Why mix your own?

Bagged compost has become expensive, and quality varies wildly from batch to batch. If you have a bit of space — a corner of a shed, a plastic trug, a dustbin with a lid — you can blend a potting mix that outperforms most shop-bought bags for a fraction of the cost. The real benefit isn't money, though. It's control. You know exactly what your roots are sitting in, and you can adjust it for the plants you actually grow: greedy tomatoes, delicate cuttings, rosemary that sulks at the first sign of damp.

Roots need three things from a mix: moisture, air and anchorage. Get the balance wrong and you'll see it in yellowing leaves, stunted growth and the sour smell of a waterlogged pot. The answer is a free-draining blend with enough body to hold together and a texture that lets water pass through rather than sit.

The three core ingredients

Almost every traditional mix in Britain comes down to three things, combined in different proportions.

• Loam — the backbone. This is good-quality, well-rotted turf or topsoil, the crumbly dark stuff that smells of a woodland floor. It holds nutrients and water without turning to sludge, and gives the mix weight so taller plants don't topple. Sieve it to about 6mm before use.
• Compost — homemade or bought, well-rotted and sieved. This supplies nutrients, feeds soil life and lightens the mix. Leafmould and worm compost both work well; leafmould is especially good for woodland plants and ferns.
• Grit — horticultural grit of 3–4mm, or sharp sand. This is the drainage engine. It opens up the mix so air reaches the roots and surplus water drains away. Perlite does the same job if you prefer a lighter mix, though it floats to the surface over time.

Whatever you use, never fill pots with unamended garden soil. It compacts in containers, drains poorly, and brings in weed seeds and grubs.

Simple recipes by volume

Use a bucket, a jug or an old mug — just keep the measure consistent. Ratios are by volume, not weight.

• General purpose: equal parts loam, compost and grit. This suits most shrubs, perennials, herbs and container veg.
• Sowing seeds: two parts loam, one part compost, one part fine grit, sieved to a fine tilth. Lower nutrients prevent seedlings scorching.
• Cuttings and succulents: equal parts loam and grit, with just a handful of compost. Sharp drainage is everything — most cuttings rot before they root in a rich mix.
• Hungry feeders: two parts compost to one part loam and one part grit. Tomatoes, courgettes and dahlias respond well, though you'll still need to feed from midsummer.

Add a slow-release fertiliser or a few handfuls of sieved garden compost if your loam is old and tired. A sprinkle of lime helps brassicas and most veg, but skip it for acid-lovers such as blueberries, camellias and rhododendrons.

The squeeze test

You can judge a mix by hand faster than by eye. Take a fistful, squeeze it firmly, then open your hand.

• If it holds its shape but crumbles when you poke it, the texture is about right.
• If it stays in a slick, wet lump, add more grit.
• If it falls apart instantly and feels dusty, work in more compost or loam.

Aim for something that feels like coarse crumbs with a few visible grit particles. When you water a finished pot, water should run out of the drainage holes within a few seconds, not pool on the surface.

Sieving, storing and hygiene

Sieving is the least glamorous job and the one that makes the biggest difference. A garden sieve with a 6mm mesh takes out stones, twigs and lumps, and gives you a mix that fills pots evenly and holds moisture predictably.

Store mixed batches in a lidded bin or old compost sack, somewhere dry, and use within a season or two. If you're reusing pots and trays, scrub them and rinse with hot water first — a surprising amount of damping-off and root rot starts with dirty containers rather than bad compost. If you want to sterilise a batch of loam, spread it in a tray and warm it through in an oven at around 80°C for half an hour. Let it cool fully before sowing, or you'll cook your seedlings.

Fine-tuning for your own garden

Every garden is slightly different. Heavy clay loam needs more grit; sandy loam needs more compost to hold moisture. Once you've made a few batches you'll stop measuring and start mixing by feel. Keep a notebook, jot down what worked for which plants, and adjust next spring.

Above all, remember that roots breathe. A mix that drains freely, holds moisture without drowning it, and smells sweet and earthy will reward you with sturdier plants, stronger growth and far fewer disappointments when the wet British weather sets in.