Blossom-end rot (BER) is a common tomato problem associated with growing conditions — BER affects the tomato fruit. Stems and leaves will show no symptoms—the rot only directly affects the fruit. The bottom side of a tomato that has rot develops a sunken, dark brown, or black spot. You’ll notice BER when the fruit is about half its full size.

Blossom-end rot can’t be reversed on a tomato once it’s taken hold, but you can take these steps to stop the rot in the first place:

• Plant in places with good drainage—pooling water can contribute to tomato rot and other diseases.
• Avoid planting too early in the season—exposing your tomato plants to cooler temperatures and cold soil can ultimately lead to tomato rot. Allow your outside soil to warm up before planting.
• Ensure your tomato plants have good root systems that are strong and deep by mixing compost and organic matter into your soil before planting.
• Use quick-release lime when planting tomatoes, so that there’s plenty of calcium in the soil. Tomatoes grow best when the soil pH is about 6.5.
• Keep your water supply for your tomato plants even throughout the season so that the calcium level is consistent.
• Ensure the right moisture levels by mulching your tomato plants once they’ve been planted and start growing.
• Apply tomato fertilizer that is high in phosphorus once plant blossoms emerge. Too much nitrogen can prevent correct calcium levels.

If your plants have suffered tomato rot, here are some remedies to help get your plants healthy again so you can enjoy more tomatoes from your garden:

• Get tomato-rot-affected plants healthy by immediately spraying with a calcium mix that you can make on your own. Mix 1 tablespoon calcium chloride in 1 gallon of water. Spray directly on plants in the early morning when it’s cooler, two to three times a week until the rot is under control.
• Pick and discard tomato-rot-affected fruit to reduce stress on plants, allowing healthier tomato fruit to thrive.
• Cut out the rot on harvested fruit and eat the remaining good part. Tomato rot doesn’t mean the entire tomato is worthless.