We describe bases for the morphism spaces of the Frobenius Heisenberg categories associated to a symmetric graded Frobenius algebra, proving several open conjectures. Our proof uses a categorical comultiplication and generalized cyclotomic quotients of the category. We use our basis theorem to prove that the Grothendieck ring of the Karoubi envelope of the Frobenius Heisenberg category recovers the lattice Heisenberg algebra associated to the Frobenius algebra.Heis −1 (k) [Kho14], and then also to give a basis theorem for Heis k (k) [MS18] for all k 0. Unfortunately, the above method for proving linear independence fails for general A. The natural action of Heis k (A) is on modules for the cyclotomic wreath product algebras studied in [Sav20] (see also [KM19]). However, one can show by degree considerations that certain morphisms, expected to be nonzero in Heis k (A), must act as zero in any such module category; see [RS17, Rem. 8.11]. Therefore, until now, basis theorems in this general setting have remained conjectural, even in the important case where A is a zigzag algebra as in Example 9.1, when the Frobenius Heisenberg category is related to the geometry of Hilbert schemes [CL12] and categorical vertex operators [CL11].