Best way to add calcium to soil to prevent blossom end rot?

Tomato    SC

I have a tomato growing question. I have experienced problems with blossom end rot on past tomato crops and I would like to try growing some again this year. If it is caused by a calcium deficiency then what is the best way of supplementing the soil?

Posted by: Melanie Young (10 points) Melanie Young
Posted: April 1, 2013

Mohammad Kafafi commented,
The movement of Calcium from the soil to the plant is only up, like elevator going only up, so if it goes to the leaves then it will stay there and will not go to fruits..... for that is very important to apply Calcium by foliar application specially during fruit set phonological stage not only to solve the problem of blossom end rot, but also to increase the cell division inside the fruit at this stage.... And by foliar application is better Calcium chelated by carboxilic acid to increase the efficiency of Ca movement inside the plant.
over 7 years ago.


While blossom end rot is caused by a lack of calcium to the developing fruits, it doesn't mean there isn't enough calcium in the soil. It is most often related to an inconsistent amount of water in the soil or being taken up by the plant. Calcium is brought to the fruit in the water the plant takes up from the soil so allowing the soil to dry out too much between waterings can cause blossom end rot. Pot-grown tomatoes are especially susceptible.

Once fruits begin to form, water to supply 1-2" per week from rain and irrigation combined. Water deeply 1-2 times per week rather than frequent shallow waterings to promote good root growth. Water is drawn into the plant partly in relation to the amount of water lost from the leaves via transpiration. Transpiration slows down when there is high humidity, resulting in less water being needed from the soil. Less water from the soil = less calcium coming into the plant so extended periods of high humidity can also result in blossom end rot.

The best way to see if there is a pH problem or calcium deficiency in the soil is to get a soil test done. The best pH for tomato is 6.0-7.0 and if it's already there, you don't want to add lime which will raise the pH. A mulch can help the soil retain moisture. Other tips include not planting the tomatoes when the soil is too cool (affects early fruits), don't overfertilize with nitrogen, and be careful not to injure the roots if cultivation is needed near the plants. Some sources recommend calcium chloride sprays on the foliage but use caution with these. They can cause plant injury and some reliable sources say they don't really help.

Posted by: Joan Allen (6 points) Joan Allen
Posted: April 2, 2013

deactivated commented,
Joan, can you tell us more about the "reliable sources" mentioned at the end? Would be useful to see the resources.
almost 11 years ago.

Joan Allen commented,
http://www.caes.uga.edu/publications/... sorry for delay in responding to this...my 'reliable source' is at this link, a ways down in the article/fact sheet under diagnosis question #2.
almost 11 years ago.

Nicodemas Zabron commented,
I agree with you Joan, from my experience, spraying of calcium based foliar fertilizer alone has no significant effect on the tomato crop but when combined it with any fungicides the burning effect around the leaves margine is more likely to occurs
7 months ago.

Often a deficiency, or lack of availability of Magnesium results in decrease availability thereof, directly influencing the uptake (thus availability) of Calcium. Gypsum indeed functions well in that it results in the release of Magnesium from chelates (bound carbon) resulting in increased Mg/Ca exchangeability, and hence uptake in the plant.

Alternatively, a foliar Calcium application during or just after flowering may suffice. Calcium Metalosate works well.

If you suspect (after soil testing) that the Magnesium levels are low in the soil, add a handful uf Epsom salts to the base surrounding the stem and wash in with water. This will "loosen up" existing Ca in the soil allowing for more effective uptake in the plant.

Ensure that this is done early in the growing period so you can gauge progress.

Posted by: Cornelis (2 points) Cornelis
Posted: April 4, 2013

Joel D Morris commented,
I always put about a handful of Epsom Salts around my tomato plants and never have a problem with blossom end rot. Simple & effective & cheap.
almost 9 years ago.

I use washed crushed eggshells in water around the tomatoes. Also barn lime placed around the plant when it is about to flower will help sometimes.

Posted by: chris hedding (1 point) chris hedding
Posted: April 1, 2013

Jim Burke commented,
How do I deal with bacterial spot
over 1 year ago.

Lime and gypsum work well- I use the pelletized stuff because it's easier to use and not a dusty, plus it is coated in molasses, which is another good source of calcium. When you feed your plants, you can add plain yogurt at 2 oz per gallon of water, and molasses as well, for more calcium plus some carbohydrates, at a rate of 2 oz per gallon of water. Eggshells work well, but take a while to break down, so the calcium is not available to the plant right away.

Posted by: Bradley Cahill (1 point) Bradley Cahill
Posted: April 1, 2013

Wurgulf commented,
Gypsum is my go to. I used to think it was silly to mix some in the planting holes at transplanting but I do now. And I like the results. This year I'm looking to do some dairy based spraying on my own plants and soil.
about 11 years ago.

Are there any good spays you can put on the plants to help. I think I have seen a few but never used any of them.

Posted by: Jack Campbell (1 point) Jack Campbell
Posted: January 10, 2017

David Hughes commented,
you might wish to ask a separate question about this if you are looking for dealing with your own plants
about 7 years ago.

Apply calcium base fertilizer and regular watering of tomato

Posted: October 4, 2023

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