The soil must be depleted of vital nutrients for carrots. Plant your carrots in a different location and try a different crop in said location. Go to 'Google', type in "Crop Rotation" and read a couple articles as to why it's necessary to give the ground a 'rest' every few years.

I think I would leave the area sweet pea free for a couple of years. there could be some bacteria/pest that is preventing them from thriving. they don't mind poor nutrient soil as they have root nodules containing a bacterium that fixes nitrogen.

cant think what else would be the cause.

When you say 'not thriving' do you mean the stems aren't growing well? Or the flower buds are dropping off?
We've had ridiculously changeable weather recently that might cause bud drop but hopefully it'll even out in time

Sorry I meant to say Sweat Peas.

Lol Bathgate... no sweat...

Chega you might like to try planting some brassicas in the spot next year instead. They will enjoy the nitrogen the sweet peas have produced for you!

Thank you for your help, might be right about soil depletion and rotating, they had been grown there for several years, they are not even taking off about 8"high poor leaves looking sickly, some planted out in a large container looking good 3ft high now flowering so it can't be actual plants got to be a soil issue?