Which compost for which job, how much, and when — no waste, no guesswork.
Which compost for which job
The job
Use this (peat-free)
Why
Sowing seeds
Fine seed / peat-free multipurpose
Low nutrients + fine texture so seedlings root easily
Pots & containers
Multipurpose + John Innes No.2/3
The loam holds water & feed for the long haul
Raised beds & borders
Soil improver / well-rotted manure
You're feeding soil, not filling a pot — cheaper per litre
Blueberries, rhododendrons
Ericaceous compost
They need acidic soil — ordinary compost slowly starves them
How much do you need?
Topping a raised bed: our raised-bed ratio is 30–40% compost over 60–70% topsoil. A 2m×1m bed at 25cm ≈ 150L compost over 350L soil.
Pots: a 40cm patio pot holds roughly 40 litres.
Don't eyeball it — the compost calculator gives your exact litres and bag count.
Peat-free behaves differently
It dries out faster on top — check with a finger, water a little more often.
It runs out of feed sooner — start liquid feeding pots after about 4–6 weeks.
Lumpy bag? Normal for peat-free — break up big bits before sowing fine seed.
The £-saver
Buying the right amount once beats two trips and a half-used bag going hard in the shed. Big beds? Bulk bags of soil improver are far cheaper per litre. And many UK councils sell cheap green-waste compost — fine for beds, not seeds.