Sounds like your having the same trouble I use to have with my spinach. Most varieties do not grow well in the summer and winter and must be grown spring and fall months in shade for best results. There are a few varieties that can be grown in the summer with the rest of garden which include my favorite the Olympia Hyrbid Spinach plant. I also noticed that it is hard to grow single plants by themself and is much easier if you grow several plants close together to offer shade for eachother. This will help produce the best results for you.