If you’re leaving home for a few days and want to keep your houseplants happy, you may have tried using a watering globe – those glass bulbs with long stems that slowly release water for your plant. And if you have used one, you’ve probably noticed what a pain it can be to fill. Pour water down the neck too quickly and you’ll get splashed by a sheet of water blown back at you.
That splashback happens for the same reason that blowing across the top of a bottle plays an audible note: you’re compressing the air inside the container. When water tries to pour continuously down the watering globe’s neck, it can block the escape path needed by the air already in the globe. The increasing weight of water atop that volume of air compresses it, raising its pressure until it’s eventually high enough that it blows all the water back out the neck and into your face.
The best method to ensure that doesn’t happen is to fill the globe slowly. Try tilting it at an angle and letting only a small stream of water fall into it such that there’s always an escape route for the air. (Image and video credit: E. Challita et al.)