Swamp milkweed

Questions about swamp milkweed

Does swamp milkweed need sun or shade?

Swamp 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 soil that stays evenly moist, of average fertility, and plenty of water. It copes with soil that stays wet.

What zones does swamp 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 swamp milkweed flower in my zone?

In zone 5 it flowers early July to early 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 swamp milkweed be planted?

24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is about its full width, so each plant keeps its own outline.

It grows 4 ft (120 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many swamp milkweed plants do I need?

At 24 in apart, set out in staggered rows:

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

In a mixed border, plant it as a group of three or five, with a second group further along in the other number.

In the bed above, the planner used three in one group.

Is swamp milkweed poisonous to dogs and cats?

Yes: moderate toxicity to people, dogs, cats and horses. All parts are poisonous if eaten. 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 swamp milkweed?

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

• Garden phlox 'Jeana': the same job in a bed, the same size and the same colour; flowers mid July to mid September.
• Bee balm 'Jacob Cline': the same job in a bed, the same size and the same flowering time; red, not pink.
• Joe Pye weed 'Little Joe': the same job in a bed, the same size and the same colour; flowers late July to early September, bold leaves, not medium.

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

Do deer eat swamp milkweed?

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

What flowers after swamp milkweed?

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

• New England aster: from early September to mid October, 4 ft tall (a recorded partner).
• Japanese anemone: from mid August to early October, 3 ft tall, to stand in front of it and cover its fading stems.
• Lilyturf: from early August to mid September, 16 in tall, to stand in front of it and cover its fading stems.

What does swamp milkweed look like in winter?

Swamp milkweed dies down to the ground and there is nothing to see until spring. The old stems can be cut in autumn, or left until spring as shelter for overwintering insects.

Is swamp milkweed good for bees and butterflies?

Swamp milkweed is visited by pollinators, butterflies and beneficial insects.

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.