NOTES — RESEARCH NOTES
Heat and ColdHEAT AND COLD
Summer Leaf ScorchSUMMER LEAF SCORCH
Leaf scorch is less about light intensity alone than about conditions stacking up. A plant whose roots cannot take up water has no margin for transpirational cooling, and under strong sun on a very hot day the leaf tissue is damaged by heat. Japanese growers and sellers likewise warn that strong summer sun and afternoon sun cause scorch, while plants hardened to outdoor light rarely burn even in direct sun. A sudden change does it too — a plant wintered indoors put straight out into midsummer sun.
Direct sun on wet leaves is another condition to avoid. The familiar claim that droplets act as lenses and burn leaves is contested, and experiments have ruled it out for smooth leaves. But where hairs hold a droplet up off the surface, focused light can burn the tissue beneath (Ádám Egri and co-authors, 2010). A Dyckia leaf is covered in trichomes (peltate scales), a surface droplets readily sit on. Watering and heavy rain also strip the trichomes themselves, weakening the very layer that reflects the light — our own records include trichomes nearly stripped by heavy rain (Growing Dyckia). The Japanese sellers' advice to water at the base of the plant, not over the leaves, makes sense on this count too.
Winter ColdWINTER COLD
As a genus, Dyckia is among the hardier bromeliads, and some species tolerate brief spells below freezing when dry. But tolerance varies greatly by species, and the same genus includes tender plants such as Dyckia marnier-lapostollei, which dislikes anything near freezing. "The genus is hardy, so every species can winter outdoors" is a mistake.
The state to avoid most is the roots freezing while still wet. The 5 °C guideline — once days below it continue, move the plants indoors or under cover and let them dry — is best understood as a safe-side figure that also assumes shelter from frost.
Researched: October 2026