Plants need about an inch of rain per week. A good drink not a sip every day or two. Euphorbias have a long taproot and the water needs to reach it

Use the finger test if you need to. Stick your finger a couple of inches into the soil, if it feels dry, water. By watering only for a few seconds at a time any plant will suffer because there is no reason for the roots to extend deep into the soil the way they should.

I've thought of planting these several times, but I wanted to point out that these are not native to North America. Euphorbia epithymoides (aka E. polychroma) comes from central/southeast Europe, and 'Bonfire' is a patented cultivar (or possibly a hybrid). The Perennials forum would be a better fit for the question.

That said, I've seen some wonderful combinations of this plant with low grasses like Sesleria (also non-US-native) in photos. Nice textural and color contrast.