To identify potential deficiencies, you have to look at the leaves.

Iron deficiency

• Discoloration of leaves, with only veins remaining colorful, is a sign of deficiency in iron
• It might be a sign of a chalky soil that prevent the correct iron absorption necessary to the production of chlorophyll
• You will need to add a solution enriched in iron and copper

Calcium deficiency

• The apparition of yellowish/brownish stains on the leaves is a sign of deficiency in calcium
• This will slow down the growth of your bonsai tree and will completely prevent the flowering
• You will need to add a solution enriched in calcium and magnesium

Nitrogen deficiency

• Leaves will appear extremely light in color
• You will need to add a fertilizer enriched in nitrogen (fertilizer)

Phosphorus deficiency

• If your tree is too sensitive to outside conditions (dehydration, frost, diseases, etc.), it might be a sign of deficiency in phosphorus
• You will need to add a fertilizer enriched in phosphorus