。
She has plenty of seeds ready to plant in the spring.
Literal
She [topic-は] spring [in-に] plant many [of-の] seeds [object-を] is-prepared.
春に植える is a relative clause modifying たくさんの種 — 'seeds (that she will) plant in spring.' Japanese relative clauses precede the noun they modify, with no relative pronoun needed. 備えている means to be prepared or to have something in stock, using ~ている for the resulting state of having prepared. The sentence captures a moment of quiet domestic readiness.