How to improve sandy soil so it holds water

Sand isn't bad soil, it just lets go of everything

Sandy soil warms up early, drains after rain and is easy to dig, all of which are genuinely good, and then it undoes all of it by letting the water straight through and taking the fertiliser with it. So the plant is thirsty two days after you watered and hungry a fortnight after you fed it, and it isn't because you're doing anything wrong, it's because the soil has nothing in it to hold on with.

Everything below is about giving it something to hold on with.

Organic matter, and keep doing it

This is the fix, and the reason people give up on it is that it isn't a one-off. Organic matter breaks down faster in sand than in clay because there's more air in there, so a bed you improved two years ago has quietly gone back to sand. Put something through it every season and you'll stay ahead of it.

Compost is the general answer and it does two jobs at once, holding water and holding nutrients where the roots can reach them. Well-rotted manure does the same and feeds at the same time. Both of them want digging through the top 200mm rather than sitting on the surface, because sand won't drag it down for you the way a worked clay soil will.

Don't bother adding clay unless you're prepared to do it properly. Small amounts of clay through sand can set harder than either one on its own, and it's a bigger job than it sounds.

Water differently, not more

Deep and less often beats a daily splash, because a shallow watering on sand never reaches past the top 50mm and the roots stay up there waiting for it. Give it a long slow soak and the roots follow the water down, which is what you actually want.

Sand also goes water repellent easily, especially under a dry summer, and when it does the water runs off the surface of a bed that looks like it should be soaking it up. A wetting agent sorts that out, and mulch on top keeps the surface from baking dry again.

Feed little and often

A big dose of soluble fertiliser on sand is mostly a donation to the water table. Slow-release and pelletised feeds hold on much better, and a liquid feed every couple of weeks in the growing season suits sand better than one heavy application in spring.

Or work with it

Plenty of things are perfectly happy in free-draining sand and will do better there than in the heavy stuff. Rosemary, lavender, kangaroo paw, coastal banksia and most of the Mediterranean herbs all want exactly those conditions, and putting them in the sandy end of the yard saves you improving ground you were never going to use for vegetables anyway.

Save the compost and the effort for the beds you're actually growing food in. That's the honest version of soil improvement on a sandy block, and it's a lot less work than trying to fix the lot.

Shop related products

• Brunnings Garden Compost with Seaweed 25L. The main one. Dig it through rather than spreading it on top.
• Naturally Good Cow Manure 25L. Holds water and feeds while it does it.
• Naturally Good Mushroom Compost 25L. Good bulk organic matter, and it brings a bit of lime with it.
• Easy Wetta Garden Mulch 50L. Mulch with the wetting agent through it, which is the pairing sand needs.
• Neutrog Rapid Raiser 20kg. Pelletised, so it releases slowly instead of washing through.

Did you know we also stock Easy Wetta wetting crystals in a 500g pack, Nincompoop, pea straw bales, and bagged gypsum for if it turns out the problem is clay at the other end of the yard rather than sand. None of those are on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

It's all in the garden centre, and bring a handful of the soil in with you if you like. It's a lot quicker to tell you what you're dealing with holding it than reading a description of it.

More from the garden

• How to build better soil in any garden
• What to do when your soil is too acidic or alkaline
• How to stop soil washing off your garden beds

My sandy bed is where everything I can't keep alive anywhere else ends up, and it is easily the best looking part of the garden.

Candeece

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