The overall ratings of five chemicals stocks are down on Portfolio Grader this week. Each of these rates a "D" ("sell") or "F" overall ("strong sell"). This week, The Mosaic Company ( MOS ) falls to a D ("sell"), worse than last week's grade of C ("hold"). Mosaic produces and distributes crop nutrients to the agricultural communities located in North America and other countries. MOS also rates an F in Portfolio Grader's specific subcategory of Sales Growth. For more information, get Portfolio Grader's complete analysis of MOS stock. Intrepid Potash, Inc.'s ( IPI ) rating falls this week to an F ("strong sell"), down from last week's D ("sell"). Intrepid Potash mines and markets potash for use as a fertilizer. The stock gets F's in Earnings Revisions and Cash Flow. The stock price has fallen 9.5% over the past month, worse than the 1.7% decrease the S&P 500 has seen over the same period of time. As of Dec. 20, 2013, 15.9% of outstanding Intrepid Potash, Inc. shares were held short.