Alright I admit it!, when I first became aware of bonsai in the mid 1970's I, like a lot of beginners thought that the mystique of bonsai was in keeping them just this side of dead. One of the things that never occurred to me was to feed them, believing that they would get all the nutrients they needed when repotted into fresh soil. Needless to say that not many of those trees are still around.

I should point out that you are not feeding the tree to make it grow, you are replacing the nutrients the tree has used because it's growing and that feeding a sick tree is a recipe for disaster. Only feed healthy trees!

When developing a young bonsai, the last thing you want to do is to starve it, adding years to the time it takes to get the tree 'Showable'. As the tree matures you may wish to slow it down a little, you can achieve this by varying the type of feed given, away from high nitrogen feeds, but not the amount.

During the growing season (In the UK it's mid March - early September) your trees should be fed once a fortnight with an appropriate feed for what you are trying to do with the tree. This would be a high Nitrogen feed for developing trees and a more balanced type for mature trees. Bear in mind that trees stop growing and hence absorbing nutrients during the high summer. As the trees begin to slow down towards Autumn feed them once a month. After leaf fall stop feeding the deciduous trees, conifers however will benefit from a couple of feeds over winter.

Indoor bonsai continue to grow throughout the year and should be fed all year.

Now we come to one of the more contentious issues in the Gardening world, Organic, or Man-made feeds. I could fill screen after screen on this matter and all it would do is to confuse (Me). The only advice I have for you is that organic feeds are less likely to burn the roots if overfed, but ultimately either is better than none.

My own preference is for pelleted Chicken manure on those trees not for show and liquid fishmeal in trees which may be shown. You will NOT want to use these on indoor trees so perhaps a feed made from seaweed or a chemical feed.

The three red plastic containers shown here, have pelleted Chicken poo in them, another wonderful fertiliser and when the tree is watered the nutrients flow out over a period.

Feeding repotted trees

Under no circumstances should you feed a newly repotted tree. Doing so may stop the recovery of the roots. Leave the tree at least a month, before starting feeding again.


As I said above, you feed to replace the food a tree has used in growing, however putting to much fertiliser, particularly chemical based, is a sure way to kill your bonsai, it's how some weedkillers work. If you suspect you may have overfed a tree, try to wash as much of the fertiliser out of the soil as you can. You can do this by trickling water through the soil (with a hose) for a few days.

No matter whether the fertiliser you choose is organic, or chemical, it will contain certain chemical elements, Nitrogen, Phosphorus and Potassium are the main three.

Inspection of the container the fertiliser comes in will reveal the chemical breakdown of the contents. The major three are expressed as a ratio such as 10:10:10 N:P:K (K being the symbol for Potassium), this would be a balanced fertiliser, with about the same amounts of all three major chemicals. A 15:8:8 would be high nitrogen and better suited to developing trees, an 8:8:15 is a high Pottasium feed, fed to more mature, or flowering trees. While the ratios may differ depending on the supplier the concept will remain the same.

Nitrogen (N)

Nitrogen promotes the growth of the trees leaves and shoots. An excess of nitrogen is dangerous, causing the the plant develop large, dark leaves and delaying the hardening of the wood. overfeeding nitrogen will also delay the production of blossom . Trees are also prone to diseases such as scab or canker if overfed on nitrogen. A shortage of nitrogen is suggested by the pale colour and poor growth of the leaves.

Phosphorus (P)

Phosphorus encourages the growth of roots and flowers. Unlike nitrogen a plant will not take up more phosphorus than it needs. A shortage of phosphorus is indicated by a reddish tinge to the leaves which also point upwards. Superphosphate, applied at the beginning of summer for about two months, in the correct quantities for bonsai, will improve the blossom.

Potassium (K)

Helps the wood to harden, as well as increasing the roots ability to absorb both nutrients and the water they're dissolved in. The symptoms of a shortage of potassum are brownish flecks and curling edges on the leaves. Unfortunately the leaves will not recover and will have to be removed

Sequestered Iron

Not as such a fertiliser, but important if you keep Azeleas. It helps Calciphobe plants absorb nutients. A couple of doses of Sequestered iron during the growing season will suffice.

Allen. C. Roffey 13:13 29/04/2018