Gilbert planted 3 + 1 + 2 = <<3+1+2=6>>6 herb plants.
He gained a basil plant when one of the basil plants seeded a new plant, so he had 6 + 1 = <<6+1=7>>7 plants.
The rabbit ate both mint plants, so Gilbert had 7 - 2 = <<7-2=5>>5 herb plants when spring ended.
#### 5