Kalm's St John's wort

Questions about Kalm's St John's wort

Does Kalm's St John's wort need sun or shade?

Kalm's St John's wort grows in full sun (6 or more hours of direct sun a day).

It wants ordinary well-drained soil, of average fertility, and little watering once settled. Once settled in, it stands drought.

What zones does Kalm's St John's wort grow in?

USDA zones 4 to 7. It is hardy to zone 4, which means it survives winter nights down to about −20 °F (−29 °C).

Above zone 7 it struggles: the zones measure winter cold, but a plant's top zone usually means the summers are too hot or the winters too mild for it to rest.

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

When does Kalm's St John's wort 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 Kalm's St John's wort be planted?

2½ ft (75 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 3 ft (90 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 Kalm's St John's wort plants do I need?

At 2½ ft apart, set out in staggered rows:

• 2 to fill 10 square feet (about 1 m²)
• 5 for a single row 10 ft (3 m) long
• 6 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 one in one group.

Is Kalm's St John's wort poisonous to dogs and cats?

Yes: moderate toxicity to people, dogs, cats and horses. All parts are poisonous if eaten, and can make the skin of animals blister in sunlight.

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

Is there a pet-safe plant like Kalm's St John's wort?

These come closest to doing what Kalm's St John's wort does, and no toxicity is recorded for them:

• Shrubby cinquefoil 'Goldfinger': the same job in a bed and the same colour; 6 in wider, flowers early June to mid September.
• Rose 'Julia Child': the same job in a bed, the same size and the same colour; flowers mid June to early October, medium leaves, not fine.
• Leadplant: the same job in a bed and the same flowering time; 6 in shorter, 6 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 Kalm's St John's wort?

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 Kalm's St John's wort?

Kalm's St John's wort is over by early August. These start as it finishes and carry the same spot on, so it never goes flat:

• Lilyturf: from early August to mid September, 16 in tall, to stand in front of it and cover its fading stems.
• Sedum 'Autumn Joy': from mid August to mid October, 24 in tall, to stand in front of it and cover its fading stems.
• Little bluestem 'Standing Ovation': from early August to mid September, 3½ ft tall.

What does Kalm's St John's wort look like in winter?

Kalm's St John's wort holds some of its leaves into winter, more in a mild year or a sheltered spot, and they look tired by March. Cut the old ones off as new growth starts.

Is Kalm's St John's wort good for bees and butterflies?

Kalm's St John's wort is visited by bees and butterflies.

It is native to the United States and Canada.