Japanese iris

Questions about Japanese iris

Does Japanese iris need sun or shade?

Japanese 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 Japanese 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 Japanese iris flower in my zone?

In zone 5 it flowers late June to mid July. 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 Japanese iris be planted?

18 in (45 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 20 in (50 cm), so a group knits into one patch.

It grows 3 ft (90 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many Japanese iris plants do I need?

At 18 in apart, set out in staggered rows:

• 5 to fill 10 square feet (about 1 m²)
• 7 for a single row 10 ft (3 m) long
• 17 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.

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

Is Japanese 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.

Is there a pet-safe plant like Japanese iris?

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

• Meadow sage 'Caradonna': the same job in a bed and the same colour; 12 in shorter, flowers late May to mid July.
• Maltese cross: the same job in a bed, the same size and the same flowering time; belongs at the back, not in the middle, red, not purple.

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

Do deer eat Japanese iris?

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 Japanese iris?

Japanese iris is over by mid July. These start as it finishes and carry the same spot on, so it never goes flat:

• Cardinal flower: from late July to mid September, 3½ 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.
• Bee balm: from early July to early August, 3 ft tall.

What does Japanese iris look like in winter?

Japanese 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.