When to Plant - Some Seeds Must Wait!

Q. over three weeks ago I planted several vegetable seeds: Onion,
carrot, radish, pumpkin, cucumber, squash, sunflower, corn and green
beans. I planted them all according to the instructions, (I think).
The only thing that has sprouted great are the radishes. The
sunflowers have few sprouts, but they look really weak. Do you have
any advice on how long I should wait to replant or what I can do
differently?

A. On warm days in early spring we are often enticed to plant things
that require warm temperatures to grow. Then we are sorely
disappointed when cold temperatures return and the seeds rot in the
cold ground or die trying to grow in the too-cold environment.

Your onion, carrot, and radish seeds may be able to live in early
spring temperatures, but onion and carrot will be slow to germinate
and grow, so don't give up on them just yet.

As for all the others you mentioned, they must have warm soil
conditions to germinate and grow, and any frost would kill them if
they did come up.

Just wait until after all danger of frost is past before planting. Alternatively, you can plant them in a greenhouse
or under grow-lights 3 or 4 weeks earlier. Remember to give them maximum light immediately upon emergence, and plant in 6-paks or pots, to minimize transplanting shock, because everything you named does very poorly as a bare-root transplant.