Plant Disorders – Understanding the Problem

Plant Disorders

Plant disorders are problems caused by environmental conditions such as low temperature, day length or herbicide spray drift. They can also result from shortages of particular plant foods; these are known as mineral deficiencies.


Bolting is the term used when a plant flowers prematurely. It can be caused by adverse temperature, day length, root disturbance at transplanting or shortage of water. Bolting is mainly a problern with vegetables that are normally picked before they produce a tough flowering stem. Similar adverse conditions may cause annual flowers to run to seed too quickly without producing a good display.

The following plants are prone to bolting: Beetroot Low temperatures encourage bolting. In beetroot. Choose ‘bolt-resistant’ varieties for early sowings.


bolting celery - plant disorders Low temperatures, root disturbance and water shortage can trigger bolting. Keep young plants at a minimum of 12°C (54°F), even when planted out. Raise plants in modules to avoid root disturbance. Incorporate organic matter into the soil before planting, mulch well and water if necessary.

Chinese cabbage

Low temperatures and increasing day length can trigger bolting. Keep plants at a minimum of 10°C (50°F). Sow at the appropriate time for the variety (check instructions on the seed packet). Many must be sown in midsummer or later to prevent bolting.


Grow in spring and autumn to avoid long days and dry weather that can encourage bolting.

Overwintering onions

Onion varieties for over-wintering will tend to bolt in spring if the plants are too large when winter starts. Follow the recommended timing of sowing or planting precisely.

Poor or no fruit set

Poor pollination will result in a poor crop of fruit, beans, tomatoes, courgettes and other fruiting crops. This may be due to cold, wet and windy weather conditions preventing the work of pollinating insects, frost killing the flowers or lack of pollen.

Providing windbreaks and choosing later-flowering varieties can help to solve the first two problems. Lack of pollen may be due to several causes. With apples, pears, sweet cherries and some plums, another variety of the same fruit, flowering at the same time, is required to provide pollen. In the case of courgettes and other cucurbits, it may be that the pollen-providing male flowers are not open at the same time as the female flowers. This often happens early in the season. If necessary, these flowers can be pollinated by hand if bees are not doing the job adequately.

Water shortage and high temperatures can also reduce fruit set, especially in the case of runner beans and tomatoes.

Poor flowering can be caused by overfeeding and hard pruning, which can encourage a plant to grow vigorously at the expense of flow.- ering. The answer is to stop feeding and alter the pruning regime.

If a large fruit tree is growing too vigorously, sowing grass around it to compete for food can be helpful. Alternatively, the problem may just be lack of flower buds because of inappropriate pruning or perhaps bullfinch damage.

Narrow leaves and distorted growth

Hormone weedkillers can cause distorted growth on tomatoes, cucumbers, cabbages, sprouts and other brassicas, sweet peas, and vines in particular.

This can happen even in a garden where no weedkillers are used. The spray may drift in from another garden, or herbicide residues in straw or grass mowings may be the source. There is no cure.


The presence of small warty growths on stems and the underside of leaves is a condition known as oedema. It occurs mainly on eucalyptus, ivy-leaved pelargoniums, peperomia, camellia and brassicas and vines.

The cause is an excess of water in the plant. Stop watering and new growth should not be affected. In the greenhouse, increase ventilation and restrict watering to the morning only. Removing affected leaves only exacerbates the problem.

Split fruit, vegetables and bark

Splitting of fruit, such as tomatoes, and vegetables such as carrots and cabbages, as well as the bark of trees, is caused by an irregular supply of water. Heavy rain after a drought, for example, will cause very rapid growth which leads to splitting.

Increasing the water-holding capacity of the soil by adding organic matter and mulching are ways of helping to reduce the risk of this disorder occurring.

Frost damage: brown or shrivelled leaves

Sudden browning of leaves overnight of strawberries, potatoes and a wide range of unrelated plants is usually caused by frost. Other signs of frost may not be visible the. Morning after the frost because the worst of the damage is only apparent after a spell of good growing weather.

During cold, frosty weather, valuable plants can be protected overnight with a covering of straw, sacking or horticultural fleece, all of which should be sufficient to protect the plants.

Leaves yellow between veins, bark peels, foliage discoloured and shoots dying back

The above symptoms, which will vary with different type of plant and the severity of the condition, are caused by poor root action due to waterlogging. Plants that regularly suffer from any of these symptoms should be moved to a drier site.

30. January 2011 by Dave Pinkney
Categories: Organic Gardening, Pests and Diseases, Plant Care | Tags: | Comments Off on Plant Disorders – Understanding the Problem


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