Dahlia bulbs, commonly called tubers, are often lifted in order to store them for the winter, protecting them from the harsh weather. Any hard freeze will ultimately kill the delicate dahlia bulbs and render them unable to grow. Lifting will help to save the bulbs for the following growing season. The high cost of the bulbs makes lifting them, storing and replanting an economical idea that can provide several years of enjoyment from one bulb.
Lift the Dahlia
Lift dahlia bulbs after the first frost begins to blacken the green foliage. The frost will place the bulbs into a dormant state. Prepare to lift the bulbs within 4 to 7 days after the frost blackens the foliage. Cut foliage down to 4 to 6 inches. Rake away any mulch from around the plant. Take a handheld trowel and begin to dig 1 foot out from the plant in a circle. A shovel can be utilized instead of a handheld trowel, but be careful not to cut into the plant with the large shovel by mistake. Work your way under the plant and then gently lift it out. Never pick up the plant by the remaining stem or you will break the delicate stem. Pick up the entire root ball with your hands.
Remove the Soil
Place the root ball by a garden hose. Turn the garden hose on gently and wash the soil away from the bulbs. Be gentle and do not use a large forceful spray. Work the dirt away from roots and bulbs with your fingers. Be very careful to not remove any of the skin on the bulbs, which will damage the plant and render it unable to grow the following season. Many do not utilize water to wash the soil from the dahlia bulbs because they believe it can make fungus grow over the winter. Simply remove the soil using hands without utilizing water.
Dust the Bulbs
Pat bulbs and roots dry with a towel if you have rinsed with water. If you have simply removed the dirt, then you will not need to dry the bulbs. Apply a light dusting of sulphur powder to the bulbs and roots to prevent fungus. Sulphur powders can be purchased at any garden supply store.
Store the Bulbs
Place the dahlia bulbs into a brown paper bag. Pour 4 cups of sawdust or coarse vermiculite into the paper bag with the bulbs. Crinkle the top of the paper bag closed. Label each paper bag with a marker for identification next spring.
Place the bags into a container such as a rubber box container with a lid or a box that you can close off to allow no light into. Place into a storage area where the temperature can be maintained between 45 and 50 degrees F. An insulated garage, storage shed or potting shed will work if the temperature can be maintained. Check the bulbs once a month through winter to make sure they are not drying out. If the bulbs look shriveled, spritz them with a light spray of water so they do not dry out.
Replanting in Spring
In the spring, when all danger of frost has passed, decide what location to replant the bulbs in. Dahlias require 8 hours of sun per day to thrive. Dig a hole that is one and a half times the size of the bulbs and roots. Create a mixture of 50 percent peat moss and 50 percent garden soil.
Remove the box with the bulbs from storage and gently lift the bulbs from their bags. Dust each bulb and roots again with a sulfur fungicide. Gently place the bulbs into the holes in the garden. Firmly place the peat moss and garden soil around the roots. Let the top part of the remaining foliage peek out of the soil. Place 3 inches of mulch around the replanted dahlia bulbs. Use peat moss, sawdust, bark chips or recycled plastic mulch. Water thoroughly after replanting. Keep dahlias moist for optimum growth.
Apply a 5-10-10 general purpose plant food fertilizer after 30 days. Sprinkle 1/2 cup of fertilizer around the base of the dahlia and water thoroughly.