How to fertilize the osmanthus trees?

Osmanthus tree is a kind of common garden tree species in southern China. Seedlings also can be cultivated through soilless potted way as long as it is fertilized zinc sulfate monohydrate or zinc sulfate heptahydrate and other water soluble fertilizers. 

Fertilization time: about on every February and August
Compound water soluble fertilizer ingredients: mixed fertilizers mainly contain sulfur fertilizers as magnesium sulfate, borax, zinc sulfate, copper sulfate and ammonium molybdate. 5 grams compound is enough for each pot dosage, which is evenly applied in the matrix.

Effective period: 3-4 months
Advantages: The fertilizer by this solution not only long-term works but slow-released. Besides, this fertilization may also cut the production cost, reduce labor intensity and improve efficiency.