hey joe it could be one of the few following issues. first check your soil PH, 6.5 to 7.2 is best. You can treat with just a tad bit of Lime to your soil mix if your to high (no pun intended). Second check your potting soil mix you may be a bit low in one of the two following Manganese, or Iron. Third check your water source for any impurities and free radicals. Trouble shoot and get back with me to let me know how the Kids are doing.