Sweet Cicely

Easy to grow and will self seed all over the place once established. Needs a period of cold to force it to start germinating, so summer sown seed may not germinate until the following spring.

Doesn't stop you haveing to use sugar, just encourages you to use less. Having said that it's just as easy to educate your pallet to accept less sugar, which can easily be halved in most recipes without the need to resort to herbs. Anyway, I like the smell of sweet cicely and it's worth growing for that alone.

I grow this and use a couple of leaves when cooking fruit like rhubarb to reduce the amount of sugar you need.  It does work 

You can eat the seeds as well when they are fresh and green.  They taste a bit like those liquorice comfit sweets.  I munch my way round the watering when they are ready