Yellow flag iris

Questions about yellow flag iris

Does yellow flag iris need sun or shade?

Yellow flag iris 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 yellow flag iris grow in?

USDA zones 4 to 9. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).

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

When does yellow flag iris 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 yellow flag iris be planted?

24 in (60 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 2½ ft (75 cm), so a group knits into one patch.

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 yellow flag iris 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 one at a time, repeated along the bed at intervals; a slender one reads better as a clump of three.

Is yellow flag iris 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.

What can I plant instead of yellow flag iris?

Yellow flag iris is listed as invasive in parts of North America, so the planner never uses it. These do the most similar job, and are native:

• Carolina lupine: the same job in a bed, the same size, the same flowering time and the same colour; wants average soil.
• Lupine: the same job in a bed, the same flowering time and the same colour; 8 in shorter, 6 in narrower.
• Cardinal flower: the same job in a bed; 8 in shorter, 10 in narrower.

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

Do deer eat yellow flag iris?

They may. NC State does not list it as resistant to deer or rabbits. Where they visit, protect it, or plant it among ones they avoid.

Will yellow flag iris spread?

It spreads sideways, by runners or roots; the risk of it taking over is high. Spreads by rhizomes and water-borne seed, and forms dense stands that crowd out native wetland plants. Listed as invasive and banned from sale in many states and provinces.

It is listed as invasive in parts of North America, and the planner never chooses it.

What flowers after yellow flag iris?

Yellow flag iris 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).
• Bee balm: from early July to early August, 3 ft tall, to stand in front of it and cover its fading stems.
• Purple coneflower: from late June to early September, 3 ft tall, to stand in front of it and cover its fading stems.

What does yellow flag iris look like in winter?

Yellow flag iris 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.