Dahlias put on a colorful, bright summer show, but as cooler weather arrives, their presence begins to fade.
While dahlias are grown as perennials in zones 8 and higher, in lower zones they are treated as annuals. But, if you dig dahlia tubers (often called bulbs) up at the right time, you can replant them in the spring and enjoy a repeat show.
Here’s the attention you need to give dahlias in the fall and tips for perfect summer blooms.
Let Them Freeze First
For most plants, the first frost is a death knell. For dahlias, it is a way for dahlia growth to cease so the bulbs can store food supplies and set eyes for new growth next spring.
After the first hard frost when the foliage has blackened and withered, cut each plant back to around four inches above the ground. Leave the tubers in the ground for one week before returning to dig them up.
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Dig Up Dahlia Bulbs
Once the bulbs have hardened off, move about 12 inches away from the stem and begin digging up each root ball with a garden spade or fork.
- Carefully clean off the excess soil and remove the tubers. Work slowly so you do not cut or damage the tuber.
- This is a good time to label each tuber with a tag with the color and variety of the dahlia.
- The tubers should be placed in a sheltered, well-ventilated, dark location (garage or tool shed) and allowed to air-dry for at least a week before moving them to their winter storage spot.
Divide Dahlia Bulbs
Once the dahlia bulbs have air-dried for a week, it’s time to inspect them and make any divisions before it’s time to plant next spring.
- Inspect the bulbs. Check the bulbs for any rotten or damaged areas.
- Trim the root ball of bulbs. Use clean, sharp garden shears to trim away tubers or roots that are soft, cut, or damaged. Trim the roots so they are just a few inches long.
- Locate the crown of the plant. The crown or center of the dahlia is located at the base of the stem. The eyes of the tubers are located there and that’s where new growth will emerge next spring. Each division must have a piece of the crown with at least one or two eyes.
- Divide the bulbs. Use a sharp paring knife to cut each tuber away from the main stalk making sure each one has a portion of the underground stem with an eye.
- Remove the mother tuber. The mother tuber is the one that produced the plant that just died. The tuber will be darker and more shriveled or wrinkled than the others. Since it has already produced a plant, it does not have the energy stores to repeat the process.
- Sterilize your knife. Before you move to another dahlia clump, sterilize your knife with some rubbing alcohol to help prevent the spread of disease between clumps.
- Allow the fresh cuts to cure. The freshly cut surfaces should dry for 24 to 48 hours before storing the bulbs.
Store Dahlia Bulbs the Right Way
The key to successful storage is to keep the dahlia clumps or bulbs in a dark area between 35 and 50 degrees F. Some humidity is okay but it should not be constantly damp.
- Use a newspaper and a cardboard box. Newspaper and cardboard allow some air circulation. Layer newspapers and tubers in the box and close it to prevent light penetration. You can also wrap each one in newspaper and store them in a paper bag.
- Store in net bags. If you have a cool, dark area, hang tubers in net bags for storage.
- Refrigerate: Individual tubers can be placed in plastic bags with vermiculate and stored in a refrigerator.
- Use vermiculite or sand. Tubers can be layered in a cardboard or wooden box with vermiculite or sand. Never use potting or garden soil. Sand is not recommended if the storage area is overly damp.
- Check the tubers. Tubers should be checked once a month during winter storage. Discard any tubers that are soft and rotting. If the tubers feel overly dry, lightly mist them with plain water to increase humidity.