By Pdb
Lancashire,
United Kingdom 
I have planted my sweet peas in the same spot for the last 3 years. However this year they haven't done very well. Could it be because they have been in same soil. I do add a handful of new compost with each plant.
20 Jul, 2017
Answers
my sweet peas have been in the same run for years, and I have no problems. This year I even have some with 5,6 and 7 blooms per stem.
21 Jul, 2017
Yes, that's most likely the reason. Dump it and use brand new compost/soil. Also, the seed used should be new as well, not left over from last year. Older seeds just don't do as well - not like new seeds.
20 Jul, 2017