Tomato Canning Tips from Irma Harding. Select only firm, disease-free, preferably vine-ripened tomatoes. Do not can tomatoes from dead or frost-killed vines. Green tomatoes are more acidic than ripened fruit and can be canned safely with any of the following recommendations: Add 2 tablespoons of bottled lemon juice per quart of tomatoes. For pints, use 1 tablespoon of bottled lemon juice.. http://www.farmersmarketonline.com/bk/CanningPicklingandFreezingwithIrmaHarding.htm.