The Secret to Improving Sandy Soil

Gardeners coping with sandy soil daydream about sticky clay! Light, free-draining, quick to warm up in spring...sounds like horticultural heaven, doesn’t it? But those of us who have actually had to work with sandy soil know better. Sand undoubtedly has its plus points, but it has its challenges, too.

Fortunately, there is a simple way to alleviate some of the problems it presents – namely, poor fertility and a tendency to dry out fast.

How to Tell if You Have Sandy Soil

To work out what kind of soil you have you need to perform a soil test. It’s incredibly complicated and difficult to do, requires much training and effort, and is not for the faint-hearted. Are you game? Okay then, here’s what you have to do:

Take a handful of soil, dampen it, then try rolling it into a sausage shape. Sandy soil will crumble and fall apart. You’ll be able to make out the individual grains. Clay soil will stick together easily and can be rubbed to a dull sheen. Silty soils, which are rare, are often described as having a ‘soapy’ texture. (I don’t know. I’ve never seen it. They’re pretty rare!) Loam – a gardener’s nirvana – is somewhere in between.

And...well, that’s it. Have a cup of tea and put your feet up. You deserve it.

Turn Sandy Soil into Sandy Loam

Okay, so it’s not very scientific, but the test I’ve just described is good enough for most gardeners. If you want more detail, try the Jar Test.

The next step requires a little more work. Sandy soils are less fertile than other soil types, and more prone to drying out, because they’re made up of relatively large particles. This means there are cavernous gaps between the particles, making it easy for water (and water-soluble nutrients) to filter down through the soil, out of the reach of plant roots. We need to partially plug up those gaps and help the soil to hold on to water and nutrients.

So here’s how to do it:

Add organic matter.

It really is that simple!

Organic matter is a kind of cure-all in the garden. You can’t go wrong with organic matter. It will improve any soil type. Any organic matter will work to build soil structure and its ability to hold onto water. Compost and manure are preferred because they are rich in nutrients, which they drip-feed to your plants. Over time, they’ll also help to increase the pH of acidic sandy soils.

I won’t lie – sandy soils do need a lot of organic matter, frequently applied, to make a difference. The warmer your climate, the faster organic matter will break down, and the more often your soil will need replenishing. Start with at least two bucketfuls of organic matter per square metre each autumn, added to the soil surface as a mulch where it will help to protect the soil from scouring rain and winds.

Keep notes on how well your crops fare (our free Garden Journal can help with this) and, if you feel they’re underperforming, up the frequency to twice a year. You could also try three bucketsful, or four. It’s worth adding more in summer if you can too. Grass clippings are a free, regularly available resource that help to reduce evaporation, and they’ll provide a modest flush of nitrogen to boost plant growth too.

After adding all that organic matter you really will need a sit-down and a cup of tea. What the hell – make it a beer!

Best Vegetables for Sandy Soil

Improving your soil takes several seasons. But even with the best will in the world, it will always be sandy soil at heart. ‘Work with what you’ve got’ is good advice! So let’s take a look at which vegetables naturally grow well in sandy soil.

Root vegetables are sandy soil superstars. Motivated by thirst, plants with long taproots like carrots and parsnips are perfectly designed to reach down into the moister soil that lies several inches below the surface.

When you’re itching to get growing at the start of the year, sandy soil is a plus. Warming up and drying out quickly, you’re more likely to have success with early sowings of vegetables such as lettuce and collards.

Potatoes tend not to develop scab in acidic sandy soils, but they are thirsty plants. Less water, more often is a good rule of thumb. This advice doesn’t just apply to potatoes, but all vegetables grown on this type of soil. The same goes for fertiliser. You might want to consider installing irrigation to gradually water and feed your plants.

Mediterranean herbs were made for thin, dry, sandy soils. This is one situation where improving the soil with organic matter is not required. Lavender, thyme and rosemary will cope just fine – in fact they’ll be happier – with a low-fertility bed that never becomes waterlogged in winter.

Most shallow-rooted plants tend to dry out very fast on sandy soils, and brassicas will struggle in the loose, acidic conditions. That’s not to say they can’t be grown, but they will need much more attention than plants that are more suited to growing on sand.

The best vegetables to grow on sandy soil are those that can be grown right through the winter, because they help to bind the soil with their roots and protect it from wind, rain and snow with their leaves. Or sow an overwintering green manure. Even a carpet of weeds will do. What better excuse for delaying that final autumn weeding session?