I’m enamored of milkweeds. Anyone who’s visited my northern New York garden knows that. Their elegant flowers, their silk-borne seeds, their scents, their value as butterfly fodder all enchant me.
The USDA PLANTS database (http://plants.usda.gov) lists 76 Asclepias species native or introduced to the United States. Of these, I have grown (or tried to grow) around 30, and I currently have 15 established in the garden. Of those, there are probably four species that I wholeheartedly recommend as garden plants. I wouldn’t be without the others, and I plan to add more—but they’re not for every gardener.
FOUR MUST-HAVE MILKWEEDS
Let’s start with the clear winners. The species most familiar to gardeners is probably Asclepias tuberosa, or butterfly weed, that glorious early- to midsummer bloomer with flowers typically mid-orange but ranging from yellow through gold and orange to a deep red-orange. Sited in the full sun and sharply drained soil that it prefers, it produces masses of crowded flat-topped umbels of brilliant small flowers atop two- to three-foot stems clad in attractive lanceolate leaves. This species seems to be quite salt-tolerant; most of my plants are right by the road, where the snow plows anoint them annually with tons of salty snow (I live in Lake Ontario’s snow belt, with an annual average snowfall of 12 feet). As their common name implies, they are delightfully attractive to butterflies and other insect pollinators, as are most milkweeds.
A less commonly grown but also spectacular species is A. purpurascens, or purple milkweed. This larger plant resembles its close relative common milkweed (A. syriacus) in form but not in temperament. A gentle spreader in the garden, A. purpurascens has dense round umbels of brilliant red-purple flowers, arrayed along and at the top of three-and-a-half- to four-foot stems in early summer. Happy with sun to part shade and moderate moisture, it looks particularly good planted next to a mass of white-flowered Parthenium integrifolium, the magnificent and sadly underused wild quinine, or American feverfew.
If your garden has more shade than sun, you may want to grow A. exaltata, the poke milkweed. As the specific name implies, this is a big one, up to five feet tall, and strictly a clump-former. In midsummer it displays loose umbels of large, dramatically shaped flowers, each flower arching outward on a long pedicel. They look like pale pink, white and green fireworks against the deep green leaves.
The western A. asperula, or antelope horns, surprised me with its resounding success. I grow this one in the rock garden to ensure full sun and excellent drainage, and here it sprawls over the rocks, the end of each foot-long stem adorned in early summer with a perfectly astonishing round umbel of five-sided cupped green and purple flowers, somewhat resembling a geodesic dome.
PROCEED WITH CARE
With the above four species, you are safe: They will not take over your garden. We now venture onto thinner ice.
The large milkweeds, adapted to heavy competition in grasslands, are both splendid and dangerous plants. The eastern common milkweed, A. syriacus, is magnificent in the wild. Its distinctive musky scent recalls for me distant childhood summers, and as an adult I’ve enjoyed studying its natural variation. Flower colors range from a fairly unappealing pale liver pink through deep dusky reddish purple; stems may hold just a few umbels or, in the case of one I begged from a neighbor and put in my garden (yes, I did), may have axillary umbels all along the stem from top to bottom. It runs like crazy; it is not a plant for the small or orderly garden. But it’s beautiful.
From farther west comes A. speciosa, with flowers among the most beautiful in the genus (speciosa means beautiful, handsome, or imposing). It runs enthusiastically in garden conditions, so I keep it in check by planting it by the road, where it meets asphalt on one side and the lawnmower on the other if it strays too far. I’m about to try—and am prepared to adore—A. speciosa ‘Davis’, a selection found near Davis, California. Unlike the typical smooth-leaved A. speciosa, this one is woolly all over, a typical adaptation for desert plants. I don’t know whether it will prove to be as hardy as the more eastern type, but experimentation is half the fun of gardening!
Another broad-leaved westerner, A. latifolia, has been charmingly persistent and well behaved in my rock garden. Its handsome foliage makes up for its total failure to flower for me. This is a short plant, one to one-and-a-half feet tall in my garden, but its glossy silvered leaves, reminiscent of eucalyptus, are up to six inches long.
Departing now from the coarse-leaved milkweeds, we come to those with fine foliage and pale pinky white to green flowers. Perhaps the most enchanting flowers in this group belong to A. hirtella, a Central States native. Though the plant can be ungainly in gardens (I recommend staking it) the inflorescences, crowded along the stem, are wonderful round umbels of up to 100 little peglike purple-tipped green flowers. This plant emerges late and grows slowly here—no signs yet of thuggery. Other narrow-leaved species include the eastern A. verticillata and its western counterpart, A. subverticillata, both with umbels of tiny greenish white flowers along the stem, and the petite, charming and rampant A. pumila, a Plains native that runs all over in the rock garden but ranks awfully high for cuteness.
There are many more milkweeds, some I grow, some I can’t, some I don’t want to. Be brave, and give Asclepias a try.