I was in the basement last weekend planting the last of my amaryllis bulbs, and decided I’d better check on the dahlia tubers. If you have tubers stored away for next spring, this is a good time to see how they’re doing.
The key to successfully overwintering dahlias is to keep the tubers properly hydrated. When spring comes, you want them to be the same way they were in the fall: nice and firm like a freshly dug potato. The goal is to maintain a steady state. Too much moisture and the tubers will get mushy and rot. Too little and they shrivel up like mummies. The best way to store them is in a box filled with peat moss, wood shavings or sand.
I have stored dahlia tubers in peat moss and it works great. But now I use a simple technique that works pretty well and saves a lot of fuss.
Since I wait until spring to divide the tubers, they’re stored as clumps, just as they were dug from the ground. If the soil was wet when they were dug, I let them dry for a week or so. If not, each clump — with some soil still attached — goes right into a plastic grocery bag along with the label. This makes it easy to keep the varieties separate and not get the names mixed up. I recently saw a creative solution for tracking which clump is which: tie a piece of survey tape around each clump and use a marker to write the variety name on the tape.
Once the clumps are in their own plastic bags, I nestle 5 or 6 bags together (with the tops open) in one layer at the bottom of a big, black plastic trash bag. The top of that trash bag gets loosely gathered, but stays partly open for ventilation. This bag-in-bag technique is fast and works well, though I often lose a clump or two. If you have prized varieties, I’d recommend sticking with the peat moss. Remember that it’s also important for dahlia tubers to be stored cool, but not cold: 40-50°F is ideal.
When I checked the bags last weekend, most of the tubers looked great — like the clump shown at the top of this post. Some were a little wrinkled, so I put a few handfuls of moist growing mix into those bags and hopefully they’ll rehydrate.
I didn’t save all of the dahlias from last year. Only my favorites. The problem is, every year that favorites list gets a little longer…
If you’d like to learn more about growing dahlias, you may be interested in: