Dyeing with what the garden already gives you

There is a particular satisfaction in pulling a skein of wool from a pot of simmering onion skins and watching it emerge the colour of honey and old brass. Natural dyeing asks very little of you in the way of equipment and nothing at all in the way of shop-bought colourants. Most of what you need is already growing in the garden, lurking in the kitchen bin, or flourishing along the hedge bank at the end of the lane.

Before you begin, set aside a few rules of good practice. Keep dedicated dye pans, spoons and buckets that never return to the kitchen. Work outdoors or in a well-ventilated shed, wear gloves, and keep powders away from your face. Stainless steel and enamel are ideal; avoid aluminium and chipped pans, which can alter your colours unpredictably.

Mordants: the quiet chemistry that makes colour stick

Without a mordant, most plant dyes wash straight back out of the cloth. A mordant is a metal salt that binds the dye to the fibre, and the two you will use most often are alum and iron.

• Alum (potassium aluminium sulphate) is the gentlest and most reliable. Use roughly 10–15% of the dry weight of your fibre, plus a spoonful of cream of tartar, dissolved in enough warm water to cover the goods.
• Iron deepens and saddens colours, turning yellows to olive and browns to charcoal. Make your own "iron water" by steeping a handful of rusty nails in a jar of water and white vinegar for a fortnight, then use it a tablespoon at a time. It is harsh on wool, so add it after dyeing rather than before.
• Tannins are essential for cotton, which has no natural affinity for most dyes. Simmer the cloth first in strong tea, oak galls or sumac leaves, then mordant with alum.

Wool is mordanted gently — bring it slowly to around 80°C and hold it there for an hour without boiling, or you will felt it. Cotton needs scouring first, boiling with a little washing soda to strip away the natural waxes. Never tip spent mordant baths onto the garden; let them cool, dilute heavily, and dispose of them responsibly.

Onion skins: the dependable beginning

Save every skin from your brown onions through the year and keep them in a paper bag. You want roughly equal weights of skins and dry fibre, though two to one gives a richer result. Simmer the skins in soft water for an hour, strain, then add your mordanted wool and hold it at a bare tremble for another hour. Alum gives a warm apricot-orange; a dash of iron water afterwards shifts it towards a deep tobacco brown that suits tweed and winter knitting.

Marigolds: sunshine in a pot

French and African marigolds flower prolifically from midsummer until the first frost, and they give some of the loveliest golds and soft greens in the dyer's palette. Pick the heads as they begin to fade, and dry them on a tray if you are not dyeing straight away. A generous couple of handfuls per 100g of wool, simmered for forty minutes, produces buttery yellows on alum-mordanted fibre and clear olive greens with iron. Calendula petals give a paler, softer yellow that fades gracefully — beautiful on silk and fine cotton.

Nettles: the hedgerow stand-by

Pick young nettle tops in April and May, before the plants flower, wearing thick gloves and taking only the top four leaves from each stem. Simmered for an hour, they yield a soft sage on alum-mordanted wool and a clearer green when the fibre has had a tannin pre-treatment. Add iron and you get a dignified grey-green that looks wonderful on hand-knitted socks and garden sweaters. Older nettles give duller, browner results, so catch them young.

Keeping a dye notebook

Natural dyeing is endlessly variable — the same plant on the same day can give three different shades depending on water hardness, pan, and the mood of the weather. A simple notebook is the single most useful tool you own. Record for every batch:

• The date, plant and part used, and where it came from
• Weight of plant material against weight of dry fibre
• Mordant, quantity, and whether it was applied before or after dyeing
• Temperature, timing, and any modifiers such as iron or vinegar
• A small labelled sample of the finished yarn, sewn in with a needle and thread

Add a note on how the colour stands up to washing and light after a month, and you will soon build a personal record far more valuable than any published chart. Start with onion skins, work up to marigolds and nettles, and enjoy the slow, quietly addictive pleasure of colour drawn straight from the soil.