Look to ensure a distance
11.7 inches (30.0 cm) between Heidi Eidelweiss seeds when sowing to make sure your seedlings have enough space.
By our calculations, you should look at sowing Heidi Eidelweiss about 42 days before your last frost date.
As Heidi Eidelweiss is hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.