Tomato Plant Not Flowering: Causes and Fixes

Temperature is the most critical factor in tomato flower initiation and fruit set in the UK. Horticulture Magazine confirms that tomatoes need night temperatures above 10°C to retain their flowers. Below this, flowers drop before they can be pollinated. In early UK springs, even plants in unheated greenhouses or polytunnels routinely experience night temperatures below 10°C into May. At the other extreme, daytime temperatures above 30°C — common in unventilated UK polytunnels in summer — cause pollen to clump and become non-viable, so flowers appear and drop without setting fruit. The optimal range for tomato flowering and fruit set is 18–26°C during the day and 13–18°C at night.

Stop it coming back:Most UK tomato growers sow seeds indoors in late March and do not move plants to cold greenhouses or outdoors until late May. This gives the best chance of flowering in warm conditions.

move tomatoes outside permanently before the last UK frost risk has passed — in most UK regions this is mid-May at the earliest, later in Scotland and northern England.

Tomatoes that receive too much nitrogen — from general-purpose fertilisers, fresh compost or farmyard manure — put their energy into producing leaves and stems rather than flowers. This is one of the most common watering and nutrient problems with UK kitchen garden tomatoes. Horticulture Magazine and the RHS both highlight excess nitrogen as a key cause of non-fruiting in tomatoes. The solution is straightforward: once the first flower truss appears, switch to a high-potassium tomato fertiliser (such as a proprietary liquid tomato feed based on sulphate of potash) and stop all nitrogen-rich feeds.

use general-purpose fertiliser or lawn feed on tomatoes — the nitrogen drives leafy growth at the expense of flowering.

Tomatoes are self-fertile — each flower contains both male and female parts and can be pollinated by its own pollen — but they need some agitation to release pollen from the anthers and transfer it to the stigma. Outdoors, wind and bumblebee vibration provide this naturally. Inside an unventilated greenhouse or polytunnel, with no air movement and few insects, flowers remain unpollinated and drop. She Grows Veg and Horticulture Magazine both identify poor pollination as a leading cause of flowers failing to set fruit in UK greenhouse tomatoes. Even a few minutes of hand-vibrating the flower trusses each day makes a significant difference.

assume fruit will set on its own in a closed, poorly ventilated greenhouse — tomatoes almost always need active pollination assistance in enclosed UK growing spaces.

Consistent, even moisture is essential for tomato flowering and fruit development. Plants that experience repeated wet-dry cycles — common in pots and growing bags in UK summers — drop flowers before they can set. Seed Parade's guide to UK tomato growing notes that a lack of water is one of the main causes of blossom drop. In addition, severe drought stress causes blossom end rot (dark, sunken patches at the fruit tip) from calcium deficiency caused by interrupted water uptake, not from a lack of calcium in the soil.

overwater to compensate for previous drought — going from very dry to very wet causes fruit splitting, root damage and nutrient uptake problems.

Tomato plants need to reach a certain size and maturity before they begin to initiate flower trusses. Indeterminate (cordon) varieties typically produce their first flower truss after the plant has formed eight to twelve leaves. A plant that is still establishing after transplanting, or one that experienced a cold check in growth, may not yet have reached this threshold. This is especially common when gardeners sow seeds too early in very low light conditions and end up with weak, drawn seedlings that take much longer to reach flowering size.

sow tomato seeds before late March in the UK unless you have a heated propagator and supplementary grow lighting — plants sown too early in low light produce weak, unproductive seedlings.

Tomatoes are one of the most light-demanding vegetables grown in UK gardens. They require at least six to eight hours of direct sun daily to produce the energy needed for flower initiation and fruit development. Plants grown in partial shade, in an area that has become more shaded as surrounding trees have grown, or on a north-facing wall may produce abundant leafy growth but few or no flowers. Insufficient light also causes etiolation — the long, thin, reaching growth that is a clear indicator of the problem.

expect outdoor tomatoes to produce well in less than six hours of direct sun — cherry varieties are slightly more tolerant of lower light but no tomato does well in real shade.