Blossom End Rot Q&A

When is the right time to start adding calcium/magnesium to your watering regime?
Start using it every 7-10 days once your plants start flowering.

I was really good about watering my tomatoes after the fruit appeared, so why did I get blossom end rot?
Blossom End Rot (BER) is a symptom of calcium deficiency. Calcium is needed for the entire life cycle of fruit development, which includes the moments immediately following a flower being pollinated and fertilized. Since we don’t know the exact moment of fertilization, our job is to just make sure it’s there for when the plant needs it. If there is no calcium from the time they are flowering, the cells might not develop and it paves the way for BER later on in the plant’s life.

Can I fix or reverse Blossom End Rot?
No. There is no going backwards. All you can do is toss the fruit and learn to do something different the next time around.

Do I have to use bottled Cal/Mag or CalMax?
Yes, if you are growing in a pot. There are a few ways to prepare your plant’s growing environment to remove the need for calcium supplementation. A healthy growing medium (soil) that includes finished compost and/or worm casting helps a lot, as will slow-release fertilizer granules. If you are growing in pots, use a supplement. If you are growing directly in the ground at a farm or acreage, there is likely ample calcium in the soil naturally because our soil nutrients formed when this part of the globe was the bottom of an ocean filled with coral reefs, which are made of calcium. So all those beautiful Rocky Mountains are rich in lime, a form of bio-available calcium.

Can’t I just add eggshells?
No. You’d be doing yourself and your plants a disservice if you do. The calcium in eggshells is not water-soluble, which means it is not available for plants to absorb and use. Calcium in eggshells is CaCO3 or calcium carbonate, but plants need it in the form of the calcium ion Ca2+. On top of that, the natural nitrogen cycle of the soil means that mother nature gives nutrient access to decaying things before making them available for growing things. If you put shells in your soil, they’ll decompose and it will reduce the amount of nutrients available for your plant!

Is calcium just for tomatoes?
No. Calcium deficiency shows up under different names in lots of plants:

  • Apple – bitter pit
  • Brussels Sprouts – browning of leaves
  • Cabbage – tipburn
  • Carrots – cavity spot
  • Celery – black heart
  • Eggplant -blossom end rot
  • Lettuce – tipburn
  • Pepper – blossom end rot
  • Tomato – blossom end rot
  • Watermelon – blossom end rot