Before growth boosters, the most important thing for essence berry bushes (and any of the oreberry bushes for that matter) is to grow them in pitch darkness. Encase them in blocks or use blackout curtains and that'll do more than anything else, other than the old OP automated watering can in older versions. For up-to-date Monster (i.e. no Ars Magica), your best option might be Thaumcraft Lamp of Growth screened by blackout curtains, since the light it produces hinders the growth of the bushes.
They dont NEED darkness, but definitely grow quicker.Essence bushes don't requite pitch darkness? Atleast mine grow out in the open. I think it's the ore berry bushes are the ones that need pitch darkness.