Southern blue flag

Questions about southern blue flag

Does southern blue flag need sun or shade?

Southern blue flag 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 moist to wet soil, rich in organic matter, and plenty of water. It copes with soil that stays wet.

What zones does southern blue flag grow in?

USDA zones 5 to 9. It is hardy to zone 5, which means it survives winter nights down to about −10 °F (−23 °C).

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

When does southern blue flag flower in my zone?

In zone 5 it flowers late May to late June. As a spring flower it moves about a week for every zone: earlier where it is warmer, later where it is colder.

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 southern blue flag be planted?

20 in (50 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 24 in (60 cm), so a group knits into one patch.

It grows 2½ ft (80 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many southern blue flag plants do I need?

At 20 in apart, set out in staggered rows:

• 4 to fill 10 square feet (about 1 m²)
• 7 for a single row 10 ft (3 m) long
• 14 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 southern blue flag poisonous to dogs and cats?

Yes: mild toxicity to people, dogs, cats and horses. The underground stems (rhizomes) and leaves can cause drooling and stomach upset if eaten.

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

Is there a pet-safe plant like southern blue flag?

These come closest to doing what southern blue flag does, and no toxicity is recorded for them:

• Columbine meadow rue: the same job in a bed, the same size and the same flowering time; lavender, pink or white, not blue, fine leaves, not bold.
• Globeflower: the same job in a bed, the same size and the same flowering time; yellow or orange, not blue, medium leaves, not bold.
• Golden Alexanders: the same job in a bed, the same size and the same flowering time; yellow, not blue, medium leaves, not bold.

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

Do deer eat southern blue flag?

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.

What flowers after southern blue flag?

Southern blue flag is over by late June. These start as it finishes and carry the same spot on, so it never goes flat:

• Swamp milkweed: from early July to early August, 4 ft tall (a recorded partner).
• Black-eyed Susan: from mid July to mid September, 24 in tall, to stand in front of it and cover its fading stems.
• Yarrow: from mid June to late August, 24 in tall, to stand in front of it and cover its fading stems.

What does southern blue flag look like in winter?

Southern blue flag 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.