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Black bottoms on my tomatoes

Q: How do I prevent black bottoms on my tomatoes?

A: Tomatoes with black or brown leathery spots on the bottom side have succombed to blossom end rot.

It's caused by a calcium imbalance. The soil may have enough calcium (or not), but these conditions can prevent the plant from absorbing it:

  • inconsistent watering
  • root damage
  • cold temperatures/cold soil
  • excessive heat
  • too much nitrogen in soil (which lowers calcium uptake)
  • large amount of salts in the soil (which lowers the availability of calcium)
  • markedly acidic or alkaline soil (pH imbalance prevents calcium absorption)

There are several ways to prevent blossom end rot in tomatoes!

When planning your tomato crop
Carefully harden off young seedlings gradually to protect them from extreme temperatures and conditions. Select a planting area with good drainage, and avoid setting out plants too early in the season, which can expose them to cold temperatures and cold soil. Allow soil to warm before planting.

When planting tomatoes
Help good drainage by working in plenty of compost and organic matter into the soil before planting. This allows the plant’s root system a better chance to grow strong and deep. Add quick-release lime when planting tomatoes so that there’s plenty of calcium in the soil and it’s absorbed quickly. Tomatoes grow best when the soil pH is about 6.5.

When watering tomatoes
Keep your tomatoes’ water supply even throughout the season so that calcium uptake is regular. Tomatoes need 1-3 inches of water a week. They perform best when watered deeply a couple of times a week rather than superficially every day. Mulch plants once established to maintain moisture levels.

When growing tomatoes
Once blossoms emerge, apply tomato fertilizer that is high in phosphorus (the second number in a fertilizer’s three-number series), like 4-12-4 or 5-20-5. Too much nitrogen (the first number) or large amounts of fresh manure can prevent calcium uptake. Cultivate carefully around tomato plants to avoid damaging root systems. Try not to dig more than an inch or two deep around plants.

You can use these natural products specifically developed to treat, prevent, and slow blossom end rot in tomatoes: Enz-Rot Blossom End Rot (a concentrate that can make up to 8 gallons) and Tomato Rot-Stopicon (in a ready-to-use spray bottle.) Follow package directions for application.

Learn more about blossom end rot here.

Good luck and happy gardening!
Your friends at Tomato Dirt

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Aug 30, 2015
by: dssa

Add quick-release lime when planting tomatoes so that there’s plenty of calcium in the soil and it’s absorbed quickly. Tomatoes grow best when the soil pH is about 6.5.

May 07, 2015
by: Andy

The black bottoms on the tomato can be caused due to pest infestation. I think spraying copper sulphate solution can help you prevent this type of infection. Thank you for asking. This website is doing a great job by helping the tomato planters

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