Giant milkweed (Calotropis gigantea, syn. Asclepias gigantean) is a quaint shrub or small tree with plenty of character. These 6-foot plants display gnarled and twisted branches and often lean to one side as though blown by the wind. The flowers attract monarch butterflies which feed on the nectar. Giant milkweed produces seed pods that contain dozens of seeds. You can harvest a mature pod and plant the seeds or leave them to disperse naturally.
Giant milkweed flowers and produces seeds periodically throughout the year. The flowers bloom in clusters at the tips of the branches. They are followed by oval or kidney-shaped pods that measure between 2.7 and 4 inches long. The pods are green at first, turning brown and dry when mature.
When giant milkweed seed pods mature, they split open along the edge and invert, to release the seeds to the wind. Each seed has a tuft of white hairs that acts as a wind sail. The seeds take root wherever they make firm contact with soil. Competition from weeds and grasses and tall plants that shade them eliminate most of the seedlings, so that only a few survive.
You can start giant milkweed seeds indoors or out. They resist transplanting because of their long tap root that is easily damaged, so it’s best to sow the seeds in a permanent location. If you prefer to start them indoors, use peat pots so that you can transplant them later without disturbing the tap roots. Barely cover the seeds with soil. Germination can take up to three months, but usually takes much less. Plant giant milkweed outdoors in early spring or early fall.
Giant milkweed needs full sun and grows in almost any well-drained soils, including those that are poor in nutrients. The plants thrive in desert and seaside conditions and tolerate sandy or salty soil as well as salt spray and seaside winds. Giant milkweed has a high drought tolerance but it is more susceptible to insect infestations, particularly aphids, when under drought stress. It needs deep soil because of its long taproot. Giant milkweed is hardy in U.S. department of Agriculture plant hardiness zones 10 and 11.
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