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Fri Oct 2, 2015, 01:57 PM

Lowering pH and adding Ca

We set up a container garden to try and grow tomatoes as a first-time "let's see if we can grow anything" exercise.

The plant exploded, the greenery was doing very well, we actually destroyed two tomato cages because the plant got too heavy for them.

...And we ended up losing all the fruit to blossom-end rot. Actually testing the soil (what a novel idea!) showed that the pH is high for tomatoes (7.4).

Do you guys have recommendations for lowering the pH and adding calcium to the soil? And how do I figure out how much to put into the container?

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Reply Lowering pH and adding Ca (Original post)
jeff47 Oct 2015 OP
Elad Oct 2015 #1
Curmudgeoness Oct 2015 #2
Major Nikon Oct 2015 #3

Response to jeff47 (Original post)

Fri Oct 2, 2015, 03:25 PM

1. If you want to try and save your harvest

you'll need a foliar spray supplement for blossom-end rot. If you're trying to do it better next time, you'll want to use a combination of gypsum and lime.

pH and calcium is a complicated and much misunderstood topic. The simple answer is that lime raises pH, and gypsum will work to lower it. Kind of. Both add calcium, technically, but your soil might not hold the calcium. pH is a measure of cations (calcium being the main one) in the soil, and the sulfur in gypsum essentially allows those cations to be stripped away, lowering the pH because the calcium is being washed away when the soil is watered. But your pH is high, suggesting your soil would have trouble binding the calcium anyway.

What I'd suggest instead is to forget about your pH next time and use a good, high-organic-matter potting soil, with a complete organic fertilizer that has the proper amounts of calcium and magnesium naturally. Further reading here:
http://www.growgreatvegetables.com/fertilizers/a-great-organic-fertilizer-mix/

Edited to add that growing tomatoes in containers often does lead to blossom-end rot due to the smaller amount of soil. A root bound plant won't be getting the nutrients it needs. It can be done, but it's more difficult.

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Response to jeff47 (Original post)

Fri Oct 2, 2015, 06:26 PM

2. What kind of soil did you use?

I have done container tomatoes for several years, and I have good luck. I do use a potting soil, and mix in my own compost and mulched leaves from the spring cleaning. I have oak leaves, which are acidic and tomatoes seem to be happy.

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Response to jeff47 (Original post)

Sat Oct 3, 2015, 02:42 PM

3. Here's something to consider

Even if you get your soil pH corrected, your water supply may be quite high in pH, so the actual problem may be the water you are giving the plants. You can check your local municipality's water quality report to get an idea of what the pH is. You should be able to find it online.

Assuming you are hand watering your plants daily, you can start using a liquid fertilizer intended to be added to daily waterings. There are a number of them out there and you can find them either online, your local hydroponics store, or sometimes at garden outlets. Wherever you find such fertilizer, you can also find liquid CaMg. This will raise both the calcium and the magnesium of the source water, and the directions are right on the bottle as far as how much to use.

Once you have your watering batch mixed, you can lower its pH with a few different methods. One of the cheapest is hydrochloric acid sold in pool supply stores as muriatic acid. One gallon of this stuff goes a long ways. Roughly 1/4 cup of this stuff will lower the pH of a 55 gallon drum of water by 1 or 2 points. So you'll need a method to measure pH of your water. You can get a pH testing kit at pet supply stores. I have a digital pH meter which wasn't all that expensive and makes life a lot easier if you are using it often. You have to calibrate the digital meters often, like once per week, so you'll also need a bottle of calibration buffer if you get one.

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