How much calcium should I have in my soil to grow good tomatoes and peppers? - Ask Extension
I've had a backyard garden for a long time, but recently have been noticing a fair amount of blossom end rot and also curling leaves in my tomatoes (e...
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How much calcium should I have in my soil to grow good tomatoes and peppers? #854205
Asked October 27, 2023, 3:34 PM EDT
I've had a backyard garden for a long time, but recently have been noticing a fair amount of blossom end rot and also curling leaves in my tomatoes (especially), but also in my peppers. I was fairly convinced I had a calcium deficiency in my soil, so this fall I had a soil test done (two plots) at the Soil Test Lab -- for NPK and also for calcium and magnesium levels.
My calcium level in each plot seemed quite high -- 2462 ppm in one plot, and 2173 ppm in the other. I looked briefly online and found information saying I'd want calcium levels to be in the 450-540 ppm range. So now I am quite confused.
My question -- how much calcium should I have in my soil? Am I reading the soil test result correctly? It says my level in 5x what it should be. What can you tell me?
I'm also interested in what the magnesium levels should be -- the two plots in my garden currently show levels of 313 ppm and 406 ppm.
Hennepin County Minnesota
Expert Response
The symptoms you mentioned —blossom end rot and curling leaves on tomato plants is more a result of inconsistent watering than lack of calcium. Your soil has plenty of calcium but lack of water makes it unavailable to the plants. Overfertilizing can also contribute to this problem.
See:
https://hort.extension.wisc.edu/articles/blossom-end-rot/
Also see:
https://www.canr.msu.edu/resources/blossom_end_rot_tip_sheet
I would be very interested in your soil pH. Vegetables like these are best grown with a soil pH between 6.5 and 7.5. Also of interest is your fertilizing practices. Using an high NPK fertilizer can contribute to high levels such as yours. Tomatoes are heavy feeders but a low NPK such as 10-10-10 more frequently is best. And finally watering practices are key to preventing blossom end rot. You can have the right amounts of everything in your soil; but if water is insufficient to deliver it to the tomatoes, calcium will sit in the ground and leaves.
The good news is that correcting watering after seeing blossom end rot means that future tomatoes on that plant will be ok. The websites give more details.
See:
https://hort.extension.wisc.edu/articles/blossom-end-rot/
Also see:
https://www.canr.msu.edu/resources/blossom_end_rot_tip_sheet
I would be very interested in your soil pH. Vegetables like these are best grown with a soil pH between 6.5 and 7.5. Also of interest is your fertilizing practices. Using an high NPK fertilizer can contribute to high levels such as yours. Tomatoes are heavy feeders but a low NPK such as 10-10-10 more frequently is best. And finally watering practices are key to preventing blossom end rot. You can have the right amounts of everything in your soil; but if water is insufficient to deliver it to the tomatoes, calcium will sit in the ground and leaves.
The good news is that correcting watering after seeing blossom end rot means that future tomatoes on that plant will be ok. The websites give more details.
Hi Mary,
Thank you for getting back to me. I'd like to describe my practices, in case that sheds any further light.
- Our garden is approximately 17x16, with three paths within that perimeter (so less actual garden area).
- I sent two samples from two different plots in my garden to the U of M for soil testing. They showed a pH of 7.2 and 7.4, so it seems we are OK there.
- We compost our food scraps and some yard waste. I add our finished compost (not a lot, but some) to the garden each spring. I usually also buy a bag of finished compost at a garden store to spread on the garden.
- I also buy a bag or two of finished manure from a garden store. This year I spread a bag and a half. Some of that went into other small plots around the yard, but mostly in the main garden.
- I use Sustane most years -- just a small amount of their 4-6-4 fertilizer in the hole I dig for my peppers and tomatoes, nowhere else.
- Watering: Well, I read (somewhere) that I should put a good inch of water on the garden once a week, assuming no appreciable rain. I think I have been pretty good about doing that -- certainly I give it a good watering once a week, a little more frequently (like 5 day intervals) if it is very hot and windy. I try to "eyeball" the amount -- watching how long puddled water takes to be absorbed. Maybe I'm not giving enough water, but I would have thought I was. Is there a better way to deal with the kind of heat we've been having?
The other thing I'll mention is that this year we moved the tomatoes because we were having such problems with blossom end rot where they were. But we had the same problems this year. In fact, I decided to rip out a Brandywine tomato (my favorite!) because its leaves were so curled (still green, but dry-ish and curling) fairly early in the season. I think that would have been just before we got flowers, or just after -- but I believe it was before any fruit had set. The other tomato plants did better, but their leaves started curling later in the season, and we had quite a bit of blossom end rot, probably less that we had in the other location, but we still lost quite a few tomatoes. If only the squirrels would eat those!
Finally, curling leaves afflicted some of my pepper plants, and we also had a good number of Carmen peppers and poblanos that developed a soft blotch at the lower portion of the pepper, though not at the very end (I am not sure what that is from). And I had the lowest production from my jalapenos ever. and I noticed the leaves on several of those plants were a lighter green through a good part of the summer and into the fall. Meanwhile, our eggplants did very well -- no blossom end rot or other disease, no curling leaves, lots of eggplants.
Any further insight or advice you can provide would be greatly appreciated.
Mark Schultz
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Sent: Thursday, November 2, 2023 8:35 AM
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Subject: Re: How much calcium should I have in my soil to grow good tomatoes and peppers? (#0124130)
Sent: Thursday, November 2, 2023 8:35 AM
To: Mark Schultz <<personal data hidden>>
Subject: Re: How much calcium should I have in my soil to grow good tomatoes and peppers? (#0124130)
The lower production of the peppers is consistent with too much fertilizer. You need to cut back on the manure/compost. That along with the fertilizer explains why you get lots of green growth and less produce.
The high heat and drought has really required more than usual watering. One inch a week is not enough for the high heat and lack of rain. When I got blossom end rot early in the season I started watering 2-3 times a week. Much of that water evaporated from the leaves and the ground because I have an overhead system. It also matters HOW you water. A inch from a slow drip system is very different from an overhead sprinkler system. Think about adding fertilizer after the plants are established. You should not need fertilizer in the planting hole.
It was a challenge gardening this summer in the heat and drought!. Great that the eggplants came through.
The high heat and drought has really required more than usual watering. One inch a week is not enough for the high heat and lack of rain. When I got blossom end rot early in the season I started watering 2-3 times a week. Much of that water evaporated from the leaves and the ground because I have an overhead system. It also matters HOW you water. A inch from a slow drip system is very different from an overhead sprinkler system. Think about adding fertilizer after the plants are established. You should not need fertilizer in the planting hole.
It was a challenge gardening this summer in the heat and drought!. Great that the eggplants came through.
