Blossom end rot
Blossom end rot produces dark patches on the bottom of tomato fruits – as well as peppers and aubergines. This plant disorder is mostly caused by irregular watering.
- Roughly circular black or brown patches at the bottom (blossom end) of the fruit
- As they age, the patches may become sunken
What is blossom end rot?
Blossom end rot is not a disease, but a physiological disorder – produced by incorrect growing conditions. It is caused by a lack of the nutrient calcium in the fruit. This causes the cell membranes to break down and the affected cells to die. New cells don’t grow and this results in the formation of the sunken areas.
It is highly unlikely that soils, potting composts and growing-bags don’t contain enough calcium, but its movement within the plant needs a good, regular supply of water to the plant. A lack of water at the roots, or an irregular, non-constant supply of water, prevents calcium movement. The fruit, being the furthest away from the stem, is the first part of the plant to suffer if a lack of water prevents calcium getting to them.
Plants growing in growing-bags and, to a lesser extent large pots, that have limited space for the roots to grow are most at risk. But plants growing in the ground can also be affected.
Blossom end rot can also occur when fertiliser is added to dry soil or compost, because the concentration of nutrients restricts water uptake by the roots. Excess applications of nitrogen-rich fertilisers makes the problem worse.
What does it affect?
How to prevent blossom end rot
Once affected, there is nothing you can do to save the fruit. They should be picked and composted.
Your aim should be to grow the plants as well as possible, so they never go short of water.
The soil or compost should be kept consistently moist, never allowing it to dry out – especially once the fruits begin to form and develop. Try to keep the soil or compost evenly moist, without cycles of drying out followed by flooding. During hot weather, especially for plants growing in containers that restrict their root growth, this may mean watering more than once or twice a day. This is especially important with thin growing-bags, since the small volume of compost dries out very quickly and is often very difficult to re-wet thoroughly once it has dried out.
Automatic watering systems, drip watering systems, growing in larger pots or using giant planters instead of growing-bags will all help to alleviate drying out and wetting/drying cycles.
Covering the soil or compost with a mulch will also help conserve moisture.
Using growing-rings on top of growing-bags and pots provides extra compost, which will help reduce drying out.
Feed with a high-potash tomato fertiliser, which has the right combination of nutrients for stronger, healthy growth – as well as higher yields of tastier fruit. Always make sure you apply it to already moist soil or compost at the recommended dilution rate.
High air humidity can also reduce water uptake by the roots, so good ventilation for greenhouse crops may help reduce problems with blossom end rot.
- Giant planters
- Growing-bag grow rings
- Drip-watering systems
- Automatic watering systems
- Tomato fertiliser