Tomatoes are one of the most-grown vegetables in the United States. I have found that there are lots of things that can go wrong between planting your tomato plant and eating your tomatoes. This guide explains what blossom end rot is and how to prevent it.
What Is Blossom End Rot in Tomatoes?
Blossom end rot is caused by a lack of calcium in the tomato fruit. It is a physiological disorder and is not caused by diseases or pests. However, once blossom end rot starts, mold, fungi, and bacteria may colonize the lesion. In addition, insect pests may start to eat the rotten fruit.
What Does Blossom End Rot in Tomatoes Look Like?
Blossom end rot starts as a small, dry, brown spot on the bottom of the tomato, where the blossom was attached. The skin there is leathery and thickened. The lesion becomes sunken, water-soaked, and slimy as it gets larger. Blossom end rot can damage half of the tomato. Blossom end rot can allow diseases and pests to gain a foothold on the tomato plant, where they can continue to cause problems.
How Calcium Functions in Tomatoes?
It is important to understand how calcium functions in tomatoes to understand blossom end rot. Calcium is brought to the plant tissue by water when the plant transpires, or vents water through its pores on the stem and leaves. The calcium goes to the quickest growing area first, usually foliage and the stems. It goes to the fruit only if there is enough left over. You can have a calcium-rich soil but still get blossom end rot because the plant cannot draw up enough calcium to prevent it.
The Top 5 Causes of Blossom End Rot in Tomatoes
Here are the top causes of blossom end rot in tomatoes.
Inconsistent Soil Moisture
Calcium requires water to move in the plant. Too dry or too wet soils inhibit the movement of water in the plant. Potted plants are more susceptible to blossom end rot because they tend to have more fluctuation in soil moisture. The soil moisture should be kept consistent throughout the life of the tomato plant.
If the roots are damaged, the plant cannot get enough water to move the calcium throughout the fruit. Root damage can be from root rot caused by soil that is too wet. It can also be caused by hoeing too deeply when killing weeds. When hoeing weeds, be careful not to damage the roots. Scraping the surface of the dirt around a tomato plant is usually sufficient to remove the weeds if you weed regularly.
Too Much Nitrogen, Potassium, or Magnesium
Too much nitrogen can cause the foliage to grow out of control. The foliage uses all the available calcium and fruits get blossom end rot. The first fruits of the year often get blossom end rot because the plants are growing a lot then. Too much potassium can make it difficult to take water into the plant, causing a calcium imbalance and blossom end rot. Too much magnesium inhibits the uptake of calcium. Even if your soil has plenty of calcium, the plant cannot take it up and use it. Get a soil test and fertilize accordingly. Use a fertilizer that contains calcium and is formulated for tomatoes.
If the humidity is too high, the evaporation of water from the tomato plant can be interrupted. If the wind is high, too low humidity or too high humidity can make transpiration difficult. If transpiration does not occur, the calcium will not be drawn up into the tomato, and that will cause blossom end rot. If you live where the wind blows often, place a windbreak around your tomatoes. This can be a tall plant like pole beans or a structure. Just make sure the windbreak does not prevent sunlight from reaching the tomato plant for at least six hours a day.
Tomatoes grow best with a pH of 6.0-6.5. Very acidic soil and very alkaline soil make blossom end rot more likely. A soil test will tell you the pH and how to adjust it for your tomatoes.
Treating Blossom End Rot in Tomatoes
There is no treatment for a tomato once it gets blossom end rot. Sprays will not help. Once a particular tomato gets blossom end rot, I immediately pick it. If the damage is slight, I cut the lesion out and eat the rest. Picking the tomato keeps the plant from wasting energy on it and keeps diseases and pests from colonizing it.
Preventing Blossom End Rot in Tomatoes
Since there is no treatment for a tomato with blossom end rot, you need to prevent the tomato from getting it in the first place. Here are my recommendations to help prevent blossom end rot.
Get A Soil Test
I recommend getting a soil test each year. A soil test will tell you how much of each nutrient is in the soil and how much of that is available to your tomato plants. I have seen results where adequate calcium is in the soil, but a high magnesium level or other factors kept it from being available to the plant. The soil test results will also tell you the soil pH. Follow the recommendations in the soil results before planting the tomato plants. Don’t add calcium to the soil unless the recommendations tell you to. I fertilize with the recommended amounts of fertilizer, then work the fertilizer in the top three inches of soil and water the area before I plant.
A soil test will also tell you the soil pH and if you need to amend it. Lime and sulfur take time to change pH, so do a soil test three or four months before you plant tomatoes for the first time in an area and apply the lime or sulfur then. After the first year of planting, you should do a new soil test every year before spring planting.
Manage Soil Moisture
The best way to prevent blossom end rot is to manage soil moisture. You want the soil to be evenly moist. An inexpensive moisture meter can really help with this. Keep the needle in the moist area. Add one inch of water from rain and irrigation a week. If you live in a hot climate, you may have to water twice a week to keep the soil moist. Water at the roots with drip irrigation or a soaker hose. Avoid getting the foliage and tomatoes wet when watering, as it promotes diseases.
The other way to manage soil moisture is to use a raised bed. If the tomato is sitting in a puddle for days after a rain, the roots will be damaged and finally rot. You can’t do anything about lots of rain, but you can make sure you plant where the soil will drain quickly. Adding compost to the soil will help it drain, too. Mix three inches of compost into the top six inches of soil before planting. As a bonus, adding compost will boost your soil fertility. Do not add uncomposted manure to your vegetable garden. Raw manure contains E. coli and other pathogens that can make you sick.
Put three inches of mulch down around the tomato plant, but make sure none actually touches the stem. The mulch helps keep soil moisture and temperature stable and helps keep weeds at bay. As a bonus, it keeps low-hanging tomatoes off the soil. Hardwood chips or clean, weed-free straw are the best mulches to use. If your soil pH is not acidic enough, you can use pine bark and pine straw mulches. While these are not a quick fix and will not make a huge difference, they will not cause a problem, either.
Choose A Resistant Variety
Some tomato varieties are more likely to get blossom end rot than others. Heirloom varieties are often more sensitive to calcium deficiency than other varieties. A study by the Illinois Extension Service found a less than ten percent incidence of blossom end rot even in severe years in the following tomato varieties: Celebrity, Fresh Pak, Jet Star, Manapal, Mountain Proud, Pik Red, Sunny, and Winter. The following tomato varieties they tested have a fifteen to thirty percent incidence of blossom end rot in severe years: Big Boy, Castle King, Fantastic, Independence, Supersonic, Surprise, Whopper, and Wonder Boy.
Elongated plum or pear tomatoes are more susceptible to blossom end rot. These include San Marzano tomatoes. Some Roma-type tomatoes, such as the Gladiator hybrid, are resistant to blossom end rot. There are resistant beef steak tomatoes such as Super Beefsteak hybrid. A resistant cherry tomato hybrid is Mirabelle Blanche. There are other resistant tomato types. Consult your nursery or seed vendor to find the ones that grow best in your area.
Use The Right Fertilizer
Use a fertilizer where the nitrogen is supplied by nitrates instead of ammonium. Make sure any fertilizer you use also has calcium in it. Most fertilizers formulated for tomatoes have calcium in them. Do not over-fertilize. Follow the soil test recommendations before planting and apply fertilizer to replace the nutrients the tomatoes are taking from the soil. Extra fertilizer unbalances the nutrients in the soil and can cause more trouble than it solves. Follow the directions on the label for exactly how to use each fertilizer brand.
If you want to add organic calcium, use powdered eggshells. Crushed eggshells won’t help, so grind them into a powder. Sprinkle the powder around the tomato plants and water the soil well.
Can You Eat Tomatoes with Blossom End Rot?
If the rotted area is small, you can cut it out and eat the rest. However, sometimes the rot is a lot worse inside than it looks from the outside. If you slice into a tomato and it is rotted inside, don’t eat that part.
Some Notes on Growing Tomatoes in Containers and Preventing Blossom End Rot
Potted plants are much more likely to have blossom end rot problems because it is harder to keep the soil moisture constant. Here are some tips to keep from having that problem.
- A moisture meter is even more critical for container tomatoes than in-ground tomatoes.
- Water the tomato when the surface of the soil gets dry if you do not have a moisture meter.
- Indoors, water by placing the pot in a pan and filling the pan with water. This lets the soil absorb as much water as it needs but doesn’t get the foliage wet. Remove the plant from the pan after 15 minutes and let it drip for another 15 minutes before putting the pot back where it belongs.
- If you have tomatoes in containers outdoors, water at the soil level. Don’t get the foliage wet.
- Indoors or out, make sure you place a layer of mulch on the soil so that when you water, the soil isn’t splashed on the foliage or fruit.
- Place the container where it gets morning sun and afternoon shade to keep the soil from getting so hot and drying rapidly.
- You will have to water hanging baskets and other small containers daily if the weather is hot.
Frequently Asked Questions
Should you cut off tomatoes with blossom end rot?
Remove the tomato from the tomato plant as soon as you notice blossom end rot. The lesion will grow, and the plant does not need to put energy into a damaged tomato.
Can I compost tomatoes with blossom end rot?
Yes, you can. Blossom end rot is not contagious so you can compost the tomatoes without contaminating the compost.
Is it too late to add calcium if tomatoes are showing signs of blossom end root?
Most extension agencies say it is. Alabama Extension recommends drenching the soil around your tomatoes with 4 pounds of calcium nitrate or calcium chloride per 100 gallons of water when you find blossom end rot. However, this only helps if your soil is deficient in calcium. If there is adequate soil calcium, this will not help.
Can I use cal-mag for tomato blossom end rot?
If you have a calcium deficiency, you can add calcium this way. However, if the soil is already high in magnesium, you are better off using another form of calcium. Too much magnesium inhibits calcium uptake.
Can you use milk to treat blossom end rot on tomatoes?
Milk does contain calcium, but I would not do this. You are more likely to attract rodents and other animals that will dig up your tomato than cure blossom end rot.
Can you use tums for blossom end rot in tomatoes in pots?
Yes, you can. Crush the tums and sprinkle them on the soil, then water the soil, so the tums are absorbed.
Will picking tomatoes early prevent blossom end rot?
No, it will not.
In conclusion, blossom end rot is caused by a lack of calcium in the tomato. This is most often caused by poor watering practices, but root damage, soil pH, and poor fertilization also cause the problem. Doing a soil test and following the recommendations, planting resistant tomato varieties, keeping the soil evenly moist, mulching around the tomato plants, and using the proper fertilizer can prevent blossom end rot.