Another common bonsai myth is that sick or recovering plants, or newly transplanted bonsai should not be fertilized. The analogy is that it will over feed the patient or is the equivalent of over dosing with vitamins. I think the proper analogy should be that feeding at half strength or not all is analogous to not taking your medicine, vitamins and nutrition when you are sick.
The recommended strength is designed to produce a soil solution of fertilizer salts at a specific range of electrical conductivity. In this range it is very easy for plants to pick up the various N,P, and K ions. It doesn't matter if the plant is a seedling, newly rooted cutting, newly root pruned bonsai, or recovering plant. They all will pick up nutrients more easily if fed in this range.
Roots are roots. Probably the most tender roots you will ever come across are the newly formed adventitious roots on a cutting. These are very fleshy and extremely fragile. I have fertilized my newly rooted cuttings (and seedlings) for years with full strength soluble fertilizers and they have all thrived. In fact, they quickly show chlorosis if I don't feed them at this level.
There is no evidence of which I am aware that fertilizer will interfere with the process of regeneration of roots. The belief that fertilizer 'burns' young and tender roots cannot be substantiated. Fertilizer is necessary for the health and growth of roots as well as foliage. If new roots cannot find fertilizer from the soil solution, the plant will rob nutrients from existing tissues to fuel new growth. This doesn't sound like a formula for recovery to me.
Research has shown that new roots are often found encasing beads or chunks of pure solid fertilizer. If there were a problem with localized 'burning', there would be a 'dead zone' around such chunks, not fresh new roots. I am not arguing for more fertilizer here, just the continuation of a reasonable fertilizer schedule. Over fertilizing causes a whole new set of problems.
It is my experience that it is important to get a plant back into good growing conditions as soon as possible following transplantation, root pruning, or a root problem. Allowing a plant to languish in the dark without food may relieve light and temperature stress, but does nothing to promote new growth. I firmly believe it is important to maximize all the elements of good growth and nutrition as soon as possible in these situations without inducing stress. This includes allowing the plant to dry slightly before watering, fertilizing on a regular schedule, keeping the soil warm, introducing the plant to increasing light levels as soon as it can tolerate it, and allowing for good air circulation.
There is a careful balance to optimizing these conditions without inducing new stresses, but the reward is to push the plant out of danger by returning it to healthy growth as soon as possible.
This half strength fertilizer myth is pervasive in bonsai books and culture. Even many nurseryman espouse it. I think what is at work here is that people read bonsai books and repeat what they have read and heard without really stopping to think about it, or doing some intelligent research. Put me in this group as well. Even though I have fed my seedlings and cuttings at full strength for years, until recently, I too fertilized at half strength on the advice of bonsai books. Then I started taking a hard look at the results, which were disappointing. I now treat my bonsai as what they are: container plants.
, 40% pine bark falls into the category of "something heavily organic".
