IB4 Fertiliser tablets
NPK 12:6:6:+2
(N-12 : P-6 : K-6 : Mg-2)
 
I can highly recommend this fertiliser.
Most Japanese bonsai professionals use it. You will be able to see it in use in many videos of Japanese bonsai on YouTube.
 
Long-Lasting.
Keeps plants green and verdant since it continuously releases nitrogen.
 
Environmentally-oriented.
Continuous and stable nitrogen release minimizes loss due to leaching or volatilization, eliminating nitrate pollution.
 
I have been using this for a number of years now and I can recommend it for feeding any species of tree. It is easy to apply by just placing is on the soil surface ensuring good contact with the soil or place into a fertiliser basket.
The tablet works with watering and releases nutrients into the soil when you water your trees. It takes the fuss out of trying to remember when you last applied fertiliser. 
Place on trees at the beginning of the growing year and thats all there is to it.
Extra tablets can be applied where and when needed as there is little risk of overdoing it because of its slow release action.
I have also used it in conjunction with other fertilisers such as Bio-Gold and my own organic fertiliser when extra nutrients are required for accelarating growth of developing trees.
 
IB4 NURSERYACE® is a small-sized molded fertilizer developed for nursery plants, flowering trees and shrubs, especially for potted plants.
When NURSERYACE® is applied at the time of planting, it sustains plant growth at the ideal level for an extended period (8 to 12 months), without any phytotoxic damage.
 
Application rate. (These are approximate based on my own experience.)
One tablet is sufficient for a 3-4 inch pot. (75-100cm).
Add 1 extra tablet for each inch (3cm) after that.
The tablets can be cut in half or quarters easily to cater for smaller trees.
Available in
100g pack (±15 tabs)
500g pack (±30 tabs)
1Kg pack (±60 tabs)
2Kg pack (±120 tabs)