Yard and Garden: Over-winter Tender Perennials

AMES, Iowa — Perennials such as tuberous begonias, gladioli, cannas and dahlias are an integral part of many home landscapes. They put on excellent displays of color until a killing frost. Unfortunately, they will not survive Iowa's harsh winter weather outdoors and must be dug in the fall and stored indoors through the winter months. Horticulturists with Iowa State University Extension and Outreach offer cultural and winter storage requirements for several commonly grown tender perennials. To have additional questions answered, contact the Hortline at 515-294-3108 or email hortline@iastate.edu.

How do I over-winter dahlias? 

Cut back the plants to within 2 to 4 inches of the ground within three or four days of a killing frost. After cutting back the plants, leave the dahlias in the ground for an additional six or seven days to “cure.” Then carefully dig up the dahlias with a spade or shovel. Gently shake off the soil, then cut the stems back to within 1 inch of the crown. (The dahlia crown is located at the base of the stems where the tuberous roots are attached.) Carefully wash the dahlia clumps to remove any remaining soil. Allow the dahlias to dry for 24 hours.

When the dahlias are dry, place a layer of vermiculite, peat moss or wood shavings in the bottom of a cardboard box. Place the dahlia clumps upside down on the storage medium and then cover the dahlias with additional vermiculite, peat moss or wood shavings. Repeat the layering procedure until all the dahlias have been placed in the box or the box is full. Store the dahlias in a cool (40 to 50 degree Fahrenheit), dry location. 

How do I over-winter gladiolus bulbs? 

Carefully dig up the plants with a spade in late summer/early fall. Gently shake off the soil from the bulb-like corms. Then cut off the foliage 1 to 2 inches above the corms. Dry the corms for two to three weeks in a warm, dry, well-ventilated location. When thoroughly dry, remove and discard the old dried up mother corms located at the base of the new corms. Remove the tiny corms (cormels) found around the base of the new corms. Save the small corms for propagation purposes or discard them. Place the corms in mesh bags or old nylon stockings and hang in a cool, dry, well-ventilated location. Storage temperatures should be 35 to 45 degrees Fahrenheit. 

How do I over-winter cannas indoors? 

Cut the plants back to within 4 to 6 inches of the ground a few days after a hard, killing frost. Then carefully dig up the canna clumps with a spade or garden fork. Leave a small amount of soil around the cannas. Allow them to dry for several hours.

Afterwards, place the cannas in large boxes, wire crates or in mesh bags. Store the cannas in a cool (40 to 50 degree Fahrenheit), dry location.

How do I over-winter tuberous begonias? 

Carefully dig up the tuberous begonias within a few days of a killing frost. Leave a small amount of soil around each tuber. Cut off the stems about 1 inch above the tubers. Place the tubers in a cool, dry area to cure for two to three weeks. After curing, shake off the remaining soil. Place a layer of peat moss, vermiculite or sawdust in a small cardboard box. Lay the tubers on the storage medium, then cover the tubers with additional peat, vermiculite or sawdust.  Store the tubers in an area with a temperature of 40 to 50 degrees Fahrenheit. 

How do I over-winter caladiums indoors? 

Carefully dig up the caladiums when the foliage begins to yellow with the onset of cool weather or wait until after the first frost. After digging, place the plants in a cool, dry location for one to two weeks to cure. After curing, cut off the dry foliage. Place a layer of peat moss, vermiculite or sawdust in a small cardboard box. Lay the tubers on the storage medium, then cover with additional peat, vermiculite or sawdust. Store the caladiums in a cool (60 to 65 degree Fahrenheit), dry location. 

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