I understand a really good additive is sheep manure but think any well rotted manure would do as well. Steve in Baltimore County.

Get a soil test and if you need to adjust the Ph now is the time to do it. Dahlias like a Ph of 6.2-6.8 optimal or 6 to 7.

I was thinking of seeding with crimson clover in my raised bed and tilling under in the spring for organic material. I plan on leaving my tubers in the ground since this is their first year, keep the inverted tomato cages over them as markers so I won't till them by accident in the spring, and putting mulch directly on top of them for warmth. How does that sound for soil prep?