9 steps for digging dahlia tubers and storing them through the Winter
Dahlias are not perennial where I live in Southern Quebec which is USDA plant hardiness zone 5. If your climate is zone 7 or warmer, you may consider leaving them in the soil. For me, it is either treating them like annual plants or digging them up for storage. I strongly think it is really worth the efforts doing the latter.
Labeling
While dahlias are still in bloom, be sure to label each plant with its proper name (do not rely on your memory, blooms are easier to identify the variety). It pays off to take notes of plant height and flower color and type on the reverse of the label, at least for one of a series. I also prepare one more label to be ready to use on the crates. My favorite labels are the self-tie loop lock vinyl plant tags handwritten on the spot with a permanent water-resistant sharpie pen. Position the label as close as possible to the ground. It is also the best time to review the health of each plant. The most concerning problem may be leaf gall, a bacterial disease, where mass of buds or short shoots are tightly packed together and fused at the base. These may appear beneath the soil or near the soil line at the base of the stems. These plants need to be discarded in the garbage and not to the compost pile. Tools and soil will need to be disinfected. If you suspect such a problem, search dahlia leaf gall on the web. If you do not see any problem, you are good to go. And then, when frost is announced, cut ALL flowers to waste none!
Cutting down
After frost has blackened the foliage, cut the stems to 4-6 inches to the ground, leaving the labels visible and well-tied. I prefer removing my dahlia/tomato cages at that moment. If you used another staking method, you may untie or move around the stakes. There is no rush to remove tubers as long as the soil is not frozen. The best is to wait for a dry day so the soil is not muddy and compact.
Lifting
Using a garden digging fork vertically, lift gently the soil in a 6-12 inches semi circle around the stem, avoiding damaging the tubers. The bigger the plant, the larger the circle. Compact soil demands a full circle. Do not pull on the stems until the soil is loose and tubers are easy to remove with both hands. Forage the soil to check of any leftover tubers.
Cleaning
Shake excess soil and remove with clean scissors any damaged or rotten tubers at first glance. Some clumps will divide themselves but do not separate the tubers by pulling on them. I use plastic crates to store temporarily each variety, dividing the crate if multiple varieties are placed in the same crate.
Hair cutting
With clean scissors, remove all hair-like roots. Also prune any snake-like, pencil-size tubers not swollen in their middle. Cut the stem to an inch or less without damaging the eyes that could be at the base. Remember, soft tissues rot more easily and the mold can then infect good tubers. The original tuber may be damaged or rotten, be sure to remove it if it is so. Try to disinfect your tools with isopropyl alcohol or diluted tsps followed by a water rince before handling each new plant.
Drying
If the tubers are wet, let them dry long enough and check on them for early signs of molding. Tubers can be stored with some soil or washed though this will necessite a longer drying period.
Storing versus dividing
Tubers can be stored in clumps or be divided at this stage. There is no right or wrong. I have done both. Division will be adressed in another blog article.
Protecting from fungal disease
Use a powder or liquid fungicide to protect the cut tips and by association the tubers. I use Safers’ Sulphur Dust, but ask your garden center to check availability of other products in your area.
Storing media and containers
Storing is the most important step. Ventilation, cool temperature (40-50 degrees F) and dry air (with light humidity, but no dampness) are the most important factors. The favored media are vermiculite, peat moss, perlite, sand or wood chips. Vermiculite is ideal as it is non organic but more expensive. I use very dry wood chips because I get a large bag at low costs at a nearby coop store for horse owners. I space the tubers in layers of wood chips in flower bulb (rectangular) or milk (square) plastic crates. These are stackable and offer ventilation. I line and top them with a sheet of newspaper. I label each crate with its content and be sure each layer is labeled too, or better individual tubers. I spot check the tubers few times over the course of the Winter. If some tubers seem to develop mould, try to see why this is happening, reviewing storage conditions such as ventilation and humidity . Do not panic and throw everything in the compost pile. There are some steps we will do in the Spring to save some of the tubers as long as they are not too soft.
