Brunnings Garden Compost with Seaweed, what it actually does

When water runs straight off the bed instead of into it

If you water a bed properly and then scratch the surface an hour later and find it bone dry 3cm down, the soil hasn't failed to hold the water, it's refused to take it in the first place. That's water repellent soil and it's common on the sandier ground around here. It happens because waxy residues off old roots and fungi coat the sand grains until water beads up and runs off sideways looking for a crack.

What the compost is doing about it

Brunnings Garden Compost with Seaweed works on that in two ways at once. The organic matter itself holds many times its own weight in water and gives the sand something to hang on to, and it feeds the soil life that eventually breaks the waxy coating down. The first effect you get straight away. The second one takes a season or two and it's the one that actually lasts.

The seaweed in it is a soil conditioner rather than a fertiliser, so go in expecting better structure and a bit of trace element rather than a growth spurt. A compost is not a feed and the bag doesn't pretend it is.

You need far more of it than you think

This is where most people go wrong and then decide compost doesn't work. A bag spread thin over a whole bed does almost nothing, because you're aiming to lift the organic matter content of the top 15cm of soil by a few percent and that takes volume.

As a rough working figure, a 25 litre bag spread 2cm to 3cm deep covers about a square metre. Dig that through the top 15cm and you've genuinely changed that square metre. Do a small area properly rather than a big area lightly, and come back and do the next bit next time. Soil that's been fed every year for 5 years is a different thing to soil that got one bag once.

Where it goes

• Dug through the top 15cm of a bed before you plant, which is the version that fixes the repellency.
• Spread as a thin layer around established plants and watered in, where you can't dig without wrecking roots.
• Into the backfill when you're planting a tree, mixed with the soil that came out rather than used neat.
• Over the top of a bed but under a proper mulch, which is the arrangement that works best of all.

Compost is not a mulch, whatever the bag looks like

Compost left on the surface on its own dries out, crusts over and then sheds water much like the soil you were trying to fix. It's also a beautiful seed bed, so every weed seed that blows in gets a soft damp landing pad and you spend the next month pulling them out.

Use compost as the conditioner underneath and something coarse on top as the actual mulch. Coarse material lets water through, breaks down slowly and doesn't give weed seed anything to germinate into. Keep whatever you use 5cm clear of stems and trunks, because mulch packed against bark holds moisture where it does damage.

Don't plant straight into neat compost

Compost out of a bag is concentrated and it isn't soil, so a seedling put directly into it can sit in something that stays wetter than it wants and holds more nutrient than a young root can handle. Mix it through the soil that's already there. The point of it is to improve the ground, rather than to replace it.

Shop related products

• Brunnings Garden Compost with Seaweed 25L. Organic matter plus a bit of trace element from the seaweed.
• Brunnings Ultimate Dig It In Compost 30L. A bigger bag for when you're doing a whole bed.
• Naturally Good Mushroom Compost 25L. The other one people reach for, and it runs on the alkaline side.
• Manutec Soil pH Test Kit. Worth knowing where you started before you add anything by the barrow load.

Did you know we also carry mulch in the shop, in lucerne bales and in compressed blocks, which is what you want going over the top once the compost is in. The mulch isn't listed on the website, so give us a ring on (08) 8536 4333 to check what's on the shelf, or come and see what's in the garden centre.

Read next

• How to improve sandy soil so it holds water
• How to build better soil in any garden
• Whoflungdung, what it is and when to use it

I buy compost in quantities that look ridiculous in the back of the ute, on the grounds that I have never once regretted putting too much organic matter into a bed.

Cheers,
Candeece

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