I had the pleasure of helping some friends set up their first no-dig garden this summer. About half of their acreage was devoted to tomatoes, a popular summer treat. My friends regularly sent me updated photos of the progress as they eagerly waited to try their first tomato. One day in midsummer I received a desperate text message that something was wrong. The first green tomatoes all developed dark brown spots on the underside! I immediately spotted the problem in the photos my friends shared: flower end rot.
Blossom end rot (BER) is a daunting sign for novice and experienced gardeners alike. Unlike many other garden problems, this ailment is not caused by pests or diseases and can be reversible. Blossom end rot affects many plants and most commonly affects tomatoes, peppers, eggplants, and melons.
Many gardeners believe that BER is a problem caused by a lack of calcium in plants. However, there are several factors that can prevent a plant from absorbing calcium effectively. My friend's gardening story had a happy ending as we were able to identify and fix the problem immediately so they had few victims at the start of the growing season. In this article we will look at the causes of flower end rot, how to tackle the problem at the beginning and ultimately how to prevent BER in the first place.
What is flower end rot?
Blossom end rot on an unripe tomato. Source: mustard green
Blossom end rot is a physiological disorder that occurs in some fruit plants when the plants are under certain stressors. It affects the unripe and developing fruits of many commonly grown vegetables. BER is characterized by cell death at the end of the flower or at the bottom of the fruit. This can result in partial blackening and drying of the fruit and a visible brown lesion. It is devastating for both home gardeners and commercial growers as this disease makes the affected fruit inedible.
Blossom end rot life cycle
In the case of fruits of nightshade plants (tomatoes, aubergines, etc.), blossom end rot occurs first as water-soaked spots on the bottom of the developing fruit. Blossom end rot can begin two weeks after fruit set and often affects the first fruits to form on the plant. In pepper plants, the stain can also start on the side of the fruit. Eventually, the stain enlarges and the fruit becomes more susceptible to additional damage from insects, fungi, and bacteria. Blossom end rot shows a similar course in pumpkins such as cucumbers, squash and watermelon.
Symptoms of flower end rot
BER can look like dark rot or, based on fruit, can look like sunburn. Source: Oregon State University
Blossom end rot symptoms are manifested in the tell-tale signs of a blackened, shriveled, and leathery appearance at the bottom of the fruit. It could even spread to half of the fruit. Usually, multiple fruits of the same plant will show symptoms as it is a condition that affects the entire plant. In pumpkins such as melons and gourds, flower end rot can resemble a natural break-off of an unpolluted female flower. BER can be confused with sunburn, but sunburn typically manifests itself as a pale leathery patch on tomatoes and peppers, where the fruits are most exposed to the sun.
Causes of Blossom End Rot
Most scientific studies have identified calcium deficiency in plants as the main cause of BER. Calcium is an essential nutrient in plants and plays a key role in regulating plasma membrane function and cell wall structure. However, studies have shown that even under controlled growth conditions with sufficient calcium in the soil, flower end rot can occur. This leads the researchers to believe that the cause of flower end rot is not only insufficient calcium in the growing environment, but also a problem with calcium transport and transpiration through the plant. Adding more calcium to the soil is by no means the best course of action!
Irregular watering is one of the most common causes of flower end rot. Most vegetables are not good at dealing with drought stress. Since calcium is a water-soluble nutrient, the transport of calcium through the plant depends on the plant being able to absorb water at regular intervals through uniform soil moisture.
A Soil pH imbalance can make the calcium insoluble and thus not make it available to the plants.
Apply too much fertilizer, too much nitrogen in particular, can also inhibit the plant's absorption of calcium; this can even include an excess of calcium itself! Too much nitrogen promotes rapid leaf and vine development, which can lead to a calcium deficiency in the developing fruits.
Have high salinity in the soil either through salt runoff, through the location in a coastal region or through saline fertilizers, can also inhibit calcium uptake. Last but not least, the plant transport begins at the roots of the plant.
Root damage can lead to poor nutrient absorption and an overall deficiency in the plant.
Control of the flower end rotation
Eggplants and other nightshades are not immune to BER. Source: Cristynmagnus
BER is reversible when caught early in the growing season. All is not lost! Tomato plants, for example, can be strong producers that produce a lot of fruit during the growing season, and it is almost inevitable that you will lose some to various factors.
After discovering the signs of flower end rot on your fruit, you should immediately pick the affected fruit to prevent the plant from wasting energy as these fruit ripen. Then, review your watering schedule and adjust it to make sure you're maintaining even soil moisture. Mulch around your plants to conserve moisture. Gardeners may find drip irrigation helpful to keep track of watering. If you conclude that watering is not a problem, do a soil test to look for other possible causes of BER. Most of the time you will find that there is enough calcium, but the soil test can reveal other problems such as soil acidity, overfertilization, or soil salinization.
Prevention of flower end rot
The rot can penetrate the bottom of the fruit quite deeply. Source: Mizzou CAFNR
If you know that BER is a problem in your garden, it may be worthwhile to get your soil tested regularly to assess the soil's pH and nutrients. In general, a top dressing with a layer of compost can replenish your soil nutrients sufficiently so that you don't have to add unnecessary chemicals like Epsom salts, calcium chloride, or calcium nitrate to your soil. Adding crumbled eggshells to your soil is another of those folk remedies that has little scientific basis since the calcium in the shells is not immediately available to plants. Similarly, despite what is claimed, a crushed antacid tablet will not fix the problem; it has the same problem as crumbled eggshells.
Since roots are essential to plant health, make sure the plants have healthy and developed root systems. For tomato plants, for example, you can encourage more root growth by burying seedlings deeply at the beginning of their growing season. If root damage occurs due to fungal disease or pest pressure, practice crop rotation or plant a resistant variety to correct the problem
Aside from tackling root health, soil health, and moisture stress, another way to avoid flower end rot is to pick fruits or vegetables that are more tolerant of calcium deficiencies. For example, plum- and pear-shaped tomatoes are more susceptible than round or cherry tomatoes. Tolerant tomato varieties such as Celebrity, Jet Star and Early Girl are easily available in garden centers. With bell peppers, you can try shorter and rounder varieties versus longer, lean varieties.
frequently asked Questions
BER can affect pumpkins like zucchini, as well as other products. Source: avlxyz
Q: Can flower end rot be reversed?
A: Yes, BER can be reversed on a plant and its future fruits, but not on fruits that already have BER. These affected fruits should be picked so that the plant can focus its energy on producing new, healthy fruits.
Q: Is flower end rot caused by overhydration?
A: Overwatering can lead to BER when excess water causes the plant's roots to rot. Damaged roots are unable to update water and other soluble nutrients as effectively, which can lead to BER and even plant death, among other things.
Q: Does Epsom salt help with flower end rot?
A: Adding Epsom salts to the soil or as a spray will not help with flower end rot and can actually make the problem worse. Epsom salt is made up of magnesium sulfate (magnesium, sulfur and oxygen) and does not contain calcium. Therefore, Epsom salt cannot remedy a calcium deficiency in the plant.
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