When inserting the scion into the rootstock, align the cambium layers together.
Literal
Scion [object-を] rootstock [to-に] inserting time, cambium [object-を] overlapping [manner-ようにします].
Highly specialized horticultural vocabulary: 穂木 (ほぎ, 'scion' — the cutting to be grafted), 台木 (だいぎ, 'rootstock'), 形成層 (けいせいそう, 'cambium layer'). 重ね合わせるようにします ('do it in a way that overlaps them') is the instructional pattern. A technical sentence that most Japanese natives would struggle with unless they garden — a reminder that difficulty isn't just grammar.