Fickle Weather and Tomato Blossom End Rot

It seems like it’s taken forever to get a good supply of tomatoes coming in from the garden.  It’s not that we didn’t start them early enough in the spring.  It’s not because we transplanted them outdoors too late. It’s not because we didn’t feed them or fuss over them.  Maybe it’s just because they’re awaited with So.  Much.  Anticipation.

Luckily, the adage that good things come to those who wait has yet to been proven untrue in my life or in the garden.  But it had been such a very frustrating wait.  I can only write about it now because I’ve finally been feasting on plenty of fresh garden tomatoes for several weeks now.

You see, the garden was absolutely dripping with beautiful green tomatoes through much of May and June.  I’d  thrill at the first sign of a pinkish blush on whatever parts of them were exposed to the most sunshine.  I’d check them every few days, feeling the firmness of their skin begin to yield a bit more under my fingers each day, sometimes gently pulling against the vine to see if they were ready to let go.  But then, something bad happened.  After an unusually dry June, it rained.  It rained a lot.  And by then, those gorgeous tomatoes I had been pining for largely ended up looking like this:

Blossom end rot on a tomato

Upwards of 80% of the earliest tomatoes in the garden ended up getting these horrid brown-black spots on their undersides that grew and softened as the tomatoes continued to ripen, sometimes consuming more than half the fruit, if I let it get to that point.  More often than not, I would twist off the aborted tomatoes and pitch them into the compost, in the hopes of encouraging further flowering rather than the ripening of ruined fruit.  This is the sorrowful, but not uncommon problem known as blossom end rot.

Blossom end rot can happen to any variety of garden vegetables, including tomatoes, eggplants, and peppers.  It can appear on tomatoes that aren’t the slightest bit ripe, or you may not notice it until you pick a tomato that looks beautiful from eye level, but when turned over, has a big rotted leathery spot on the bottom.  If I’ve noticed one thing, it’s that cherry tomatoes tend to be far less prone to blossom end rot than the larger varieties.  So it’s always best to plant a few cherries to tide you over if you do get a bit of blossom end rot on your other early tomatoes.

Blossom end rot on a Speckled Roman tomato

What causes the problem?  Well, it’s not a parasite, and it’s not a fungus, so you’ll be relieved to know that it can’t be transmitted between various plants in the garden like blight, mosaic virus, and fusarium wilt. (Thank goodness!)

In short, anything that inhibits the supply of adequate amounts of water (or calcium) to the developing tomatoes can cause blossom end rot.  Often, young lush plants that are growing quickly then exposed to dry conditions will have blossom end rot on their first crop of tomatoes, but the problem will usually go away as the plant adjusts to the less-than-ideal conditions. (This is what happened with mine.)

Poor root development can also make tomato plants susceptible to blossom end rot during stressful environmental conditions.  Transplanting tomatoes out too early into cold soil can negatively impact root development (and thus water and calcium uptake), so you’re not necessarily doing yourself a favor by getting your plants out as soon as you deem them safe from those last few overnight frosts.

Some gardeners point to a calcium deficiency in the soil as the cause of blossom end rot, but this is actually rarely a legitimate problem, unless your soil is somehow seriously demineralized.  If you want to be super-cautious about this, there are a few ways to get some extra calcium into your soil:

  1.  Some egg-eating gardeners will save the eggshells from their cooking, toss them into a blender (when dried) and then add a bit of the resulting powder when transplanting their tomato starts outdoors in the spring.
  2. Bone meal.  Plenty of calcium.  Optimally ethical and safe?  That’s definitely up for debate.  I used it briefly back when I started out gardening, mostly because that’s just what was prominently available.  Personally, I greatly prefer (and recommend) options 1 and 3, and 4 over this one.
  3. Gypsum or dolomite are both mineral-based (rock) solutions to low calcium.  Dolomite will raise the pH of your soil, though, making it less acidic, so do a pH test before adding it to your beds.  Gypsum, on the other hand, will add calcium to the soil without altering the pH drastically.  Another perk of gypsum is that it can help a little bit to soften up difficult soil.  See Walter Reeve’s article on the topic here for more info.
  4. Rock dust.  This stuff can contain a wide range of different minerals which can be used by the plants but also by the microbes in the soil, increasing soil vitality (and thereby plant vitality).  John over at is a big proponent of this stuff, so here’s a video from him talking a bit more about it with Don Weaver.

Other measures that can help save your veggies from blossom end rot:

  • Regular watering during dry weather.  (Drip irrigagion is most efficient.)
  • Mulch around your plants. (Just a couple inches of mulch does wonders for retaining moisture in the soil.)

Summer sunflower and the all-important pollinator


About Ashley in Open Lotus Garden

Organic and biodynamic gardener, writer/editor, lover of nature, animals, and the world.
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3 Responses to Fickle Weather and Tomato Blossom End Rot

  1. I have struggled with blossom end rot, too. This year I found an organic fertilizer with extra calcium, which I hope will help, in addition to the regular watering, a necessity here in Ontario this summer!

  2. Karen says:

    Sorry to hear of your tomato problem. I’m still waiting for mine to start to ripen. Blossom end rot affects apples also.

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