Blossom End Rot and What To Do

When the fruit first begins to form in your vegetable garden you may notice a condition where the blossom ends of the fruit turns brown to black then begins to rot away. This can happen to a number of different vegetable garden producers like tomatoes, squash, peppers, and more. Aptly named “Blossom End Rot”, this condition is nothing to be overly concerned about. It’s disappointing to see something you’ve been eagerly awaiting for weeks get seemingly ruined – but it is only temporary!

Blossom End Rot on Summer Squash

What Causes Blossom End Rot?

Blossom end rot is a calcium deficiency that prevents the proper formation of cells in the fruit. Just like people, plants need nutrients like calcium for proper growth. The calcium deficiency can be cause by a couple things but is usually an issue with too much water not allowing the plant to bring in calcium through its root system. You will see blossom end rot mostly at the beginning of the plant’s fruit production when the spring rains have been fairly frequent and soils tend to be saturated with water.

Plants Affected by Blossom End Rot

Some common plants affected by blossom end rot are tomatoes, peppers, squash, and zucchini.

Common Causes of Blossom End Rot

Anything that prevents the proper absorption of calcium from the soil can cause blossom end rot. That includes irregular much water, pH issues, too much nitrogen, the soil is too cold, or even damaged roots.

How Should You Treat Blossom End Rot?

The first instinct anyone has with any problem is to DO SOMETHING but that may not even be necessary. Blossom end rot does not always require treatment. There are some possible causes that may require a little troubleshooting and the treatment for blossom end rot depends on the cause. Step one is to diagnose the cause!

Irregular Water

At the beginning of the season plants may not be able to bring in enough calcium due to frequent rains or over watering which creates an over saturated soil situation which prevents the uptake of nutrients and causes the blossom end rot. Correcting the watering situation is usually all that needs done! Dispose of the fruit as soon as the rot begins to form so that the plant doesn’t waste time and energy on producing useless fruit.

When blossom end rot is caused by watering issues you don’t need to treat or amend the soil. As you adjust your watering schedule or the weather changes the conditions better and blossom end rot disappears. In most soils there is plenty of calcium for plants to use and no need to amend the soil to add calcium. Adding calcium to the soil probably won’t hurt anything but it most likely won’t help either.

pH Problems

If your soil does not have the optimal pH the roots will not absorb nutrients from the soil properly. Watch for discoloration of the leaves on the plant as an additional sign. Adding some lime may help adjust the pH to a more balanced acidity if the soil is too acidic. (Lime changes acidity by making soil more alkaline)

Nitrogen Issues

Nitrogen is used by plants for leaf growth. If you have amended with a high nitrogen fertilizer or compost with too much nitrogen the plants will work on making leaves and not on making fruit and causes blossom end rot. The fruit that forms may be deficient in the nutrients it needs. To fix this fertilize with an organic fertilizer that has low nitrogen, high potassium, and high phosphorus.

For an indicator of too much nitrogen look for the leaf growth. If there is a ton of leaf growth but only a few flowers this could be the cause.


The Soil is too Cold

Warm season plants like the soil temps to be above 50 degrees. If the soil temps are too cold it inhibits the uptake of nutrients. Typically the answer to this issue is to plant your summer vegetables at the right time. That’s usually about 2 weeks after the frost date and the sun has had time to warm the ground properly. You could also add a mulch to help keep the warmth in the bed.

Root Damage

If the roots were damaged through either cultivation or by animal pests it could be a cause of blossom end rot. Eliminate the pests and take better care during cultivation and the plants will eventually recover.

Does Amending the Soil Help Blossom End Rot?

Often you’ll see tips like adding bonemeal or lime to the soil. You might also have been recommended to fill a newly emptied milk jug with water and water the plants with the milk-water or even add tums. I’ve done these corrective measures too and the result is pretty much the same as when I’ve done nothing: the first set of fruit has blossom end rot but the second set is perfectly fine.

As I mentioned previously the MOST common cause of blossom end rot is the irregular watering. If the spring has been extremely wet it is likely the main cause of the issue.

Sometimes it is hard to do nothing and just wait on things to get better (being patient can be hard!) Think of it like a doctor prescribing antibiotics for a virus that will run its course in 3-5 days and the doctor tells you that you’ll be better in 3-5 days. It may make you feel better to do something but it really wasn’t going to help.

The truth is there is probably plenty of calcium in the soil already and the plant is just having trouble accessing it. Amending the soil may not help at all. If your soil has trouble with drainage and retains too much moisture you may want to add organic matter that improves the drainage issue.

In the case of a poor pH amending the soil with lime may help. You should consider testing the soil for the pH to see if this is the issue first before proceeding with adjusting the pH.

When to Amend the Soil

If blossom end rot persists throughout the season then you may need to add something to the soil but keep an eye out for signs of drought. Dry conditions prevent the roots from bringing in nutrients and can be a cause (irregular watering). If it hasn’t been dry or you have kept a good watering schedule then you may need to have your soil tested to see exactly how much and what kind of amendments the extension service in your area recommends.

Have you seen blossom end rot on your plants this year?

2 thoughts on “Blossom End Rot and What To Do”

  1. My squash hasn't a chance anyway in the desert heat in El Paso. Once June arrives the thin mountain air makes el sol a blowtorch on plants! But just wondering, too, if you could draw the same "blossom end rot" analogy on what's happened to my Star Jasmine and Honeysuckle vine blossoms? I've even built them some arbor shade. Bloomed prolifically during April and May, and then once that heat hit it looked like they went into an immediate retreat. Wilty, much of the vines turning brown, dead; and all those beautiful blooms shriveling to a blackened end. Could this be because I've watered too much during the spring? We sure don't get enough rain to amount to anything here! Thanks.

    1. Hi Dan,

      Interesting question but I think it may be more related to the plant just becoming too dry with the adverse weather conditions. I suspect the intense heat you describe contributes to a massive decline for your Jasmine and Honeysuckle rather than an issue involving too much watering in the spring.

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