugs and snails at bay, which is a big bonus. Unlike Charles Dowding we used to rotovate the beds every year or two as trial plants were removed but still, drainage was good because the addition of organic matter improved the structure (both through physical and chemical processes) allowing water to drain through quickly.

Having said that, there was one bed which had a layer of clay under the topsoil and when the rain was heavy and frequent, that bed used to end up with standing water on it, just like the allotment.

Raise the level of the soil

You can raise the level of the soil so you’ve got more depth and so better drainage either by building raised beds that you then fill with a mix of topsoil and compost, or more simply by profiling them. This means taking soil from the bed edges and putting it into the middle to create a higher, but flat, central planting area with slightly sloping sides. It only needs to be slightly above the level of the surrounding paths or grass as that central area can drain into the gutters along the bed edges. It makes it easier to edge the grass on the beds as well.

Adding a layer of organic matter also helps to raise the level, at least temporarily, and it can warm the soil. Plus, it creates a layer that isn’t saturated and, if you time it right, won’t become as wet as the soil underneath, so you might be able to get started with direct sowing or planting a bit sooner.

Add drainage channels

My allotment site is on a hill and quite a few plot holders use gravity to help by digging drainage channels to take water away from their plots. You need to work with neighbours on this – our drainage channel started to create a flood on our neighbours plot and for one reason or another they weren’t able to continue it, so we had to partly divert it and stop it somewhere in between. On another part of the allotment site some more organised people have dug an impressive channel that runs downhill towards the perimeter fence along the back of more than half a dozen plots. At the moment a small stream runs through the channel, disappearing eventually into a pipe that’s been laid under the grass. Although the ground is still wet it takes the worst of the water away very effectively.

Wait – and work in the greenhouse

Patience is the only other option. Clay soil not only gets wet it gets cold and the combination will never grow good plants. Even if your soil isn’t as heavy as mine, if its wet and still cold seeds won’t germinate and roots are more likely to rot than grow. I’m lucky that I have a small greenhouse in my back garden and I would normally get things under way in pots and trays in there, and on the kitchen windowsill. When we finally get some sun and dry weather and the soil hits that brief, sweet spot between unworkably wet and so dry it sets hard, I should have plants that are well on the way to being ready to go in. There will be plenty of time to catch up then.

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