How To Bring Up Level Of Soil in Bed Without Taking Plants Out

Q: Four years ago we built a large raised bed and planted Asian lilies, canna
lilies, and other perennials. Now the level of the soil mix is four inches lower.
Is there a way to bring the soil level back up without taking all the plants out?

A: Some bulbs have the ability to move themselves down in the soil, using
contractile roots, but I don’t know of any that can move upwards. Too much
soil on top of plant roots will suffocate them. You might get by if you add a
soil mix that is very sandy and breathable. But frankly, removing the plants
after they bloom, adding soil, and replanting would be your best route to raise
the soil level.