sweet peas

In zone 5 when can sweet pea seeds be put into the ground

Doug says that sweet peas can (and should be) sown directly into cool soils. Generally, you're looking at mid-April or whenever you can put your bare wrist on the soil and not freeze your hand off your arm.

If unsure, you can plant them in jiffy-pellets in a cool room and then transplant outdoors when the plant has 4-6 leaves.

I'd be planting outdoors.