The formation of hydrogels on surfaces is a frequently used strategy to render these surfaces biorepulsive. Hyperbranched polyglycerol layers are a promising alternative to the frequently used polyethyleneglycol layers. Here, we present a strategy to covalently graft polyglycerol layers onto surfaces by first depositing an aminopropylsiloxane layer, which then acts as initiator layer for the ring-opening polymerization of 2-(hydroxymethyl)oxirane (glycidol). For silicon surfaces, the resulting polyglycerol layers start being biorepulsive for E. coli at a thickness of 2 nm and reach their highest bacterial repulsion (98%) at thicknesses of 7 nm or larger. This deposition strategy promises general applicability because the formation of aminopropylsiloxane layers has already been described for many materials.