I planted my cabbage in late Feb. My cabbage leaves look very nice, very big, and very green(healthy), however they head is slow forming - The over all growth rate has been very slow. Any tips. These things need to hurray and produce. I want to plant other items in the space they are occupying. Please give any advice you think might help in speeding up growth. I am in a elevated garden with cow manure, compost, and very nice organic soil. I have also added some fertilizer as well.