Question
bottom of tomatos turn dark brown why

Answer
Harold, your tomatoes are suffering from a condition called blossom-end rot. Blossom-end rot is caused by two things; uneven watering and a lack of magnesium and calcium in the soil. The condition is especially prevalent in dry conditions, which most of us have experienced much of the summer.

To prevent blossom-end rot, work in as much organic matter into your soil as possible. This would include compost, aged manure, dried grass clippings, shredded leaves, and peat moss. I also add 3 tbs. of epsom salts into my planting holes before transplanting. Scratch it in thoroughly to prevent the roots from burning. Epsom Salts are high in magnesium and help the roots draw in more nutrients, including calcium. I also supplement my fertilizing by spraying a solution of 1 tbs. epsom salts per gallon of water once per month. This really works.

Finally, water twice per week very deeply. Shallow watering causes the roots to reach to the top of the soil, resulting in weak plants and poor production. You can water more often during dry hot periods, but 1.5" per week should be your goal. Mulch generously with straw to hold in moisture and keep down weeds.

I hope this answered your question. Please write again if I can ever be of assistance.

Regards,

Mike