Possible Clues:

• Nurseryman's guarded forecast about hawthorn?
• 1620 craft
• Ship won't necessarily flourish
• Might for the present be a blooming boat
• Historic vessel takes weeks to sink after outbreak of fire
• Old craft might flourish
• For the present there might have been a lot of pilgrims on board blooming there (9)
• Could be in bloom across the Atlantic
• Hawthorn, say, is not certain to blossom
• 1 5's craft is quite likely to prosper