Frost Depth in Winter

Asked March 5, 2019, 3:56 PM EST

Hello, can you tell me how deeply frost/freeze penetrates the ground in the Kensington, MD (20895) area? Is it possible to plant tender bulbs (Agapanthus) below the depth of penetrating frost and have them survive over the winter? Thanks for your consideration of this question.

Montgomery County Maryland tender bulbs agapanthus plant care flowers: annuals and herbaceous perennials

5 Responses

According to the Maryland State Climatologist's Office, "The average frost penetration ranges from about five inches or less in extreme southern portions of Maryland to more than 18 inches on the Allegheny Plateau. In extremely cold winters, maximum frost penetration may be double the average depth."

In any case, Agapanthus is tender and cannot overwinter here.


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How do you suggest I manage the Agapanthus? Can they be lifted each year before frost? Can they be planted below the frost line and survive? My preference is not to place them in a pot. Thanks in advance for your suggestions.

How do you suggest I manage the Agapanthus? Can they be lifted each year before frost? Can they be planted below the frost line and survive? My preference is not to place them in a pot. Thanks in advance for your suggestions.

How do you suggest I manage the Agapanthus? Can they be lifted each year before frost? Can they be planted below the frost line and survive? My preference is not to place them in a pot. Thanks in advance for your suggestions.

We found that there is a cultivar of Agapanthus called 'Blue Yonder' that is supposed to be hardy down to Zone 5. You could try this type in the ground and cover it with a layer of mulch to provide added protection over the winter. Other varieties do best in warmer climates. You could lift and store the bulbs in the fall, but Agapanthus plants bloom best when the roots are crowded in a clump, so lifting and root disturbance may affect flowering.

ckc