Start with what you already have

A dye garden rarely begins with a raised bed and a plan drawn on graph paper. More often it starts with a bag of onion skins in the freezer and a south-facing windowsill that could be doing more. The good news is that most of the plants worth growing for colour are tolerant, generous and perfectly happy in containers. A balcony two metres wide can supply you with enough marigolds for a silk scarf, and a single deep pot can raise madder roots worth the wait.

Before you buy anything, work out two things: how much direct sun your space receives, and how much weight it can take. A balcony rated for pots is not the same as one rated for a small tree. Roughly speaking, a 30-litre pot filled with damp compost weighs around 30–35kg, so group heavier containers over load-bearing walls rather than in the centre of a balcony floor. Windowsills are sturdier but offer far less light than you think, especially between October and March.

Then choose plants that suit the space rather than forcing the space to suit the plants. Annuals for pots, deep-rooted perennials for the ground or for one big container, and kitchen waste for free colour all year round.

Pots, compost and drainage that actually work

Terracotta looks beautiful but dries out alarmingly fast in wind, which most balconies have in abundance. Glazed ceramic, frost-proof stoneware or even sturdy plastic with a decent rim all hold moisture better. Whatever you choose, drainage matters more than material: a generous layer of crocks is not a substitute for drainage holes, so check every pot before filling it.

• Annual flowers (marigold, coreopsis, calendula): 5–10 litre pots, peat-free multipurpose compost with a handful of horticultural grit.
• Leaf and tops crops (weld, dyer's chamomile, woad): 10–15 litres, John Innes No. 2 mixed with multipurpose for a bit of weight and structure.
• Root crops (madder, alkanet): 30–40 litres minimum, and at least 40cm of depth. Mix in John Innes No. 3 and grit so the roots run straight and lift cleanly.

On balconies, swap a third of the compost for coir to cut weight without losing water-holding capacity. Add a slow-release organic fertiliser at planting, then top up with a liquid feed every fortnight from midsummer. Saucers under pots protect your neighbours below, but empty them after rain so roots do not sit wet.

Light, warmth and the plants that reward a windowsill

Most dye plants want at least six hours of direct sun. A south-facing balcony delivers that from March to September; an east-facing one gives you gentler light and better results with leafy plants. Marigolds are the easiest starting point — Tagetes patula and Tagetes erecta both germinate in a week on a warm sill and flower within ten weeks from a March sowing. Coreopsis tinctoria is just as straightforward and gives a clear, warm yellow-orange from the flowers alone.

Calendula will flower in partial shade and self-seeds obligingly in pots, though its colour is softer and more buttery than marigold. Sow any of these direct in April or start them indoors in February and harden them off after the last frost, which in most of the UK means late May.

Onion skins need no light at all — they need a kitchen. Save the papery outer layers from red and yellow onions in a paper bag in a cool cupboard, and you will have a rich amber-to-russet dyebath whenever you want one.

Roots, patience and the longer game

Madder is the plant that turns a small-space dye garden into something serious. It needs three growing seasons before the roots are worth lifting, and it wants deep, well-drained, slightly alkaline soil in full sun. A 40-litre pot sunk into a corner of the balcony will do, though it will need staking against wind and a feed of comfrey or seaweed through summer.

Weld and woad are biennials and behave differently. Weld gives the brightest, most lightfast yellow of any plant you can grow in Britain, and a single 12-litre pot will produce enough flower spikes in its second summer for several dye baths. Woad forms a long taproot and resents being moved, so sow it where it will stay and give it 20 litres or a spot in the ground. Both self-seed freely, which is a gift in a small garden — let a few go to seed and you will never need to sow them again.

A simple seasonal rhythm

• February–March: sow marigold, coreopsis and calendula indoors; top-dress overwintered pots with fresh compost.
• April–May: harden off seedlings, plant out, sow weld and woad direct.
• June–September: harvest flowers every few days for the freshest colour, water daily in heat, feed fortnightly.
• October–November: lift madder after three years, cut weld stems for drying, save seed.

Dry surplus flowers and roots in paper bags in a warm, airy room, and label everything with the year. A jar of dried marigold heads in November is worth more than you would think when the pots outside are bare.

Keep it generous, keep it small

The joy of a container dye garden is that it asks very little and gives back in colour you can hold. Start with three pots this year — one for flowers, one for leaves, one for roots — and let the space tell you what it wants to grow. A balcony, a windowsill and a bag of onion skins is a perfectly respectable beginning.