Bottom rot on my tomatoes...

I'm in Southern Ontario Zone 5b (Niagara escarpment)
I have tomatoes in pots, two plants per pot, staked. Pots are 12" x 12" x 12" deep. A bit of a gravel bed on the bottom, maybe 3/4" thick. They face south and get 7 hours of sun a day. Soil is triple mix topsoil with 1/3 peat moss, and drainage holes at bottom of pots. These plants were planted by children in a school then we inherited the plants when school was out for summer. They flowered nice.
The bottoms of some of the tomatoes have gone black. A quick Google search suggests this is prolly due to lack of calcium but we have 25 hardness hard water. Our garden water is not run thru the water softener.
How can I determine if it's calcium defiency or not? What other possibilities can this be? The leaves never wilt and growth and foliage seem healthy. No bugs are eating the leaves. I've never grown tomotes before. Our herb gardens and flower beds are fantastic and are watered at the same intervals as our tomatoes.
If somebody wants pictures I can through up on the net if so.
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http://ipm.illinois.edu/diseases/series900/rpd906/index.html
Predisposing Factors Conditions favoring blossom-end rot also favor noninfectious leaf roll. Blossom-end rot is most common when there are: 1) prolonged dry periods; 2) frequent or heavy rains followed by an extended period of dry weather; 3) soil conditions unfavorable for uptake of calcium; 4) excessive soil salinity; and, 4) root damage from infectious diseases. Other factors favoring blossom-end rot include early planting in cold soils, poor fruit setting, and high temperatures. Any condition that reduces the ability of the roots to absorb water and, hence, soluble calcium salts predisposes the plant to blossom-end rot. Some factors that could affect the roots are root-rotting fungi, nematodes, underwatering, overfertilizing, root pruning due to cultivation or insect feeding, and lack of aeration due to soil compaction or overwatering. Losses from blossom-end rot increase when the soil contains an excess of total soluble salts in relation to soluble calcium salts. An excess of soluble ammonium, potassium, magnesium, or sodium salts reduces calcium uptake by the plant. Blossom end rot is rarely a problem in soils where calcium is available in proper balance with other available nutrients. Sometimes rapid luxuriant plant growth accentuates development of the disorder, because the new growth draws heavily on the available supply of calcium in the soil. Calcium is not translocated within the plant from older to younger tissues. Therefore, injury may appear on the blossom end of the young fruit, which is especially sensitive to a lack of calcium.
Some tomato varieties are much more susceptible to blossom-end rot than others (see Table 1).
--> **Generally, elongated pear and plum tomatoes used for processing and canning are prone to this disorder.**<--
Table 1: Incidence of some tomato varieties to blossom-end rot grown at the Dixon Springs Agricultural Center under irrigation.
Low Incidence High Incidence Losses less than 10% in severe years Losses of 15 to 30% or more in severe years Celebrity Big Boy Fresh Pak Castle King Jet Star Fantastic Manapal Independence Mountain Pride Supersonic Pik Red Surprise Sunny Whopper Winter Wonder Boy
As you can see, "blossom end rot" isn't that uncommon. Often gardeners will have trouble with it at the beginning of ripe fruit production, but then it usually goes away on its own.
--
- Billy
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The Henchman wrote:

Blossom end rot is a complex problem. Some highly qualified authorities are not sure exactly how it happens although they seem to agree it is related to calcium nutrition. There was a long thread on this at rec.gardens a week or two ago. To summarise:
- BER is an issue with calcium mobility which occurs most often when the plants are young and growing quickly. It often goes away without intervention as the plants mature. - It can be caused by lack of calcium in the soil or uneven watering which can interfere with nutrient mobility. - Some cultivars are more susceptible to it than others. - If adding lime to supply calcium do not overdose as this may raise the pH too far which will cause other nutrition problems.
David
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Please allow me to obscure this explanation.
<http://aob.oxfordjournals.org/cgi/content/full/95/4/571 "The symptoms, occurrence and search for the cause of blossom-end rot (BER) in tomato (Lycopersicon esculentum) have been described frequently in the scientific literature of the last century (see Brooks, 1914; Spurr, 1959; Saure, 2001). The majority of studies have identified a local Ca deficiency in the distal fruit tissue as the primary cause of BER (Lyon et al., 1942; Ward, 1973; Bradfield and Guttridge, 1984; Adams and Ho, 1992). For this reason, BER was considered to be a symptom of a Ca-related physiological disorder (see Shear, 1975; Bangerth, 1979; Kinet and Peet, 1997). However, the induction of BER in modern glasshouse tomato production is rarely caused by insufficient Ca in the feed. More often, BER occurs in plants with an adequate Ca supply when grown under conditions that either (a) reduce the transport of Ca to rapidly growing distal fruit tissue or (b) increase the demand of the distal fruit tissue for Ca by accelerating fruit expansion (Ho, 1998b). In practice, BER can be prevented by increasing Ca transport toward the fruit by reducing canopy transpiration (Li et al., 2001) or by canopy Ca sprays (Geraldson, 1957; Wilcox et al., 1973; Wada et al., 1996; Ho, 1998a; Schmitz-Eiberger et al., 2002). Nevertheless, since BER may occur in plants and fruits with apparently adequate tissue Ca concentrations, predicting and preventing the occurrence of BER in glasshouse tomatoes from measurements of their Ca status has not always been effective.
---> This has led to a recent opinion that Ca nutrition is neither a primary, nor an independent factor in the development of BER (Saure, 2001)."<--- (arrows added for emphasis)
Other than that, David has given you the working theory of BER. Paste (plum) tomatoes seem to be the most susceptible, and most BER will diminish in severity, or go away altogether with a little time.
--
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When you say go away, do you mean leave well enuf alone and it'll grow out of this phase?
Is there a difference between municipal groundwater ( hard water from limestone sources) and rainwater used for watering fruits and vegetable plants?
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BER will often correct itself.
Were I live, just about all our water, agricultural and drinking water comes out of our river.
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The Henchman wrote:

Often it will.

Yes there is a difference in content of the water but whether the consequences of using one or the other are significant depends on the stituation.
The result of using hard water is most often seen in pot plants where much of the water added evaporates leaving salts behind and where there is little or no leaching to flush it out. In some cases this will be seen as a white crust in the pot or round drain holes. How much this affects the plant depends on what the salts are and the sensitivity of the plant.
David
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