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More water for potted tomatoes

Published: Thu, August 9, 2018 @ 12:00 a.m.

Q. I planted a tomato in a big pot. The tomatoes get ripe, then the bottoms get calloused and hard. Is this a calcium deficiency? Over/under watering? How do I fix this?

Pat from Youngstown

A. This is the dreaded blossom-end rot. It is a common disorder, usually caused by under watering. The root cause is a calcium deficiency, but this deficiency is usually caused by under watering.

Watering is a big deal when it comes to tomatoes.

Since you are growing your tomatoes in a container, there can be some other issues affecting the plant’s growth. First, the container should be at least three gallons, even better if it is five gallons. This will ensure the plant has enough room for proper root growth, allowing it to take up enough water for fruit production. Next is the water itself. There is usually enough calcium in our municipal water supply to provide adequate nutrition for your tomato plants. Finally, yet another issue may be the use of potting mix. Some potting mixes may not provide enough calcium, but the water should be doing that job.

So, if you’ve taken care of all of these potential culprits – consistent watering should be your major focus during the growing season.

Consistent watering is providing a minimum of 1 inch per week, closer to 2 inches per week when fruit is on the tomato plant. But that recommendation is for gardeners growing their tomatoes in the ground. Since you are growing in containers, providing a consistent water supply is a completely different task. The sides of containers are constantly exposed to air and sunlight. These two factors dry out the soil within the container very quickly. Furthermore, the potting mixes most of us use in our containers do not have significant water holding capacity. Thus, watering may need to be done nearly every day to provide enough for a tomato plant.

You should use your finger every day to check the moisture level in the container. Just put your finger down into the soil. If it’s dry – give it more water. Many of us don’t expect containers to dry out that quickly, but a rapidly growing tomato plant and hot weather speed it up significantly.

Now, back to calcium. Yes, the lack of enough calcium to be taken up by the plant is what is causing the fruit to have black, leathery ends. But the major cause of the deficiency is not enough water going through the entire plant. Water transports the calcium to the fruit to form the cell walls for a delicious tomato. In times of water stress, water goes to the leaves first, not the fruit.

There is an excellent, detailed and yet simplified factsheet on this topic here: http://go.osu.edu/endrot.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office plant and pest clinic at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m., to noon Mondays and Thursdays.

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