How to Store Dahlia Tubers Over Winter

When to dig

Wait for the first hard frost. Frost blackens the top growth and tells the plant the season is over. In cold climates where the soil freezes four to six inches deep, dig by about mid-November or right after that first killing frost, whichever comes first.

You do not have to rush the day after a light frost. The tubers keep maturing in the ground for a week or two after the tops die back. A little longer in the soil can mean firmer tubers and better eyes. Just lift them before the ground itself freezes.

Cut the stems back before you dig, but do it right before, not days ahead. Cut stalks are hollow and will funnel rain or hose water straight down into the crown, where it can start rot. Lift each clump with a fork, digging wide so you do not spear the tubers. Shake or rinse off the soil so you can see what you have.

Curing before storage

Curing lets the skins firm up and the cut or broken surfaces seal over. It is a short rest between digging and packing away. Skip it and you store tubers with open wounds that invite rot.

Set the clumps in a well-ventilated spot out of direct sun. A garage, shed, or basement works. Aim for a temperature around 60 to 70 degrees Fahrenheit for a few days. If you washed the tubers, let them air-dry for about 24 to 48 hours first, and keep them off bare concrete, which pulls moisture out of them.

You can divide now or wait until spring. Dividing in fall while the clump is fresh is easier on your hands and saves storage space. Waiting until spring makes the eyes easier to find. Either way, cure the tubers before they go into long storage.

Storage media

The job of the medium is to hold a little moisture around each tuber while still letting air move. Too dry and the tuber shrivels. Too wet and it rots. You want barely damp, not soggy.

Coarse vermiculite is a reliable choice. It holds moisture evenly and is less dusty than the fine horticultural grade. Dust-free wood shavings or wood chips, the kind sold as pet bedding, work about as well. Clean, slightly moist sand is another option.

Peat moss is harder to manage. Dry peat tends to make tubers shrivel, while moist peat tends to push them toward rot, so many growers skip it. Perlite does not absorb excess moisture the way vermiculite does, and the dust is hard on your lungs, so it is a poor fit for this job.

Pack the tubers in a cardboard box or a paper or plastic bag. Lay down an inch or two of medium, set the tubers so they are not touching, then cover with more medium and repeat the layers. Keeping tubers apart means one that rots is less likely to take its neighbors with it. Label as you go.

The plastic wrap method

If you want to skip loose medium altogether, wrap each tuber on its own. The American Dahlia Society describes rolling tubers in plastic wrap, and growers who use it report very low losses.

Tear off a sheet of plastic wrap about 20 inches long. Lay a single tuber near one end and roll it over once. Add another tuber, keeping it from touching the first, and roll again. You can bundle up to five tubers in one sheet this way. Fold the ends over and label the bundle.

Store the wrapped bundles at 40 to 45 degrees Fahrenheit in cardboard boxes or other containers. Reported losses to rot run on the order of 3 to 6 percent per year, with almost none lost to shriveling. One real advantage is that you do not have to check wrapped tubers through the winter the way you would with the vermiculite method.

If you dust tubers with sulfur first, use a very light coating. Too much sulfur turns the surface acidic and can kill the eyes of the tuber or hold back root growth.

Temperature and humidity targets

Cool and steady wins. Aim to hold storage between about 40 and 50 degrees Fahrenheit, above freezing but no warmer than the low 50s. Freezing turns a tuber to mush. Warmth wakes it up early and feeds the molds and fungi that cause rot.

Humidity around 70 percent keeps tubers from drying out without letting them sweat. A root cellar, an unheated basement, or an insulated garage that stays above freezing usually lands close to this range. A spare refrigerator can work too, though keep tubers away from ripening fruit, which gives off gases that shorten their dormancy.

Check the temperature with a cheap thermometer before you trust a space. A corner that feels cool to you can still swing below freezing on the coldest nights.

Monthly checks, rot, and shrivel

Look in on your tubers about once a month, or every few weeks if you can. Pull anything that has gone soft or moldy so it does not spread to the tubers around it.

Rot shows up as brown or rusty soft spots, often starting at the crown or at a cut. Healthy tuber flesh is firm and white inside. If only part of a tuber is affected, you can sometimes cut away the brown and save the rest, but throw out any tuber that has gone soft through the crown.

Shrivel is the opposite problem. A tuber that has lost too much moisture looks wrinkled and feels light and spongy. Light wrinkling is survivable. You can move shriveling tubers to a slightly more humid spot or lightly dampen the medium. A tuber that has dried hard all the way through will not grow, so let it go.

Both problems are easier to catch early. A clump checked monthly almost always stores better than one packed away and forgotten until April.