Historical clue formulations

• Plant ___ — 2018-08-24
• Plant ___ (suggest something) — 2014-10-05
• Plant ___ of doubt — 2010-10-03
• Plant ___ (give an idea) — 2009-11-19
• Plant ___ — 2009-02-28
• Thoreau work "Faith in ___" — 2004-08-22