Possible Clues:

• Marsh plant providing a variety of materials
• Materials processed in plant
• A wisp of trailing cirrus cloud, often indicating high winds in the upper troposphere
• Plant needs a support, external post
• Front in Med is to weaken, admitting a break in the cloud
• A break in correspondence that's rooted in Slough, say?
• Wedged into post, a support for plant
• Long, narrow cloud
• Cloud of materials blowing about
• Tall marsh plant