"One of the diseases that can cause specific spots on the stems is pretty much only found in CA and it's called Alternaria Stem Canker."
 "Alternaria stem canker is primarily a problem of coastal-grown tomatoes in California although the disease occurs occasionally in other areas of the state in fields planted with infested transplants. The fungus survives on infected tomato debris. Infection occurs when airborne spores land on tomato plants or when plants come in contact with infested soil. Free water is necessary for spore germination and infection. Disease spread is favored by rains, dew, and overhead irrigation. Symptoms develop 7 to 10 days after inoculation and develop most rapidly at temperatures of around 77°F (25°C)."
- Tomato Diseases - Alternaria cankers
- Semena.org - Alternaria stem canker
- TomatoDirt - Fusarium wilt
- TomatoDirt - Verticillium wilt
- Tomato Diseases - Fusarium wilt
- Royal Horticultural Society - Tomato stem problems
- Missouri Botanical Garden - Tomato foliage problems
"Planting tomatoes in cold soil may cause the leaves to turn purple from a lack of potassium because tomatoes cannot absorb potassium if the soil is too cold"
Fertilizer numbers: N-P-K (nitrogen-phosphorus-potassium)
"Studies have found that the ideal ratio of those nutrients for flowering plants is 3-1-2. (That’s 3% Nitrogen, 1% phosphorus & 2% potassium.) So look for that ratio on the label of packaged fertilizers; anything close to a 3-1-2, a 6-2-4 or a 9-3-6 should be ideal."
- Growing Home Garden Tomatoes
- Espoma 18lbs Tomato And Vegetable Food - 3-4-6
- Jobe's Organic Vegetable & Tomato Granular Fertilizer, 2-7-4, 4-Pound Bag
- Miracle-Gro All Purpose Plant Food - 24-8-6 - 5 Pound
- Miracle Gro 100044 Tomato Plant Food, 3-Pound - 18-18-21
Preventing Herbs from Bolting
'Bolting' is when a vegetable flowers and goes to seed. In most cases, this is a negative thing and associated with a drastic decrease in the plant's productivity.
Articles on preventing bolting:
- Gardening Know How - Why Does Cilantro Bolt And How To Stop It
- the Herb Gardener - How to Keep Herbs from Bolting
- SF Gate - How to Prevent Bolting with Cilantro
- Bonnie Plants - Growing Cilantro
- The Brooklyn Gardener - What Do You Do When Your Cilantro Bolts? Get Coriander!
- GardenWeb - Stop going to seed!