January 1999 Plant of the Month
Swamp Milkweed
(Asclepias incornata)

While a number of perennials grow best in the moist well-drained soil that every gardening book and magazine mentions, not everybody has the perfect soil.  I garden in heavy clay and have found Asclepias incornata to be an excellent choice for poorly drained soils.

Asclepias incornata is commonly known as swamp milkweed.  Swamp milkweed blooms for several weeks in early to mid summer.  It has pink to rosy red flat topped flower clusters on plants that get about four feet tall.  The plant makes a good cut flower and is long lasting in arrangements.  Like milkweeds in general, swamp milkweed has a thick milky white sap, and seeds with downy 'parachutes' that are dispersed by the wind.   Unlike many other milkweeds, swamp milkweed is a clump former and doesn't spread by aggressive roots.  Swamp milkweed is hardy to Zone 3 and grows over much of the eastern two thirds of the United States.  Even though it is often found in low, moist areas, it is quite happy in normal garden soil.  It is not a good plant for sandy, very well-drained soil unless given plenty of water.  If allowed to get too dry, it will drop it's lower leaves and look leggy. 

While the flower color of swamp milkweed can vary if grown from seed, several vegetatively propagated varieties have been selected in recent years.  'Ballerina' is pink; 'Ice Ballet' is white and 'Soulmate' is a rosy red selection.

By Rick Riemer, Dundee Nursery