Nutrient deficiencies can also cause tomato plant problems. Here are symptoms to look for and suggestions for treatment:
Symptoms: Yellowing between leaf veins with the older leaves affected first.
Treatment: Spray, drench or sprinkle magnesium sulfate around the base.
Symptoms: Blossom End Rot--a hard, dark flattened patch appears at the blossom-end of the fruit.
Cause: Can be due to inconsistent watering. Can also happen during a high-growth stage when more calcium goes directly to the new, growing tissues
Treatment: Sometimes this will solve itself, however make sure to Water consistently and apply a layer of mulch on the soil.
Symptoms: Stunted growth and older leaves turn yellow.
Treatment: Apply dried blood meal, well-composted manure or soybean meal.
Symptoms: Purple cast on leaves--seedlings often have this but outgrow it once they are transplanted their roots grow to reach this nutrient in the soil.
Treatment: Apply bonemeal
Symptoms: Older leaf margins turn yellow and brown. Dead parts become crunchy and may fall off.
Treatment: Apply Green sand, kelp meal or wood ashes--keep in mind that wood ashes will raise the pH of the soil.
8 Cagey Culprits. May/June 2003. Organic Gardening Magazine. Pages 29-30.
Common Problems Solved. April 2007. Organic Gardening Magazine. Page 65.
The complete Book of Vegetables Herbs and Fruit. The Definitive Sourcebook for Growing, Harvesting and Cooking. M. Biggs, J. McVicar, B. Flowerdew. 2004 Edition. Kyle Cathie Limited. Pages 125-130.