Greenhouse Plant Nutrient Problems and Disorders



Greenhouse Plant Nutrient Problems

greenhouse plant nutrient problems Shortages or excesses of one or more plant foods can cause a variety of symptoms, from generally poor growth to vivid colouration of the leaves.

Such imbalances are more likely to occur in greenhouse plants because they are often growing quickly and being fed from a small volume of soil or compost. Also, there is no rain to wash out nutrients that the plants do not use. An excess of a particular nutrient can be harmful in the following ways:

  • It can be directly toxic to plants.
  • It can be taken up by the plant in preference to other nutrients, even though they are present in the soil or compost, and hence cause deficiencies.
  • It can make the general level of salts in the soil or compost too high, which has various detrimental effects.


A pH which is too high or too low can also cause nutrient imbalances. The causes of such problems are difficult to identify and to correct, and only a few of the most common are listed here. The best solution is to avoid them in the first place by careful preparation of the greenhouse border and judicious feeding).


Nitrogen deficiency

Symptoms

Poor growth; leaves turn pale (older leaves first), and sometimes have purplish tints. Almost any greenhouse plant can be affected, and those growing in pots are particularly susceptible.

Treatment

IMMEDIATE: Use a liquid feed.

LONGER TERM:Repot pot-bound plants, or top-dress them with worm compost or organic fertilizers. Mulch plants in borders with grass mowings or well-rotted manure.


Nitrogen surplus

Symptoms

Lush soft growth, especially in low light levels. Foliage produced at the expense of flowers.


Treatment

Keep plants well watered and do not feed them until growth becomes normal.


Magnesium deficiency

Symptoms

Yellowing between leaf veins, on oldest leaves first. Plants exposed to strongest sunlight are often the first affected. Tomatoes are particularly susceptible, but note that the natural aging of the lower leaves gives similar symptoms. Excess potassium makes magnesium unavailable.

Treatment

Reduce the use of comfrey or other high-potassium feed. Foliar feed fortnightly with a 2 per cent solution of 10 per cent Epsom salts.


Iron deficiency

Symptoms

Leaves bleach yellow between the veins, youngest leaves first. Common on acid-loving plants, such as azaleas and camellias. Tomatoes sometimes affected. The problem is usually caused by a high pH which makes iron unavailable.

Treatment

Repot pot plants into acid compost and water them with rain-water if tap water has high pH. Check pH of border soil.


Calcium deficiency

Symptoms

Scorching of leaf margins of lettuce, youngest leaves first. Blossom end rot of tomatoes and peppers (a round brown patch at the bottom of the fruits). These symptoms are usually due to calcium being unavailable to plants, or being unable to move to the young tissues, rather than to any lack of it in the soil or compost. Lack of water, high humidity, excess potassium, or a high salt level in the compost can all contribute to the problem.


High salt level

Symptoms

Poor growth, yellowing of leaves, burning of leaf margins, roots going brown and shrivelling. If the salt level (the concentration of soluble nutrients) in the soil or compost is too high, then plants will take up too many nutrients and not enough water. Seedlings, bulbs, and lettuce are amongst the plants most susceptible to damage. Tomatoes and chrysanthemums are amongst the most tolerant. The effect is worse if the plants are allowed to become dry, and may also be exaggerated if the pH of the soil or compost is very high or very low. Compost ingredients such as manure, worm compost, comfrey, and blood, fish and bone, which contain the most readily available nutrients, have most effect on the salt level.

Treatment

IMMEDIATE: Stop using liquid feeds. Remove any mulches of manure, worm compost, etc. Remove any loose potting compost from plants in pots and repot them in fresh compost. Water plants beyond the saturation point of the soil or compost to leach out excess nutrients.

LONGER TERM: Reduce amounts of nutrient-rich materials added to compost or borders, and check the pH. Flood border soils before planting a new crop, applying 20-30 litres of water per sq m over a period of four to five days. Grow a green manure such as grazing rye over the winter.


Greenhouse Plant Disorders

Lack of moisture in the soil

Symptoms

Dullness of leaves followed by wilting; blossom end rot of tomatoes and peppers.

Prevention

Keep plants well watered at all times, and use a moisture-retentive potting compost. Add organic matter to borders.


Lack of moisture in the air

Symptoms

Leaves may brown or scorch, and fruit remains tiny (especially on tomatoes). Pot plants shed buds and flowers.

Prevention

Spray plants with water in morning and evening.


Waterlogging

Symptoms

Yellowing of leaves, stunted growth; root rots encouraged.

Prevention

Reduce watering. Use well-drained potting compost, and add organic matter to heavy border soils.


High temperatures

Symptoms

Scorch of leaves, often resulting in brown papery patches; tomato fruit may develop hard green areas (greenback). The leaves may curl if the temperature is very high, or fluctuates greatly between cool night temperatures and hot day ones.

Prevention

Ensure adequate ventilation and shading. Damp down the greenhouse in hot weather. Do not strip leaves from tomatoes and expose the fruit; some varieties have resistance to greenback.


Damage from paraffin or gas heaters

Symptoms

Fumes from oil or gas heaters can cause dry brown areas on leaves. The small amount of sulphur dioxide produced when paraffin is burnt can affect sensitive plants such as tomatoes and salvias. Low levels of other pollutants (usually oxides of nitrogen and ethylene) can affect the growth of a wide range of plants, even if there is no visible damage.

Prevention

Burn-premium grade paraffin sold for room and greenhouse heaters. Use a blue-flame rather than a yellow-flame heater if you want a heat output higher than 1kW. Keep the greenhouse ventilated when the heaters are in use. Make sure all gas and paraffin heaters are serviced regularly.

29. November 2010 by Dave Pinkney
Categories: Garden Management, Greenhouse Gardening, Pests and Diseases | Tags: , | Comments Off on Greenhouse Plant Nutrient Problems and Disorders

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