Whorled milkweed

Questions about whorled milkweed

Does whorled milkweed need sun or shade?

Whorled milkweed grows in full sun (6 or more hours of direct sun a day) and part sun (4 to 6 hours of sun, including some afternoon sun).

It wants dry, sharply drained soil, on the lean side, with no feeding, and little watering once settled. Once settled in, it stands drought.

What zones does whorled milkweed grow in?

USDA zones 3 to 9. It is hardy to zone 3, which means it survives winter nights down to about −30 °F (−34 °C).

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does whorled milkweed flower in my zone?

In zone 5 it flowers late June to late August. As a summer flower it moves about half a week for every zone: earlier where it is warmer.

Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.

How far apart should whorled milkweed be planted?

16 in (40 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 18 in (45 cm), so a group knits into one patch.

It grows 24 in (60 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many whorled milkweed plants do I need?

At 16 in apart, set out in staggered rows:

• 7 to fill 10 square feet (about 1 m²)
• 8 for a single row 10 ft (3 m) long
• 21 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one at a time, threaded between sturdier plants.

In the bed above, the planner used two in two groups.

Is whorled milkweed poisonous to dogs and cats?

Yes: severe toxicity to people, dogs, cats and horses. All parts are poisonous if eaten, and it is the most toxic of the milkweeds to horses and other grazing animals. The sap can irritate skin and eyes.

Rated from NC State Extension and the ASPCA. Where references disagree, the more cautious rating is used.

Is there a pet-safe plant like whorled milkweed?

These come closest to doing what whorled milkweed does, and no toxicity is recorded for them:

• Mexican hat: the same job in a bed, the same size and the same flowering time; red or yellow, not white.
• Gaura 'Whirling Butterflies': the same job in a bed and the same colour; 12 in taller, flowers mid June to mid September.
• Rose campion: the same job in a bed and the same colour; 6 in taller, flowers early June to late July.

Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.

Do deer eat whorled milkweed?

Mostly not. NC State lists it as resistant to deer. No plant is proof against a hungry deer in a hard winter, but this one is low on the menu.

Will whorled milkweed spread?

It spreads sideways, by runners or roots; the risk of it taking over is moderate. Spreads slowly by underground stems into a loose colony. Pull stray shoots.

What flowers after whorled milkweed?

Whorled milkweed is over by late August. These start as it finishes and carry the same spot on, so it never goes flat:

• Prairie dropseed: from mid August to mid September, 2½ ft tall (a recorded partner).
• Garden chrysanthemum: from mid September to late October, 24 in tall.
• Japanese anemone: from mid August to early October, 3 ft tall.

What does whorled milkweed look like in winter?

Whorled milkweed dies down, but leave the stems standing: the seed heads stand through the winter, and songbirds eat the seed. Cut them down in early spring, before the new shoots come.

Is whorled milkweed good for bees and butterflies?

Whorled milkweed is visited by pollinators, bees, butterflies and songbirds.

It is a host plant: the caterpillars of monarch (at risk) feed on its leaves. A butterfly can only lay its eggs on its host plants, so these do more for it than any nectar flower.

It is native to the United States and Canada.