Phototropism

[loyall]

I am new to cacti, but I am familiar with turning indoor plans to promote symmetry. I believe the tendency of plants to turn toward a light source or sunny window is called phototropism. My question whether there are accepted practices for dealing with it in cacti. This photo shows a Mammallaria microhelia that has doubled in height in the last six months. It had a circle of blossoms about half way up the present stem height in February. I find that I have to turn it 180° once a week to keep it upright. Is this what everyone does? Or is here something different that I should do? I have other cacti that do this too, but less dramatically, such as Parodia magnifica, Parodia erubescens, Parodia leninghausii, and Parodia mammulosa.

[Steve Johnson]

Cacti don't rotate their roots in the wild, and I could never understand why growers want to do it with potted cacti. Seems unnatural to me, but that's a matter of personal taste, and there's nothing wrong with rotating your plants -- especially if there's a practical reason for doing it. Maybe for windowsill cacti?

[DaveW]

Yes as Steve says rotation does not happen in habitat, but windowsill growing is not habitat. However one of the problems can be burning from sunlight if the plant is not used to regularly facing the sun that way. Not usually a case with regularly rotated window plants. The other is with some plants it can inhibit flowering. Generally in a greenhouse with full sun exposure and not shielded by trees etc I would not rotate plants. In fact in habitat some cacti naturally lean towards the sun, therefore that is natural growth

However do not confuse the slanted crown in some of those species that uses to be called Eriocactus with leaning, since the plant grows straight up, but it is normal growth for the crown to angle to the sun and is a characteristic of those species and not bad growing conditions.

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[One Windowsill]

You can reduce the need to turn the plant by putting a highly-reflective white or silver curtain behind it during the growing season.

[DaveW]

Kitchen foil?

[One Windowsill]

Kitchen foil?

Foil is remarkably non-reflective, shiny but only about 50% reflection. A bright white cloth curtain would be better. The various specialist silvery reflective plastic sheets are the best but any bright white plastic would do.

[loyall]

Thanks all for the advice. I'm not inclined to put a reflective curtain behind my windowsill cacti because I enjoy being able to see them when I walk by. Cure would be worse than the problem.