Calla lily · Philadelphia, Pennsylvania, United States
When to sow calla lilies in Philadelphia
Main outdoor window
21 Apr - 19 May
The window this page is built around.
Timed from last spring frost
14 April
In Philadelphia, on your chosen risk.
Ready to pick
1 Jun - 31 Aug
If you plant at the start of the window.
The average last frost. Half of all years are later than this.
Step by step in Philadelphia
Each window is a range, not a single day. Earlier in the range buys you a longer season; later in it buys you a safer one.
Plant the rhizomes
21 Apr - 19 May
After the last frost, once the soil has warmed. This crop is never fully dormant, so it cannot be planted bare-root in winter.
In flower
1 Jun - 31 Aug
Calla lilies through the year
Against the frost risk in Philadelphia
Why these dates
Plant a week after the last frost, 8cm deep, and water generously - this is one of the few plants here that cannot be overwatered in summer. In zone 8 and warmer it can be left in the ground and treated as an ordinary perennial.
Hardy to about -5C with a mulch, and the white-flowered species is the toughest of the group; the coloured hybrids are appreciably more tender. Below zone 8 lift and store the rhizomes, or overwinter the pot dry under cover.
Calla lilies are planted once and then left in place, so there is no sowing offset to resolve. Nor is there a dormant season to plant into: this crop keeps its leaves and keeps growing through the winter, which is exactly why cold damages it. The window on this page therefore waits until the last frost in Philadelphia has passed and the soil has begun to warm, giving the roots the longest possible run before the cold returns.
Philadelphia sits in zone 7a, which is colder than this crop is rated for, so it will need winter protection or a container that can be moved under cover. The dates below still describe the right time of year; the open question is survival rather than timing.
Nearby
Calla lilies in places close by
Also in Philadelphia
Other flowers to time
Growing calla lilies in Philadelphia
When should I plant calla lilies in Philadelphia?
Aim for 21 Apr - 19 May in an average year. If you would rather not gamble on the weather, wait until 30 Apr - 28 May - by then frost has finished in nine years out of ten.
When will calla lilies be ready to harvest in Philadelphia?
Expect to start picking around 1 Jun - 31 Aug, based on 100 to 130 days to maturity from the planting date calculated for this location.
How much frost will calla lilies tolerate?
Hardy to about -5C with a mulch, and the white-flowered species is the toughest of the group; the coloured hybrids are appreciably more tender. Below zone 8 lift and store the rhizomes, or overwinter the pot dry under cover.