Wash-day, rescheduled.

Thursday evening, thirty-five minutes.

Step one · The decision — Wash two days before the day that matters.

Work backwards from the day you need your hair to be good and count back two. If that is a Monday presentation, you are washing on Saturday evening. If your week has no fixed shape, Thursday is the safest default: day two lands on a Saturday, and day three on a Sunday, which is the day you can most afford a low bun. Evening rather than morning, and early enough that it dries before you sleep — wet hair swells, and swollen hair against a pillow for seven hours is where the midshaft breakage comes from.

If it has to be a morning wash, wash the night before anyway and re-wet only the front section in the morning. Nobody has ever noticed.

Step two · Not every wash — Clarify once a fortnight, not once a week.

A clarifying shampoo is designed to strip, and it is very good at it — silicone build-up, styling polymer, the calcium and magnesium your tap water leaves behind. Used every wash it takes the colour and the softness with it, which is why people call their clarifying shampoo drying and then keep using it weekly. Once every three or four washes, scalp only, a minute, rinsed properly.

Hard water tells on you: thin lather, ends coated two days after a wash. That is minerals rather than product, and the clarifying wash is the fix.

Step three · Ten minutes, unattended — Conditioner from the ears down.

Squeeze the water out of the hair first — conditioner on soaking hair is conditioner going down the drain in dilute form. Then apply from roughly ear level down, comb it through with your fingers, twist it up, and leave it for ten minutes while you do something else. Shower steam does more for penetration than any device sold for the purpose. Rinse until the mid-length squeaks slightly and no further.

Ten minutes is the number. Two minutes is a rinse-out conditioner with delusions, and thirty minutes does nothing that ten did not already do.

Step four · Damp, not wet — Heat protectant, then rough-dry to eighty per cent.

Let the hair get to genuinely damp before the protectant goes on — a spray onto sopping hair mostly lands in the water. Then rough-dry on medium heat, dryer about fifteen centimetres away, to around eighty per cent, and finish with cool air or leave it. Heat protectant raises the temperature at which damage starts; it does not make hair fireproof, and a straightener on damp hair will boil the water inside the shaft whatever you sprayed on first. That sound it makes is the point being proved.

If you are air-drying entirely, still use the protectant. The sun on a Saturday afternoon is heat too, and the slip makes the comb-through easier.

Step five · The night before — Dry shampoo goes on before the grease arrives.

This is the change that surprised me most. Dry shampoo applied on the evening of day two, to roots that are not yet oily, has all night to sit where the oil is about to be, and by morning it has absorbed it rather than sat on top of it. Twenty centimetres away, in sections, then brushed through and forgotten. Applied at 8am to hair that has already gone, it is powder on grease and it reads as powder on grease. It is the same argument I made about the pillowcase — a night is eight hours of your hair being handled whether or not you are awake for it.

Brush it through with a natural bristle brush before bed. The oil that is already there gets pulled down the length, which is where you want it anyway.

The shelf — what this actually needs

• A clarifying shampoo, used every third or fourth wash
• A deep conditioner that can sit for ten minutes
• A heat protectant, sprayed on damp hair
• A dry shampoo, applied the night before
• A natural bristle brush

What’s in it

• Chelating agents — What makes a clarifying shampoo clarifying. They bind the calcium and magnesium your tap water leaves in the hair.
• Rice or tapioca starch — The absorbent part of a dry shampoo. It works on oil that arrives after it, which is the case for applying it at night.
• Silicones — Excellent slip, real build-up. Not a villain, but the reason the clarifying wash exists.
• Fatty alcohols — Cetearyl and behenyl in a conditioner. They soften rather than dry, whatever the word alcohol suggests.

How to know it is working.

You are looking for the good day to have moved, not for the hair to have changed. Give it three weeks — the first week of any new schedule is your scalp adjusting to a different frequency, and it will overproduce briefly to make its feelings known. Judge it on a day two.

• Day two now lands on the day you need it, and you did nothing to it that morning beyond a brush.
• Day three roots look like day two roots, because the dry shampoo went on the night before.
• The ends feel the same on day four as they did on day one, which means the conditioner is staying put and the clarifying wash is not too frequent.
• If the roots are gone by the end of day one, you are washing too often and your scalp has adapted. Stretch by one day at a time, not three.
• If the length feels coated within two days of a wash, that is build-up or hard water, and the clarifying shampoo has been left out too long.

If the week keeps slipping.

My hair is oily by the end of day one. Does this schedule work for me?

It works, it just runs shorter. Wash the evening before the day that matters rather than two evenings before, and use the dry shampoo on the night of day one instead of day two. What does not work is washing every morning to stay ahead of it — a scalp washed daily produces on a daily cycle, and stretching it takes about three weeks of mild irritation before it settles.

Can I sleep on it wet if I braid it?

A braid reduces the friction but not the swelling, and wet hair is at its most fragile in exactly the state you are then compressing for seven hours. If you are out of time, get it to eighty per cent dry with a dryer and braid it loosely. A silk pillowcase helps here for the same reason it helps everywhere else, which I have written about at length elsewhere.

Is the clarifying shampoo really necessary if I use gentle products?

If your water is soft and you use little product, probably not — go monthly and see whether anything changes. Hard water is the deciding factor rather than your shampoo, and you can usually tell by the state of your kettle. The minerals bind to the hair whatever you wash with.

Does the deep conditioner need heat to work?

Not a device. Shower steam and a twisted-up length under a towel keep it warm and damp for ten minutes, which is all the heat does. A heated cap is a warm towel with a plug on it.

I keep forgetting the dry shampoo at night. Any way to make it stick?

Keep the can where you brush your hair before bed rather than in the bathroom cupboard with everything else. It is a one-second decision that only happens if the object is in front of you. The morning version of this decision does not exist, because in the morning it is already too late.