How to fertilize rhododendrons? Five key points to note

Rhododendron roots are delicate, so fertilizer must be fully composted before use. Generally, fertilizer that has been composted for more than one year and fully fermented is most suitable. When fertilizing, pay attention to the following five key points:

Feed according to the seedling. Seedlings cannot be fertilized; after 4 months, a well-composted, extremely dilute liquid manure may be applied. After the plants are set out and transplanted separately in the following spring, more nitrogen and potassium fertilizer should be applied to speed up vegetative growth. At 2 to 3 years, during the mature stage, more phosphorus fertilizer should be added to achieve a high flowering rate and large, brightly colored flowers. In the old stage, more nitrogen fertilizer may be applied to promote renewal of branches and leaves, rejuvenate the tree, and prolong its lifespan.

Fertilize at the right time. In early spring, from February to March, begin applying a light fertilizer based mainly on nitrogen and potassium to promote sprouting of branches and leaves; April to May is the peak growth and development period, when branches and leaves are luxuriant and roots grow rapidly, so phosphorus fertilizer should be used as the main nutrient, with potassium fertilizer as a supplement, once every 5 days; stop fertilizing during the dormant period of midsummer; in the autumn growth period of August to September, apply dilute phosphorus and potassium fertilizer again, once every 10 days; in early winter, a basal fertilizer such as soybean cake may be applied once.

Apply thin fertilizer sparingly. Rhododendron roots are as fine as hair, and throughout the entire growth process, fertilizing should be done sparingly and lightly. If the amount is too large or the concentration too high, not only can the roots not absorb it, but reverse osmosis may occur, drawing cell sap out of the plant, burning the root hairs, and causing yellow leaves, dried shoot tips, or even death. If this happens, fertilization should be stopped immediately, and water should be applied continuously to dilute the fertilizer solution in an attempt to save the plant.

Use basal fertilizer with caution. For 2- to 3-year-old rhododendrons, in early winter each year, a 3 cm deep trench may be made along the inside of the pot wall, and a small amount of light basal fertilizer mixed from composted poultry and livestock manure and soybean cake may be applied once, then covered with a thin layer of soil, after which it will gradually seep into the soil with watering. Because fertilizer absorbs sunlight and heat and releases heat at night, it also helps the plant grow in winter.

Control water before fertilizing, and water heavily after fertilizing. Before fertilizing, the potting soil should be dry; otherwise, the fertilizer will remain in the muddy soil and cannot spread, and ventilation and water permeability will be blocked, making root rot likely. After fertilizing, water heavily the next morning so the fertilizer fully penetrates and dissolves, which helps the plant absorb it.

It is particularly worth mentioning that rhododendrons like "green manure water." A large vat or cement pool can be used to soak and compost vegetable leaves, green grass, melon rinds, orange peels, rapeseed cake, and so on, covered with plastic film, using sunlight to increase heat and fully ferment and compost them. Then take the upper clear liquid, and add 1/5 green manure water to each normal application of fertilizer solution; the effect is remarkable. Green manure is rich in organic matter, is slightly acidic, and has mild fertility, so it does not harm the root system and can make the plant grow robustly.