How many litres of mulch do I need per m²?

50 litres per square metre at 5cm deep, 75 litres at 7.5cm. A 1,000-litre hippo bag therefore covers 20m² at standard depth — the mulch calculator converts your area and depth into the cheapest bag combination.

Should I remove old mulch before topping up?

Usually not — old mulch is composting into the soil, which is the point. Top up to your target depth each year. Only strip it out if it's matted, sour-smelling or diseased.

When is the best time to mulch?

Spring onto moist, weed-free soil — you lock in winter moisture and smother germinating weeds before they start. Autumn works too, insulating roots before frost. The one mistake to avoid: mulching dry, dusty soil, which just locks the dryness in.

Garden guide

How Deep Should Mulch Be? The Simple UK Guide

Written with Paul. A full-time working gardener. After years in the City, Paul packed it all in, retrained at Writtle College, and has gardened for a living ever since. The “Paul” notes in this guide are his real advice from real jobs.

The quick answer

For most beds and borders, 5–7.5cm (2–3 inches) of mulch is ideal. That's deep enough to smother annual weeds and hold moisture, but not so deep it harms your plants.

Why depth matters

Under 5cm, light reaches weed seeds and they germinate straight through. Over 10cm, water can struggle to reach roots, slugs set up home, and stems rot where they sit against wet mulch.

The right depth for each job

Beds and borders: 5–7.5cm. Around trees and shrubs: 7.5–10cm, kept a hand's width away from the trunk. Veg patch paths: 10cm of coarse wood chip suppresses everything. Containers: 2–3cm — pots dry out fast and only need a top dressing.

Keep it off the stems

Whatever the depth, pull mulch back a few centimetres from plant stems and tree trunks. Constant damp contact is the one way mulch damages plants.

Working out how much you need

You need 10 litres per square metre for every centimetre of depth. A 20m² border at 5cm is 1,000 litres — about one and a half bulk bags. Our mulch calculator does the maths and prices the bags for you.

Paul's note

Mulch is a yearly subscription, not a one-off purchase — it breaks down by a centimetre or two every season. Paul tops up every spring without fail, a light 2–3cm refresh over the old layer, and his beds never drop below the working depth. Skip a couple of years and you're starting from scratch again.

Open the mulch calculator

Common questions

For bark around shrubs and perennials, 5–7.5cm is the sweet spot. Go to 10cm only for serious weed suppression on empty ground — and whatever the depth, keep mulch a hand's width clear of stems and trunks, because constant contact rots bark and stems.