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We have blossom end rot problem which is apparently a calcium deficiency. We have some builder's lime which I am told is calcium hydroxide and would like to use that as the calcium source. We can't afford to buy anything else so we need to use that. We have a few questions: 1. do we have to do anything to the lime to make the calcium available, to 'unlock it' so to speak? 2. what amount do we need to apply to correct blossom end rot? 3. do we have to be concerned about PH change and if so how do we compensate for it?

The goal is to not have it change the ph and that the calcium would be available for the plants right away. Thanks.

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    I would suggest gypsum ( calcium sulfate ). It can be acidic but not a problem unless your soil is already more acid than about pH 6.5. – blacksmith37 Jul 3 '20 at 20:03
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    You definitely need to be concerned about pH. Water reacts with builder's lime to form a solution with a pH of between 12 and 13, which is alkaline enough to cause chemical burns if you get it on your skin, not to mention what it would do to a plant! – alephzero Jul 3 '20 at 20:36
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    Unlike builder's lime, agricultural lime is simply powdered limestone rock, and is perfectly safe to handle. – alephzero Jul 4 '20 at 2:06
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Your tomato plants may not need to have calcium applied to the soil they're growing in; an erratic or inadequate watering regime is most often the cause of blossom end rot, as well as some varieties of tomatoes being more susceptible to this problem. Without regular and sufficient supplies of water, the plant is unable to take up calcium from the soil and transport it to the fruits, and blossom end rot may occur, see here https://www.rhs.org.uk/advice/profile?pid=395

Hydrated lime is not an ideal source of calcium and is more often used to alter soil ph, usually in unplanted ground. The other use is to stop tomato wilt caused by fusarium disease, but care must be taken when using it see here https://homeguides.sfgate.com/can-hydrated-lime-cause-tomatoes-wilt-104796.html

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