How these cacti flower

The flower is the biggest thing one of these plants ever does, and you get about a day of it. It opens after dark, it is white, it can be as long as your forearm — and by the following evening it is a wet rag hanging off the rib — what Rib means. Anything anyone does with pollen — what Pollen means has to happen inside that window, which is why growers who breed learn to read a bud weeks before it opens.

Spines, branches and flowers all start from the same structure: the small felted pad sitting above the notch on each rib. The ones that flower are the ones near the tip, and a single tip commonly carries two to five flowers at once — eight is not unheard of.

The flower itself is a long cone rather than a shallow cup. Usually 15 to 30 centimetres from base to petal tip, white, occasionally yellow and rarely red, on a tube covered so densely in hair that the bud looks felted. That hair is where the genus got its name, and a hairy bud with a hairy fruit behind it is the fastest way to satisfy yourself that you are looking at a true Trichocereus — what Trichocereus means rather than one of the lookalikes.

A cutting — what Cutting means does the same arithmetic. Faced with more buds than it has stored energy for, it aborts some rather than run itself flat — that is correct behaviour, not a fault. If you would rather the energy went into two flowers than six, pull the extras off with your fingers. The plant will not mind.

It opens at nightfall and it is spent by the end of the next day. Pollen is only worth collecting for a few hours of that — at dusk with the flower fully open, or at first light the next morning — and a flower wet with rain or a heavy dew has pollen you cannot use at all that day.

This is the whole reason breeding these plants turns into a bookkeeping job. Two plants you want to cross — what Cross means have to be in flower on the same night, or you need pollen from one of them already in the freezer.

Two things carry buds through to an open flower: steady moisture and phosphorus. Not floods — steady. A dry spell while a plant is budded is the commonest reason buds drop, so a plant that has decided to flower is one you water more regularly than usual rather than more heavily. Lift phosphorus and potassium in the feed just before and just after dormancy — what Dormancy means and you will see more buds.

Warmth early in the season matters more than most people expect. One collection that moved to a colder climate lost roughly half its flower tufts after a cold May — the tufts appeared, and then simply never became buds.

Late spring into summer, with a second flush often coming through in high summer. Some hybrids ignore the calendar entirely — there is a clone — what Clone means that blooms right through winter. You do not have to engineer a cold dormancy to get flowers, either: plants in mild climates where winter barely registers bloom every year.

An areole — what Areole means that has flowered can flower again from the same spot, so a bloom is not a one-off cost. The only way to lose that position is to tear the fruit off by hand and pull the growing point out with it. Cut fruit away at its base with a blade and the areole lives to do it again.

If a flower is not pollinated, that is the end of it — the whole thing withers and drops away, base included, leaving nothing behind. What happens when it is pollinated is two guides further on, and the guide in between explains why it cannot be pollinated by the plant next to it.