GROWING HOUSE PLANTS UNDER GLASS

Although flowering and non-flowering plants are included in this category, the bulk are evergreen plants, mostly non-flowering ie foliage plants. The large scale production is in the hands of a few specialist nurserymen and there is a steady demand for these plants throughout the year, with a seasonable rise in sales for the pre-rChristmas period.

The easiest to grow are popular because they will do reasonably well in temperatures of near 8 – 10°C and will stand some neglect in watering. They are most tolerant of the varying conditions found in living rooms and dwelling houses.

Where only a limited range of house plants is being produced on a nursery, the following are suited to the temperature ranges mentioned:-

10 – 15°C Ficus pumila – Hedera in variety – Pilea – Tradescantia

15 – 18°C Aphelandra – Sansevieria – Aralia – Rhoicissus – Maranta – Peperomia –

Begonia rex

18 – 21°C Scindapsus – Philodendron.

The difficult subjects like Aphelandra, Anthurium and Begonia rex need the higher temperatures. They are often short lived after purchase, but are useful selling lines. Commonly grown house plants include the following:-

Rhoicissus – Aphelandra – Hedera Chlorophytum – Maranta – Tradescantia – Cissus -Sansevieria.

Although not grown to the same extent as the above, the following are popular:-

Pilea – Peperomia magnolaefolia variegata – Croton – Aralia, (Citrus mitis will probably become popular).

Plants are sold mainly in 85mm pots, some in 125mm pots and a lesser number in 75mm pots. Trays or boxes of mixed plants are usual. Some specialist growers sell direct to florists.

Short Day Plants

Flowering is induced by a day length of 10 hours or less e.g. Poinsettia, Chrysanthemum, Kalanchoe.

Chrysanthemum. This is a plant widely grown commercially as a cut flower and also as a pot Chrysanthemum. A look at this example will show the implications of photoperiodism. Chrysanthemums are grown all the year (AYR Chrysanths) and to achieve this during periods of long day length, the day has to be shortened by using black-outs (woven man-made fibres or black polythene) in the glasshouse in order to manipulate the day length. However, if plants were in their early stages of growth at the commencement of short days, they would be induced to flower before they were well enough developed; in this instance the day length is increased in order to keep plants in a vegetative (non-flowering) state until they are sufficiently well developed. Night break lighting is one of the cheapest ways of achieving this apparent increase in day length.

Photoperiodic effects require light of very low intensity compared with the light required for photosynthetic activity.

The cover may be over individual beds or over the whole glasshouse with a roller blind effect from A to B, with the sides and ends included at the edges of the block.

Humidity may build up under the shading leading to loss of quality in the bloom due to a build-up of botrytis.

High light intensity and lower temperatures produce short sturdier plants. Many plants instead of being tall will be bushy and have shorter internodes. Poor light levels with higher temperatures cause long tall growth and plants with long internodes. This is very often described as being etiolated.

Light wavelengths

Light energy is provided in discrete units called PHOTONS, each of which carries one QUANTUM of energy. Light for photosynthesis needs to be in the 400 to 700 NM wavelenth range.

Photoperiodism

This term relates to the plant response to the daily periods of light and dark. The length of the day influences a hormone and the response to that in the growing tips of the plants induces or inhibits flower bud formation. Plants can be divided into three response categories: short day plants, long day plants and day neutral plants.

In modern cropping programmes night-break lighting and darkening screens are used to control times of flower and vegetative development. With these methods a crop such as chrysanthemums may be timed for a particular flowering date to meet a special market.

Night-break lighting is operated by time-switches which are controlled by computer. This lighting is given in the middle of the night to interrupt the dark period and where chrysanthemums are concerned it inhibits flowering. In long days if dark sheets are used as screens and automatically drawn over the crop in late afternoon, the resultant artificially shortened day will result in inducing the plant to flower.

a) Dav Neutral Plants (Light Indifferent Plants)

Plants which flower under a wide range of day lengths are termed day-neutral plants, meaning that the length of day has no great effect on flowering eg Pelargonium, Pansy (Viola sp).

b) Long Dav Plants

Flowering here is induced by long periods of day length I.e. 14 hours or more e.g. the majority of summer flowering plants e.g. Antirrhinum, Petunia and the garden pea.

DAY LENGTH

The influence of day length on cultural practices

When day length noticeably shortens during the autumn, plant growth slows down; this day length shortening is accompanied by a fall in temperature. There is a close link between light and temperature with regard to plant growth and the shorter the day, the less photosynthetic activity.

The work of potting up or potting on plants is generally best carried out during periods of good light or when day length is increasing. These tasks should therefore virtually cease during the months of low light I.e. November – February because plants are not in an actively growing state and are unable to exploit the fresh compost provided for them.

With regard to glasshouse growing, all possible practicable means should be carried out to lessen the effects of poor winter light.

The following affect the amount of light entering the glasshouse

a) Cleanliness of glass.

b) Amount of constructional materials in the glasshouse.

c) The shape of the glasshouse, ie the nearer to a hemispherical shape the better.

d) Orientation. For larger glasshouses standing on their own, E-W orientation is best for maximum winter light. This is because it places the glasshouse at a more favourable angle to receive the sun’s rays ie sides and roof of glasshouse admit light better than a gable end.

Supplementary lighting can be given to plants to help overcome the poor quality winter light. This can be produced by:-

a) Mercury vapour lamps.

b) Low pressure sodium lamps.

c) Fluorescent lighting can be used but there should be an awareness that they will block out natural daylight when not in use. Also the wavelength of the light produced is different from natural daylight. The majority of plants will grow more rapidly if one provides additional heat but if the length of day is short, the provision of this additional heat will be of less value to plant growth.

1. Osmocote Plus 15N + 8P205 + 11K20 + 2MgO + tr 12-14 months.

Dibbled during potting at a rate of 5 grams per litre. This way 90% of the fertilisation of the whole cultivation period is secured.

2. Osmocote Plus 15N + 10P2O5 + 12K20 + 2MgO + tr 5-6 months.

Dibbled during potting at a rate of 3 grams per litre or 3 Kg per cubic metre. tr = trace elements

These plants will need a second CRF application early in the next growing season. Depending on the grower’s practice this can be done either by topdressing 3 grams of Osmocote Plus 15N + 10P2O5 + 12K20 + 2MgO + tr 5-6 months (the period over which the nutrients are released) or by application of Osmocote Plus Tablets with the same longevity. Because of different pot sizes, these tablets are available now in 5g and 7.5g.

REMARKS

Research in Belgium showed that the optimal temperature in winter lies in this type of culture around 12°C and shouid not exceed 16°C. The same study also advises growers to keep their plants a little more moist, compared with soluble fertiliser practice.

The plants were potted in peat based substrate; pH adjusted and mixed with 300 grams of Micromax per M2.

The following is an extract from a publicity leaflet for a particular OSMOCOTE, a slow release (or Controlled Release Fertiliser). Extract from SIERRA INFO – the producers of OSMOCOTE.

Azalea and Erica

Growing Azaleas and Ericas with controlled release fertilisers has been the subject of a three year long trial period in various countries and on different nurseries. During an excursion in August 1988, specialists and sales people from Germany, the Netherlands and Belgium visited trials in Germany and Belgium. The very positive results of the different trials justify the conclusion that CRF offer growers an excellent system to grow Azaleas and Ericas.

Azalea

BENEFITS

This nutrition system delivers a high nutrient input, combined with low salt levels. It reduces the need for soluble fertilisers by almost 80%. This is extremely important because traditionally these cultures are located in sandy areas, where groundwater pollution is becoming more and more of a problem. In fact, although trials regarding rate and time of application are still going on, some growers consider the benefits showing already in trials, justify the commercial use of CRF now.

Azalea

The traditional Azalea culture starts with the potting of rooted cuttings in summertime. After overwintering in cold glasshouses, these plants are the next year transferred outside to the field and are ready for sale in autumn. Depending on the grower’s practice, the fertilisation of this culture with CRF is possible in two different ways.

c) Foliar Feed (a liquid feed applied to the foliage)

This gives a very quick response and is useful for correcting plant nutrient deficiencies e.g. Magnesium deficiency of tomatoes corrected by Epsom Salts (Magnesium Sulphate).

N.B. Liquid feeding should not be carried out whilst compost is dry, excessive feeding should be avoided, care must be taken to avoid splashing hairy leafed plants e.g. Saintpaulia and generally less feeding is carried out during dull cool conditions I.e. periods of less active growth.

d) Slow Release Fertiliser

Usually mixed with the compost.

Commercially the majority of plant feeding in containers is carried out by slow release fertilisers. Also called controlled released fertilisers (C.R.F.).

Definition

The term slow release fertiliser could be given to any fertiliser which releases its nutrients slowly eg the organic fertiliser bonemeal. However, it usually refers to an inorganic, granular resin coated fertiliser of which the trade names end in ‘cote’ e.g. Osmocote, Ficote.

THE ADVANTAGES OF SLOW RELEASE FERTILISERS

a) Nutrient release is governed by temperature ie the higher the temperature, the more active the plant growth and therefore the greater demands on nutrients. The resin coating will break down more quickly in warmer conditions.

b) There is less leaching of nutrients.

c) Nutrients are available over a long period; different formula types are available and these may release their nutrients over differing lengths of time e.g. 1 to 2 months, 3 to 6 months, 6 to 9 months.

d) There is less danger of over-feeding.

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