4 Easy Ways to Prevent the Tomato Rot That Could Ruin Your Harvest

This common tomato disease is easy to avoid once you understand what causes it.

When growing your own tomatoes, one of the most common problems you may encounter is blossom end rot. All seems well while you're watching those tiny fruits grow larger by the day and slowly ripen. But then you notice a soft spot on the bottom side of a tomato that turns black. Blossom end rot has struck. Tomato lovers take heart, this isn't the end of the story. Sure, you may have to toss already affected fruit into your compost pile. But still developing tomatoes on healthy plants can become perfect slicers for your next BLT with these four tips.

blossom-end rot on immature tomatoes on plant
Cameron Sadeghpour

What causes blossom end rot?

The culprit of blossom end rot in tomatoes is not a bug or a disease. This tomato problem, also known as bottom rot, is caused by a lack of calcium brought on by dry conditions. Tomato plants need calcium in all actively growing parts, from the roots to the fruits. Calcium is transported from place to place by water. When water is in short supply, such as during a drought, calcium can't get all the way from the roots to developing fruit so blossom end rot occurs.

Maybe you've heard of calcium-boosting home remedies like planting your tomatoes with antacid tablets or egg shells in the holes to avoid blossom end rot. While these items won't hurt your plants, it's not likely to make much of a difference because most soil has plenty of calcium already. The bigger issue is not enough water to move the calcium to the fruit. However, a soil test will reveal if calcium or other essential plant nutrients are lacking.

The first tomatoes of the season are most susceptible because all parts of the plant are rapidly growing so calcium is in high demand. As the plant moves calcium up from its roots, stems and leaves will use it up first, so occasionally there won't be enough left for the ripening fruit, resulting in black, mushy blossom end rot.

How to Prevent Blossom End Rot

The bright side of blossom end rot is that it's not a disease that spells the end of your much anticipated tomato harvest. It's not contagious; a symptomatic tomato will not "share" the problem with a neighbor. No chemical control, such as fungicide, is effective. This type of tomato rot is simply a condition that usually resolves when your plants get consistent soil moisture. Use these 4 tips to help prevent blossom end rot.

1. Keep tomato plants well watered.

Tomatoes grow best with about an inch of water a week from rainfall or irrigation. Supplement rainfall when needed by watering tomatoes with a soaker hose or a watering can. This is especially important when growing tomatoes in containers, where they tend to dry out faster.

Test Garden Tip: To discourage leaf diseases, avoid getting foliage wet as you water. Yes, rain will obviously get your plants wet, which does help diseases spread. The more you can keep leaves dry, the better.

2. Add mulch around tomato plants.

Spread a 2-inch-thick layer of organic mulch around the base of your plants. Materials such as straw, grass clippings, chopped leaves, or shredded bark all work well. Mulch helps the soil retain moisture, so your plants won't dry out as fast between waterings or rains. Plus, it helps smother weeds.

3. Don't over fertilize.

Too much fertilizer can cause plants to grow faster than they can get calcium to where they need it for healthy growth. Fast growth can lead to blossom end rot. The best way to boost soil nutrients is to add a 2-inch-thick layer of well-decomposed compost to the soil prior to planting in spring. The compost will slowly release nutrients and improve the soil structure at the same time. Only apply fertilizer if recommended by a soil test, and make sure to follow label directions exactly.

4. Care for the roots.

Roots are essential for absorbing the calcium that prevents blossom end rot. Avoid disturbing a tomato plant's root zone so it can absorb maximum calcium. Avoid hoeing and digging in a plant's root zone and keep weeds at bay with a layer of mulch.

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