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Blossom End Rot & Poor Pollination Solutions

July 24, 2015

In the height of the annual vegetable growing season, we see a lot of photo request pleas for what may be blossom end rot. Frustrated veggie gardeners who have worked diligently to get their tomatoes, squash and other edibles to produce flowers and fruits are suddenly dismayed to find these shriveled and blackening flower ends on their crops.

Two very common culprits result in the flower-end of your homegrown edibles turning brown and shriveling: blossom end rot and poor pollination. Each has a different cause. Understanding those causes is the key to remedying the issue before the season passes and your entire crop is lost. And, yes, there are ways to get past both problems during the growing season. And, there are ways to keep them from repeating in the future.

Let’s take a look at samples of both problems:

Example of poorly & well pollinated zucchini fruits

Here are two zucchini fruits. The tiny one is shriveling due to poor pollination, not blossom end rot. The large one was well pollinated, resulting in a rapidly growing squash fruit.

Tomatoes with Blossom End Rot

When fruits like these paste tomatoes are pollinated & maturing & then the bottoms begin to turn black, that’s blossom end rot. Not every end-rotten tomato in a cluster or on every plant will show this way. Sometimes you’ll cut into a ripe fruit only to discover the rot. Dang it!

Read on to see the progression of each issue and get our tips to fix both problems during the growing season and help deter it before it starts in years ahead.

Poorly pollinated fruits show their hand much more rapidly than fruits with blossom end rot.

Tonda panada squash ready for pollination

Squash & its relatives often suffer from poor pollination. Female squash blossoms like this Tonda Panada begin with a small, immature fruit at the base of the to-be-pollinated flower. After the flower is pollinated, this fruit will begin to expand quickly & the stem attaching it to the vine will become stronger to support the growing fruit.

Squash ripening on vine

Within a day of the flower opening & bees pollinating it, this Tonda Panada fruit has begun to expand & its supporting stem has begun to strengthen to support it on the vine as it ripens.

Poorly pollinated squash

If  squash isn’t well pollinated, a fruit will begin to yellow & shrivel quickly, sometimes turning brown or black at the flower end over time as shown in the zucchini photo above.

If this is happening to your squash, zucchini, melons or pumpkins, the problem isn’t blossom end rot. Instead, it’s time to do more about pollination!

  • Stop applying pollinator-detrimental ‘cides.
  • Add plants nearby that pollinators love such as borage. (Get our free Pollinator Favorite Things handout for more planting ideas.)
  • Stop overhead watering when female flowers are open. Squash tend to open flowers early in the day & close the flowers by early afternoon*. Most female squash flowers only open for one day. If you apply overhead water during this time, bees may choose to do their work where “rain” isn’t plopping on them, which means your flowers won’t be pollinated. Too, if the flowers fill with water, it can be more difficult for bees to do their job once watering is done.
  • Consider hand-pollinating. If your flowers open at a time when bees just aren’t around, you may want to take matters into your own hands. Grab a tiny paint brush or a makeup brush (that you use only for pollinating), swirl it through the pollen in a male squash flower and lightly dust it across the interior of a female squash flower.

Is your problem actually blossom end rot? Keep reading for a photo guide and tips to remedy this common food gardener’s woe.

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Blossom end rot is caused^ by plants being unable to access needed calcium. In some areas, like ours, soils are known to be deficient in calcium. In some situations, soil may have sufficient calcium, but other parts of the soil science are such that plants can’t access needed calcium. And, some varieties of tomatoes are more likely to develop end rot than others. So, what to do when your crop is forming fruit, and it’s too late to start all over for the season?

Ripening Blossom End Rot Tomato

Blossom end rot may show up while fruits are green, as they ripen or even once you cut into an otherwise perfect fruit. There are ways to avoid it or minimize it in your garden.

  • Apply calcium! There are products available that provide this plant nutrient and are sold for exactly this purpose. Or, simply try applying some lime — taking extra care if you choose a caustic hydrated lime or other types of lime that can burn you. Read the package to know what you’ve got and how to handle it properly! Mix about 3/4-1 cup of lime into a large watering can. Allow it to sit overnight. Then, pour it over your plants as a foliar feed and soil soak. Done once, new fruits should form without end rot.
  • Remove any tomatoes on the vine that are showing signs of end rot. If you don’t remove the rotten fruits, your plants will exert precious energy on these nasty bits instead of on less damaged ones. (The not-rotten parts of the fruits can be eaten, if you cut out & discard the nasty bits.)
  • Don’t fertilize unless you know your garden needs it. Over-fertilization can be wasteful and can create soil nutrient imbalances that further compound any problems, and unused fertilizer can create soil and water contamination problems.
  • Add egg shells to your soil. Adding egg shells, shellfish shells and bonemeals to your soil can help raise your calcium levels. Because it takes a while for these shells to breakdown and release calcium to the soil, adding them may not help things turnaround on a fruiting plant, but adding them consistently over time can help year after year as can liming your soil.
  • Get a soil test. Again, it may be too late for this season’s crop, but testing your soil is the best way to understand how and if your soil is out of balance in any way. Liming may help your existing crops, but it does more than just add calcium to your soil. Over time, it can also change your soil’s pH. And, even if you apply lime to adjust pH, it may not be quite enough to keep your tomatoes, peppers, eggplant and other nightshades from succumbing to blossom end rot.
  • Grow tomatoes that are less suceptible to end rot issues. We’ve found that paste tomatoes are the most likely in our garden to get end rot. Cherries are the least likely. Ask your seed or start supplier before you buy!

^Updated: July, 2017: We’ve recently learned that scientific research is showing that calcium deficiency may not be the cause of blossom end rot. These studies indicate that this problem may be due to environmental stresses like watering, light, and other challenges. And, as we often see, the findings indicate that the problem will likely turn itself around following the demise of the first few fruits to ripen on your plants — whether you add calcium or not. That being said, if your soil is deficient in calcium, adding it as we describe has proven to turn our crops around quickly, and keeping balanced soil nutrition year over year seems to help our plants avoid getting the problem at all.

*Some squash, like bottle gourds, have flowers that open in the evening.


  1. […] Blossom End Rot & Poor Pollination Solutions […]

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  3. Sheila Dye says:

    Why are my many! Tomatoes not ripening?

  4. Sheila, your tomatoes should start ripening as they mature. That being said, without knowing the details, it’s hard to help explain why they aren’t. If it helps, here in the PacNW, our cherries have been ripening for several weeks. But, our larger varieties that were seeded at the same time as the cherries, are still green. Different varieties and sizes take different lengths of time to ripen. Too, location and weather can certainly play a role as well. It’s still July. In most growing locations, there’s still time for them to ripen before cold weather returns.

  5. Can you eat underpollinated butternut squash?

  6. Edwina, thanks for writing in. If the under-pollinated fruit hasn’t rotted, it should still be edible. Not much to them though.

  7. […] further help distinguishing between poor pollination and blossom end rot, I turned to the Garden Mentors (Robin Haglund).  She has helpful photos of these the two cause of problems, and these […]

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(Qualifying purchases made through affiliate &/or sponsored links on this page and others on this site pay a small percentage to Garden Mentors.)