How Much Mulch Do I Need? A Practical Guide

Mulch is the cheapest way to make a garden look looked-after: a fresh layer over bare soil instantly tidies beds, holds moisture and keeps weeds down. The only tricky part is knowing how much to buy — order too little and you're back at the garden centre with thin, patchy coverage; too much and you're tripping over bags all summer. Paul suggests measuring your beds before you even think about ordering: five minutes with a tape measure now saves a wasted trip later.

Mulch vs bark — what's the difference?

Strictly speaking, mulch is the job, not the product: anything spread over the soil surface to cover it is a mulch. Bark is simply the most popular type. Ornamental bark chips look smart and last longest, composted bark or wood chip feeds the soil as it breaks down, and a peat-free soil improver mulches and conditions in one. Paul highlights a common mistake here: paying for premium decorative bark on a big utility bed where a composted mulch would look after the soil better for half the price. Save the ornamental bark for the beds you see from the kitchen window.

The right depth for beds and borders

Depth is where most people go wrong. A token sprinkling of 2–3cm does almost nothing: light still reaches weed seeds and the wind takes half of it. Aim for 5cm as a sensible minimum, and 7.5cm where weeds are your main battle. Keep mulch a hand's width clear of plant stems and tree trunks, though — piling it against bark invites rot.

Measuring awkward beds

Few beds are perfect rectangles, so don't try to measure them like one. Split an L-shaped or curving bed into rough rectangles, measure each in metres, multiply length by width, and add the pieces together. Paul suggests pacing it out if the bed is a strange shape — a normal walking pace is close enough to a metre for mulch maths, and being 10% out changes your order by a handful of litres, not a lorry load. For a circular bed, multiply the distance across by itself and knock off a fifth.

How much to order — the quick maths

The rule of thumb: every square metre takes 10 litres per centimetre of depth. So a 20m² bed at 5cm deep needs 1,000 litres — that's one bulk bag, or around twenty 50L handy bags. The table below gives you a fast reference for typical gardens, and the calculator works out the cheapest way to buy your exact quantity.

Why mulching is worth the effort

A good layer of mulch pays you back all season. It holds moisture in the soil so beds need far less watering through dry spells, blocks the light that weed seeds need to germinate, and slowly feeds the soil as it breaks down. From Paul's experience with garden projects, the beds that get properly mulched in spring are the ones still looking sharp in August — while unmulched beds need hoeing every fortnight and watering every other day.

When to mulch

Mid to late spring is the classic window: the soil has warmed up, there's still moisture locked in from winter, and weeds haven't got going yet. Autumn mulching works well too, tucking beds up before winter. The one thing to avoid is mulching frozen or bone-dry soil — you'd seal in the very conditions you don't want. If you're planning the year's jobs, the UK gardening calendar maps out what to do each month.