Maxim wrote:

I was wondering, when would it be suitable to start planting things like
broad beans, corn, french beans, sunflowers and other large plants?

Early broad beans (e.g. Aquadulce Claudia or The Sutton) can be sown as
soon as you like, better still last autumn. Under cover ideally, but
they're pretty tough.

Sweetcorn and French beans are tender, so not until the last frost,
though you can push things a little bit by starting them off inside.
But starting too early is a waste of time.

The maximum temperature in my area is only around 14c during the day.

Minimum night time temperature is also important (more important?), and
will likely be negative at the moment.

Peter