Tomato Blossom End Rot
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A water soaked spot at the blossom end of tomato fruits is the classic symptom of blossom end rot. This relatively common garden problem is not a disease, but rather a physiological disorder caused by a calcium imbalance within the plant.
In this feature, garden authority Gayla Trail, the creator of YouGrowGirl.com, answers frequently-asked questions and offers gardening advice.
My heirloom tomatoes are starting to ripen but they have ugly black spots on the bottom. What is going on? Can I still eat the good parts and just cut off the spot?
Sounds like your tomatoes have got a case of blossom end rot, a very common condition that is caused by a calcium deficiency that leads to disfiguration of developing fruit. In general, the condition is not caused by a lack of calcium in the soil, but because the plant is unable to take up the calcium that is already there due to drought or an erratic watering schedule.
Do not despair. A lot of gardeners (myself included) have found themselves in your position this summer. Large parts of North America have been experiencing record highs, prolonged heat waves and a disturbing lack of rainfall. Keeping plants happy through these extremes has been a struggle, one that is made worse if you are growing in pots. To answer your question, yes you can cut off the rot and eat what’s left of the fruit – it won’t kill you or make you sick. However, I find that the remaining fruit tends to be mealy and poor quality. If you do eat it, do so right away; do not try to can or preserve it.
Fortunately, blossom end rot is not a viral, bacterial or fungal issue – you still have plenty of time to turn things around and produce primo tomatoes with a bit of due diligence.
How to Water Tomatoes
Tomato plants are thirsty creatures and their thirst only increases as they begin to set fruit. The trick to keeping them happy is to water deeply, but infrequently. This means that rather than sprinkling or pouring a little water on everyday, it is better if you give them a really good, long soak right at the soil line every few days, more or less, depending on growing conditions.
Potted plants generally need to be thoroughly drenched every single day, especially during a heat wave when the soil dries faster than the roots can soak it up. I give mature, potted tomatoes that are in the fruiting stage roughly four litres/one gallon of water during the hottest days of summer. Administer it slowly rather than all at once so that the soil has a chance to rehydrate.
Tips and Tricks
If you’re having a hard time keeping up with watering demands, I would suggest employing a few if not all of the DIY waterwise techniques I have outlined here. Over the long term, mulch will help to improve the soil content over time, which can lead to better water absorption and retention. In the short term it will prevent the sun from heating up the soil and drying it out quickly before you’ve had a chance to water.
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In the event of extreme heat, drip irrigation will help keep the soil from becoming completely bone dry. If you have to go away for a day or two, fill up bags with water and secure them closed. Poke tiny holes into the bottom of each bag with a pin and set them down onto the soil surface around the plant. Instant, and free drip irrigation!