The single biggest issue with tomatoes in the Willamette Valley is a lack of calcium. Virtually all soil in the valley is calcium deficient which causes our tomatoes to rot (blossom end rot) just before ripening. Another big culprit is cheap fertilizer. Cheap fertilizers (many national brands sadly fall under this label) use unstable forms of nitrogen in their mixes, especially water soluble fertilizers. Not only does the nitrogen become a plant-poisoning nitrite after a few days in the soil, it also restricts the plants ability to utilize calcium, compounding the blossom end rot issue. Good fertilizers use extra calcium, use stable forms of nitrogen as a significant portion of the mix, and contain the full spectrum of trace minerals needed for healthy plant growth. We would recommend Master Nursery Tomato Vegetable Food, or Dr Earth #5 for those who wish to stay Organic.
The next most important thing to remember when growing tomatoes is temperature. Tomato plants like it warm. Soil temperatures should be above 60 degrees, and night time temperatures should stay above 45 degrees. Anything less will significantly reduce the plants productivity, even when it does warm later in the season. Wall-O-Water will extend the season by about two weeks or about 3-5 degrees and is even more effective if it is put in place a few days before planting out.
Some other tips for growing the perfect tomato are: Set the plants deeper into the soil than you would other plants, covering the darkened section of the stem with soil, usually about 2 inches deeper than they are growing in the pot. Mixing a 1/4 cup of bone meal or lime in the planting hole will greatly reduce blossom end rot troubles - even with good quality fertilizers this is a big help for tomato, pepper, squash, pumpkin, cucumber and eggplant. Plant tall growing plants at a 45 degree angle to the soil. They will straighten after a few days and will develop stronger stems to support the big crop of tomatoes you are expecting later. Use red plastic mulch to increase your tomato crop - yeah, I thought it was silly at first too. But buckets of tomatoes later, I'm a believer! If you have a tomato that is to be wasted by blossom rot, cracking, slug damage, etc... use it as a quick wash-up before returning to the house. Crush the tomato in your hands and use it like soap on hands and forearms, it really cuts the dirt and green stains that come from working in the garden - the more over-ripe the better!