If the blossoms of tomatoes suddenly fall off, there are various possible causes. We show you which triggers are responsible for this and what you can do about it.
Flower shedding due to lack of fertilization
Tomatoes have hermaphroditic flowers. Thus, they are able to carry out fertilization independently. For this reason, tomato plants, in principle, do not need insects to take over this part. However, abundant flowering does not guarantee a rich harvest. In order for fertilization to actually take place and tomato fruits to form, a few basic conditions are necessary. If these are missing, the hoped-for harvest will fail to materialize. Inasmuch as the tomato flowers are not pollinated within a few days, they fall off.
Lack of movement
In outdoor tomatoes, the wind moves the flowers so that the pollen comes off and falls on the pistil. However, in closed greenhouses and on the windowsill, there is usually no wind.
In windless locations, you can achieve the movement necessary for pollination by shaking. Often, the shaking caused by stubbing out the shoots is also sufficient.
Lack of insects
While insects are not essential for pollination of tomato flowers, their presence still has a positive effect on the fertilization rate.
To attract bumblebees, bees and co to the tomato patch, flowering plants in the immediate vicinity are perfect. These include:
- Fruit trees and shrubs such as apple, pear, raspberry and blackberry.
- Summer flowers (scented nettle, lavender, sunflower)
- hedge plants such as elder, hawthorn or wild rose
- climbing plants (blue vine, ivy or climbing hydrangea)
- Herbs like St. John’s wort, sage or thyme
Tip: Continuous ventilation in the greenhouse not only promotes the number of pollinating insects, but also lets in the wind that moves the plants
Tomatoes are very sensitive to both extremely hot and dry weather and sudden cold. In this case, the plant discards its flowers to focus on its own survival. Particularly affected here are the so-called old varieties popular with gardeners. Temperatures also play an important role in fertilization. If these are above 20 degrees at night or below 12 degrees, or above 30 degrees during the day, the pollen becomes sticky and is not viable.
Provide balanced culture conditions with moderate temperatures and slightly higher humidity. You can achieve this by shading the greenhouse or outdoor tomatoes. If cool night temperatures are predicted in late spring or early summer, it is best to protect your plants with a film or a so-called tomato house.
Another reason why tomato flowers fall off unfertilized can be too high or too low humidity. If it is too dry, the pollen is not able to stick to the pistil. If the humidity is too high, it sticks strongly and does not detach from the stamens. A relative humidity of between 40 and 70 percent is ideal. It is therefore worthwhile to set up a hygrometer in the greenhouse
Loss of flowers due to lack of nutrients
A balanced supply of nutrients is not only important for the growth and health of the plant, but also for its flowering. Tomatoes are heavy feeders, but too many nutrients are just as harmful as too few.
If the flowers of tomatoes fall off, the cause is often an unfavorable nitrogen content in the soil. If there is too much nitrogen, the tomato will preferentially put its energy into leaf growth and flower formation will only take place to a very limited extent. Too little nitrogen leads to thin shoots that are not able to adequately supply the fruit.
If numerous tomato flowers suddenly fall off, a lack of phosphorus may also be responsible. You can easily recognize a phosphorus deficiency if you take a closer look at the leaves of the plants. If there is bluish to purple discoloration on the foliage, there is a high probability that the plant is lacking phosphorus.
The cause of tomato blossom drop and brown spots on the fruit can also be so-called blossom end rot. Blossom end rot is not a disease, but a deficiency symptom. The tomato lacks the nutrient potassium.
Countermeasures for nutrient deficiency
If the blossoms are already falling, rock flour that you work into the soil at the root ball will help. However, it is better to work plenty of mature compost into the future tomato bed in the spring so that there is no undersupply in the first place. As a rule of thumb, per square meter or plant:
- 3 l mature compost
- 150 g horn shavings or horn meal
- a handful of rock flour
To avoid stress for the plant, the root ball should always be slightly moist. It is also important that the roots have enough space. If the plants are too close together or in a cramped pot, the supply of water and nutrients is limited. The first sign of an undersupply of water is that the leaves curl up and the flowers fall off. Later, stunting of the entire plant may occur.
- Minimum distance: 60 to 100 cm
- Tub size: at least 20 liters per plant.
Note: When watering, be careful not to wet the leaves. A layer of mulch will protect against excessive evaporation
In tomatoes, diseases or pests that cause the flowers to fall off occur from time to time. However, in most cases, not only the tomato flowers, but the whole plant is affected. These include, for example, blight or powdery mildew. However, there is a bacterium that exclusively affects the tomato flowers. Xanthomas bacterium occurs preferably in damp, cool summers. The infection can be recognized by the following characteristics:
- black-gray, dead flower
- yellow transition to the stalk
Once the tomato plant is infected, hardly any remedy will help. Therefore, it is important to ensure optimal site conditions in advance. This includes sufficient distance so that the leaves can always dry well. The best way to protect your tomatoes against disease is to plant them in a tomato house.
Frequently asked questions
Which tomato varieties are particularly hardy?
Less susceptible to diseases and heat or cold stress are so-called outdoor tomatoes. They are not only resistant to blight, but also very weather tolerant. These include: ‘Black Plum’, ‘Golden Currant’, ‘Lily of the Valley’ and ‘Sparta’.
How and when should I shake the tomatoes?
If flowers have already been on the plant for a few days, grasp the stem at the bottom with your hand and gently shake it. The chances of fertilization are best on a sunny day around midday. Since not all flowers ripen at the same time, you need to repeat the process every few days.