Why Linen and Wool Ask for Something Different

Both fibres come from the natural world, but they behave very differently once they meet water. Wool is protein — keratin, the same family of material as your own hair — and each fibre is covered in microscopic scales. In an alkaline solution those scales lift and lock together, which is how a favourite jumper quietly becomes a child's jumper. Linen is cellulose, spun from flax, and it is far tougher: it tolerates warmth and a little alkalinity, but repeated exposure to harsh detergent leaves it brittle, grey and limp.

That gives you two rules of thumb. Wool wants a neutral to slightly acidic wash, around pH 6 to 7, with minimal agitation and no sudden temperature changes. Linen wants a gentle surfactant that lifts soil without stripping the natural pectins and waxes responsible for its quiet sheen. Neither fibre needs the aggressive chemistry designed for grubby cotton towels.

What "Plant-Based" Really Means on a Label

A plant-based detergent is built around surfactants derived from plants rather than petrochemicals. The most common are sugar-based glucosides (coco-glucoside, decyl glucoside) and true soaps made from olive, sunflower or coconut oil. Both biodegrade readily and are kind to septic tanks and greywater systems.

What matters just as much is what has been left out. Watch for these on the ingredients list:

• Protease enzymes — brilliant on food stains, disastrous on wool, because they digest protein. That means holes and thinning.
• Cellulase enzymes — designed to smooth cotton by nibbling away surface fuzz, but linen is cellulose too. Over time it weakens the cloth.
• Optical brighteners — fluorescent dyes that sit on the fibre and glow. They do not clean, and they build up on linen, dulling its natural colour.
• Chlorine bleach, phosphates and EDTA — hard on fibres, hard on waterways, and unnecessary for day-to-day washing.

A genuinely good plant-based liquid is usually pH-adjustable, free of enzymes, and carries a "readily biodegradable" claim rather than a vague promise about the planet.

A Practical Comparison of Plant-Based Options

• Sugar-surfactant liquids: the best all-rounder for wool and linen. Mild, effective even in hard water, and easy to dose in small amounts.
• True soap liquids (castile, olive or sunflower based): superb on linen and very gentle on skin, but they form scum in hard water and can leave a grey film. Pair with a water softener, or save them for soft-water areas.
• Soap nut liquor: naturally near-neutral and rich in saponins, lovely for delicates and woollens. Weaker on oily stains, and it spoils quickly, so make small batches and keep it cool.
• Plant-based powders: usually built with sodium carbonate, which is alkaline. Fine for sturdy linen in a hard-water area, but too harsh for wool.
• Capsules: convenient but fixed-dose, and the film may not dissolve in a cool wool cycle. Pour-over liquids give you far more control.

Dosing: The Skill Nobody Teaches You

Overdosing is the single most common laundry mistake, and it is worse with natural fibres. Excess detergent does not rinse away; it stays in the cloth, attracting dirt, stiffening linen and leaving wool feeling tacky. It also sends a needless load of surfactants into the water course.

• Soft water (much of Scotland, Wales, the south-west and Northern Ireland): begin with 15–20 ml of a concentrated liquid for a 4–5 kg load.
• Hard water (much of the south-east, the Midlands and East Anglia): 25–35 ml, or 20 ml plus a plant-based water softener such as sodium citrate.
• Wool: use roughly half the recommended dose. Wool holds far less soil than cotton and mostly needs lubrication between the fibres.
• Half loads: halve the dose. A full cap on a small load is a residue problem waiting to happen.
• Always measure with the cap or a jug, level off, and resist the glug.

If linen comes out stiff or woollens feel flat, the answer is usually less detergent, not more — plus an extra rinse.

Getting the Wash Itself Right

Detergent is only half the story. Wash wool on a dedicated wool programme or by hand at 30°C with a spin no faster than 400–600 rpm, and never plunge it from warm water into cold. Linen can take 40°C happily, and 60°C occasionally for whites, though cooler washes protect the colour and the fibre over the long term.

Skip fabric conditioner entirely. It coats the fibre in a waxy film, reducing linen's absorbency and wool's breathability. If you want softness, add 50 ml of white vinegar to the rinse compartment — it restores a slightly acidic pH and helps rinse away soap residue. Do not use it alongside chlorine bleach. Dry woollens flat, reshape while damp, and line-dry linen in the shade to keep it crisp.

What Goes Down the Drain Matters Too

Everything you pour into the drum eventually reaches a river, a reed bed or your own septic tank. Choosing a readily biodegradable, plant-derived detergent is the biggest single difference you can make, but the smaller habits count as well: washing at 30°C, running full loads, and buying concentrates or refills rather than bulky diluted liquids. A concentrated bottle means fewer lorries on the road and less plastic in the cupboard.

Used carefully, plant-based detergents are not a compromise. They keep linen lustrous and woollens soft for years, they leave your skin calmer, and they let the water leaving your home stay clean enough for everything downstream of it.