If the soil you added the sand to was clay-based, the sand might worsen drainage unless it's used in a much higher concentration. Organic matter like compost tends to be a more effective soil additive in that case to improve drainage. Penstemon varieties like this one need excellent drainage to thrive, even though they are often naturally short-lived anyway. Make sure the new plants are checked for watering needs periodically (even in winter, when it's thawed enough to feel the soil moisture a few inches down), but don't keep the plants damp.

The "parent" variety that this cultivar was selected from is rated less cold-hardy than 'Cherry Sparks', and we aren't familiar enough with that variety to know how reliably well it overwinters here, both due to cold exposure and a tolerance for our heavier soils than the types of habitat where these Penstemon would naturally grow. On paper, the plant is cold-hardy enough to be okay in our winters without any special measures, but in practice, sometimes soil conditions (insufficient drainage, typically) or summer stress from heat and humidity can shorten their lifespan to just a couple or so years.

Miri