While volunteering at Cold Water Gardens in Milton, Florida, I learned about tomato blossom end rot (pictured below)–which is the result of a calcium deficiency. When you see this, there is either a lack of calcium in the soil, or the plant is failing to effectively take up and deliver calcium to its fruits.
And although there is no way to reverse the rot, it can be prevented by:
1. Ensuring soils have the proper pH before planting. *The idea pH for tomatoes is 6.5
Do-It-Yourself soil kits can be purchased relatively cheap, but more can be determined by professional testing. — Your county extension agent can direct you to professional soil testers in your area. The results will come with amendment recommendations based on your soil’s pH reading.
2. Seeding / transplanting at appropriate times.
Planting when it’s excessively hot or cold can damage roots and impair their ability to take up water. (Tomatoes absorb calcium through water).
3. Raking compost and organic matter into the soil before planting.
This will encourage a strong, deep root system.
4. Planting in an area with good drainage.
This will help keep roots healthy.
5. Watering evenly and consistently throughout the season.
–Water heavily a few times a week rather than lightly everyday; this will ensure regular calcium uptake.
6. If using fertilizer, apply only after blooms have emerged, and make sure it has a Nitrogen (N)-Phosphorus (P)-Potassium (K) ratio of 4-12-4 or 5-20-5.
To much Nitrogen, or too much fresh manure can prevent calcium uptake.
IF YOUR PLANTS ARE ALREADY AFFECTED:
*Remove bad fruits so that the plant can direct energy to healthy tomatoes.
*Add a calcium amendment to the soil immediately; Gypsum is a great source.
*Remember that if you cut off the bad spot on the tomato the rest is perfectly edible.