Tradescantias are semi-succulents, which means they’re much more tolerant of drought than a lot of plants. It also means that they’re a lot less obvious about it when they eventually do get thirsty. Growing tradescantias as houseplants is very different from having “drama queens” like coleus, nerve plants, and polka dot plants.
Tradescantias won’t dramatically wilt and fall over when they’re thirsty, but they will show more subtle signs. Here’s a picture of two stems of T. mundula ‘Green Hill’ – one of them is thirsty, and the other is well-hydrated. There are two good features to look for.
First is the colour. When a tradescantia is healthy and well-hydrated, its leaves will be bright and strongly coloured. Even in a plain type like this, the green is rich and saturated. When the plant is thirsty, all the colours will fade and become dull, pasty and greyish.
The second is the texture. A well-hydrated tradescantia has leaves with just a slight satiny sheen. But when it gets very dry, the leaves become extremely glossy and reflective, almost like they’ve been coated in varnish.
If you’re new to tradescantias, I’d recommend deliberately letting your plants get really dry a few times, so that you can learn to recognise these signs yourself! Once you have a sense of how the plant looks when it’s extremely dehydrated, you’ll be more able to recognise when it’s just starting to get thirsty and needs watering. And because they’re semi-succulents, they’ll recover easily from drying out with no real harm done.