In Northern Europe , the northern states of the U.S. , and the South Island of New Zealand it will grow best if sown under glass in a peat pot . It can be planted out in late spring\/early summer , when there is little risk of frost . In Northern Europe , Canada , the northern states of the U.S. , and the South Island of New Zealand it will grow best if sown under glass in a peat pot , then planted out in late spring\/early summer ( when there is little chance of a frost ) .