Is summer rain a spa for houseplants?

Indoor plants often collect dust on their leaves, mineral deposits on their soil and a general staleness from sitting in the same spot in poorly ventilated air for months at a time. Giving plants time in warm summer rain is billed as a spa day: soft water reaches their roots, dust is washed from foliage and they get a rare dose of outdoor conditions.

The suggested method is simple: wait for a warm day when the outside temperature is close to what your plants experience indoors, move them to a spot sheltered from wind, let them enjoy the shower for about 20 minutes, then bring them back inside once the rain stops; do not leave them out overnight or in a prolonged downpour.

I tested this with some tropical specimens during what looked like a light summer shower, but the rain proved colder than expected. One Calathea returned with darkened patches on its leaves, a Monstera fared better but had clearly been buffeted, and the others were untroubled.

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