Lemon balm · Philadelphia, Pennsylvania, United States
When to plant lemon balm in Philadelphia
Main outdoor window
31 Mar - 21 Apr
The window this page is built around.
Timed from last spring frost
14 April
In Philadelphia, on your chosen risk.
Ready to pick
1 May - 31 Oct
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.
Start indoors
17 Feb - 10 Mar
Eight weeks before your last frost, under cover or on a windowsill.
Sow direct
31 Mar - 21 Apr
Two weeks before your last frost.
Plant out
28 Apr - 19 May
Two weeks after your last frost.
Harvest
1 May - 31 Oct
Lemon balm through the year
Against the frost risk in Philadelphia
Why these dates
Extremely hardy, to about -25C. Dies to the ground and returns reliably.
Seed packets and extension guides express timing as weeks either side of the last spring frost, because that is the only reference point that travels. Lemon balm are timed from 8 weeks before that frost for an indoor start, with planting out 2 weeks after it, and this page simply resolves those offsets against the frost date computed for Philadelphia.
Hardiness is not the obstacle here. Philadelphia is zone 7a, comfortably inside the range this crop is rated for, so an established plant should come through an average winter without protection.
Do not expect a crop in the first year. A plant set out now should give its first worthwhile pick around year 1, and will then produce every year after that, which is what makes the planting decision worth getting right the first time.
Growing lemon balm in Philadelphia
When should I plant lemon balm in Philadelphia?
Aim for 31 Mar - 21 Apr in an average year. If you would rather not gamble on the weather, wait until 9-30 Apr - by then frost has finished in nine years out of ten.
When will lemon balm be ready to harvest in Philadelphia?
Expect to start picking around 1 May - 31 Oct, based on 70 to 90 days to maturity from the planting date calculated for this location.
How much frost will lemon balm tolerate?
Extremely hardy, to about -25C. Dies to the ground and returns reliably.