A brief discussion on the domestication of northern rhododendrons and the techniques of out-of-season flowering

A brief discussion on the domestication of northern rhododendrons and the techniques of out-of-season flowering

Song Dong

Rhododendrons are mostly planted in the open in the south, and the management is more extensive, but in the north, potted plants are needed, and to make them thrive, there are many flowers and colorful colors, and corresponding cultivation management measures should be taken according to their growth habits and needs.

1 Requirements for the environment

1.1 Soil Requirements

The most suitable pH of the soil required for rhododendrons is pH 5 ~ 6, while the soil in northern China is more alkaline, and the acidic soil configuration such as grass charcoal soil or pine needle soil should be selected according to local conditions.

1.2 Temperature Requirements

When the outdoor temperature drops to 10 °C, it should be moved indoors for maintenance, and the minimum should not be lower than 0 °C. In the northern region, it can be maintained outdoors from mid-to-late April to early November. Rhododendron is a semi-negative plant that can cause azaleas to burn in the summer if exposed to the sun for a long time. Therefore, after entering the summer, shade nets should be used, and the light transmittance is 25% to 30%.

1.3 Moisture requirements

The root system of rhododendrons is a shallow root and a slender root group, which is afraid of both drought and waterlogging, and watering should be appropriate and appropriate. Generally, the water holding capacity of the potting soil should not be less than 18%, and if the potting soil is continuously waterlogged for 5 days, the roots will suffocate to death. Watering should be based on rhododendron growth and weather changes, and it should also be noted that the water temperature is close to room temperature, such as tap water should be placed for 1 d.

1.4 Fertilization requirements

Timely fertilization is an important measure for rhododendrons to flourish and colorful flowers, and in principle, master "diligent application and thin application". Rhododendrons avoid thick and raw fertilizer, and excessive fertilizer concentration is easy to burn roots. Rhododendron flowers avoid manure water, should be thinly applied bean cake fertilizer, compound fertilizer, etc., fertilization time is related to rhododendron peanuts for a long time, generally between the long leaves after flowering and between the gestational bud period and before wintering, fertilization is applied 3 to 4 times a year. To prevent yellowing, 0.2% ferrous sulfate can be added to each fertilization application, or if the leaves of rhododendrons are yellowish, 1,000 times liquid ferrous sulfate can also be sprayed on the leaves.

2 Flowering management

2.1 Flowering Management

Rhododendron buds in July-August, in order to make the flowers large and leafy, it is necessary to erase the adventitious buds in time, remove too many buds, and only one bud is retained in one flower branch. After the flower is lost, it should be cut off in time. After the rhododendron flowers are moved to the greenhouse in autumn, they can be maintained at 30 °C for half a month before flowering. If the rhododendron flowers bloom during New Year's Day and Spring Festival, the rhododendrons can be placed in a low temperature chamber of 3 to 4 °C to control the growth rate of the buds. Do not put the buds in the cryogenic chamber when they have flowered to prevent the flowers from frostbite.

2.2 Rejuvenation and flower promotion

Rhododendron flowering period nutrient consumption, indoor viewing lack of sunshine and rain dew moisturization, after the flower need to strengthen management, rapid rejuvenation, promote new branches. Residual flowers and dead leaves should be removed in time, and outdoor light should be gradually increased, but it cannot be moved out of the flower cellar immediately after the flowers are removed, and the growth environment changes are large and easy to cause physiological damage. Proper pruning and shaping, removing weak branches and diseased branches, and cutting off the inner branches can strengthen the ventilation and light transmission within the crown width of rhododendrons.

3 Pest control

3.1 Insect pests

The most common insect pests of rhododendrons are red spiders, short-whiskered mites and so on. Red spiders are mainly harmful in the high temperature of June and August, and like to suck the sap of young leaves, destroy chlorophyll, and make the leaves yellow and fall off. Control can be sprayed with methyl tolbutazine 2,000 times solution, or 3 to 5 baumedo stone sulfur binders can be sprayed during rhododendron dormancy to kill overwintering adults. In the north, 1,000 times of dibromophos can be sprayed in mid-April (stinging period), and 40% trichlorocarcidol 2,000 times or 20% trichlorocarbicide alum 700 times liquid can be sprayed for control in other periods. The above 2 drugs are used interchangeably with stone sulfur compounds, and the effect is better. Short-whiskered mites, also known as leaf mites, are tiny and fine as dust, and are most seriously harmful from July to September every year. Short-whiskered mites like to cluster, often sucking sap near the main vein on the back of the leaf, causing many oily patches to form on the back of the leaf, causing the leaf to fall off. Control methods are to spray 0.5 baumedo stone sulfur compound once in mid- to late October and early spring, or spray 25% amamidine 500 times liquid in mid-to-late October and early spring.

3.2 Diseases

The most common diseases of rhododendrons are powdery mildew, rust, gray spot disease and so on. Powdery mildew and rust can be controlled with 25% powder rust 1 500 times liquid, or with 70% tolbucin 1 000 times liquid. The leaf spots are larger, silvery-grey on the front, and dark brown at the edges, and can be controlled with 70% methyl tolbuzin 1 000 times liquid or with 75% bacillus 600 times liquid.