After I diligently hand-weed -- pulling stolons, leaves, flowers and roots -- my garden, these weeds return within a few weeks and overtake my garden in a month or two.

Euphorbia peplus (Petty Spurge)
Senecio vulgaris (common groundsel)
Medicago lupulina |Black Medic)
Galium aparine (cleavers, velcro weed)

Beside weeding, is there a soil condition that would encourage these weeds?