FrostCal

When to Plant Cosmos in Pennsylvania

In a typical Pennsylvania location, start seeds indoors Mar 23 – Mar 30, then sow outdoors Apr 27 – May 11, then transplant outdoors Apr 27 – May 4. Across the state, the outdoor planting window starts as early as Apr 6 in Philadelphia and as late as May 22 in Hermitage.

Method Direct sow
Days to maturity 60–90 days

Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early.

Cosmos Planting Dates by City

CityStart indoorsDirect sowTransplant
PhiladelphiaMar 2 – Mar 9Apr 6 – Apr 20Apr 6 – Apr 13
PittsburghMar 27 – Apr 3May 1 – May 15May 1 – May 8
AllentownMar 23 – Mar 30Apr 27 – May 11Apr 27 – May 4
ErieMar 29 – Apr 5May 3 – May 17May 3 – May 10
ReadingMar 17 – Mar 24Apr 21 – May 5Apr 21 – Apr 28
ScrantonMar 26 – Apr 2Apr 30 – May 14Apr 30 – May 7
BethlehemMar 23 – Mar 30Apr 27 – May 11Apr 27 – May 4
BensalemMar 24 – Mar 31Apr 28 – May 12Apr 28 – May 5
LancasterMar 22 – Mar 29Apr 26 – May 10Apr 26 – May 3
AbingtonMar 14 – Mar 21Apr 18 – May 2Apr 18 – Apr 25
LevittownMar 24 – Mar 31Apr 28 – May 12Apr 28 – May 5
HavertownMar 2 – Mar 9Apr 6 – Apr 20Apr 6 – Apr 13
HarrisburgMar 18 – Mar 25Apr 22 – May 6Apr 22 – Apr 29
AltoonaMar 28 – Apr 4May 2 – May 16May 2 – May 9
YorkMar 29 – Apr 5May 3 – May 17May 3 – May 10
State CollegeMar 23 – Mar 30Apr 27 – May 11Apr 27 – May 4
Wilkes-BarreMar 26 – Apr 2Apr 30 – May 14Apr 30 – May 7
NorristownMar 11 – Mar 18Apr 15 – Apr 29Apr 15 – Apr 22
ChesterMar 2 – Mar 9Apr 6 – Apr 20Apr 6 – Apr 13
Mount LebanonMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
Bethel ParkMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2
WayneMar 11 – Mar 18Apr 15 – Apr 29Apr 15 – Apr 22
RadnorMar 11 – Mar 18Apr 15 – Apr 29Apr 15 – Apr 22
WilliamsportMar 28 – Apr 4May 2 – May 16May 2 – May 9
MonroevilleMar 25 – Apr 1Apr 29 – May 13Apr 29 – May 6
Cranberry TownshipMar 11 – Mar 18Apr 15 – Apr 29Apr 15 – Apr 22
Drexel HillMar 5 – Mar 12Apr 9 – Apr 23Apr 9 – Apr 16
PlumMar 19 – Mar 26Apr 23 – May 7Apr 23 – Apr 30
Back MountainMar 26 – Apr 2Apr 30 – May 14Apr 30 – May 7
EastonMar 21 – Mar 28Apr 25 – May 9Apr 25 – May 2

Showing the 30 most populous of 121 Pennsylvania cities. Dates are estimates from each city's NOAA frost normals and university extension timing guidelines. See all Pennsylvania cities.

Frequently Asked Questions

When should I plant cosmos in Pennsylvania?

In a typical Pennsylvania location, start seeds indoors Mar 23 – Mar 30, then sow outdoors Apr 27 – May 11, then transplant outdoors Apr 27 – May 4. Across the state, the outdoor planting window starts as early as Apr 6 in Philadelphia and as late as May 22 in Hermitage.

When is the last frost in Pennsylvania?

The average last spring frost in Pennsylvania ranges from March 30 in Philadelphia to May 15 in Hermitage, based on NOAA 1991–2020 climate normals.

How long do cosmos take to grow?

Cosmos typically take 60–90 days from planting to harvest. Easy from direct seed 1-3 weeks after last frost; can also start indoors 3-4 weeks early.

Other Crops in Pennsylvania

When to plant cosmos in other states

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