Green Hong Kong Campaign - Greening Knowledge

Water is one of the four essential factors for healthy plant growths. If a plant does not have sufficient water supply, it will wither gradually. The plant will die after prolonged lack of water. Overwatering will also impede normal plant growth. If the soil is water-logged, a plant may die due to suffocation of its roots. Watering should be conducted appropriately according to plant species and the environmental conditions.

The frequency of irrigation and amount of water given depend on various factors, including -

Type of plant

Whether they are of terrestrial, epiphytic, aquatic, evergreen, deciduous types, cactus or succulent plants ?

Generally speaking, broad-leaved evergreen species need more water while aquatic plants do not.

Size of plant
Seasonal growth habit of plants

Plants need minimal water during their dormant periods. For ornamental shrubs, watering should be kept to a minimum before flowering.
Season and weather

Apart from heavy rain, temperature and humidity are the predominant growth factors.
Growth environment

Exposure of plants to wind and blazing sun will accelerate the evaporation of water from soil and the rate of plant transpiration.
The structure of planting medium

The ability to hold water varies with different structures of planting medium. In general, the larger the granules, the lower the ability to hold water.

There is no pre-determined watering schedule but it is better to water the plant before the plant starts to wither. A major principle of watering is to keep the soil moist. In the case of natural soil, it will dry out and need watering when the soil turns lighter in colour, sandy soil becomes loose or the clay soil becomes firm. The amount of water required is about 15% of the soil volume.

Be careful to keep water off the foliage of hairy-leaved indoor potted plants. We may put the potted plant on a pan and then add in water, allowing the planting material to absorb water through the holes at the bottom of the container until it is wet through. This method is commonly used for African violets.


Fertilizing Most plants have their growth season and dormant period every year. The growth period usually begins in spring. When the weather gets warmer and the raining season is coming, plants begin to produce buds, shoots and leaves and grow up. Plants demand greatly on nutrients for their intense growth. When it is getting cooler, the plants become dormant. They will slow down metabolism and gradually reduce their nutrient requirement. During the growth period of plants, feeding of nitrogen-rich fertilizer is essential to enhance the growth of branches and leaves. Supply of potassium elements could be lessened. When the branches and leaves have grown to an optimum size, nitrogen-rich fertilization can be reduced and fertilizers with equal portion of potassium and nitrogen can then be applied. Otherwise, there will be overgrown branches and leaves with less flowers and fruits. When there are flowering buds, feeding of potassium-rich fertilizer can stimulate the growth of high quality flowers and fruits. Fertilization is not required for dormant plants. Feeding of fertilizers should be made through base dressing and post-plant fertilizing.
	Base dressing While preparing the flower bed and the potting mixture, a small amount of compost should be placed at the bottom mingled with the planting material before planting. Post-plant fertilizing When plants have been growing steadily for three to four weeks, replenishment is required as nitrogen content of the base dressing has almost been absorbed by the plants or lost through leaching. Post-plant fertilizing means the replenishment of fertilizer. Generally speaking, feeding of fertilizers once every four weeks is sufficient.
Scarification Watering will harden the topsoil, adversely affecting the penetration of water into soil and soil aeration. The topsoil should therefore be scarified with a fork weekly. As a general principle, the topsoil should only scarified to such a depth which will not cause injury to the root system of plants. Weeding Weeds compete with crops for sunlight, nutrients, water and space for growth. They are also the vector for the transmission of pests and diseases. Hence, weeds should be eradicated with roots as soon as possible to prevent their growth of flowers and seeds.

Pruning

The objective of pruning is to remove unwanted branches, stems, leaves, blossoms and buds so as to enhance the growth of plants. Appropriate pruning can achieve the following results -

Simulate the germination of lateral buds for more bushy plant growth -

The tips of seedlings should be trimmed off or topped. The branches could also be cut shorter to stimulate the germination of lateral buds. It is commonly used in the propagation of flowers and small shrubs.

Enlarge the size of flowers and fruits (resulting in fewer flowers and fruits) -

Some blossoms should be removed so that the remaining ones can fully utilize all the nutrients. This method is commonly used in the propagation of chrysanthemums and other seasonal container flowers.

Enrich the number of flowers grown -

This method is applicable to the flowers grown on shoots of shrubs, such as roses, allamanda, jasmines, etc.. When the weather gets warm, two-third of the branches should be trimmed off to stimulate the germination of hidden buds and the growth of thick branches.
Improve plant shape and ventilation -

The dense and interlacing stems should be pruned for better ventilation and light penetration. Lateral shoots, if too long, could be cut to maintain a better shape of the plants.

Control the spread of pests and diseases -

Dead or diseased parts of the plant should be removed to prevent the spread of pests and diseases.
Topiary -

Plants can be pruned into certain shapes or hedges. Bushy species are more suitable for this purpose.

Rejuvenation -

Cutting off the old branches and let lateral shoots to develop into main branches.

Let plants with a damaged root system recover gradually -

Plants with a damaged root system have difficulties in absorbing water and will wither. Under such circumstance, some branches should be cut off so as to reduce the plant's transpiration and let the plant recover gradually.

Tools used for pruning must be sharp to make a smooth cut which will minimize infection by pest and disease.