I would like to share with you my thoughts on the implications of Limiting Factors for tree growth. The basic theory is that the optimum rate of growth of a bonsai will be limited by the one resource that is in the least supply. Obviously different trees require different balance of the essential factors but the basic theory remains. To recap the factors are water, light and the wide range of nutrients.
Leibigs Law “states that plant growth is limited by a single resource at any one time; only after that resource is increased to the point of sufficiency can another resource increase plant growth”*
We need to be mindful of this when choosing soils for re-potting, when watering and fertilising, and when choosing a place for our trees in the garden. For instance a light demanding tree can be well watered and fertilised but without adequate sun to photosynthesize, will always fall behind its own maximum potential.
It is interesting to see how plants respond to a Limiting Factor: “One of the major mechanisms by which plants adjust to resource imbalance is by allocating new biomass to the organs that acquire the most strongly limiting resource”*. This means that they can grow more leaf that root or vice verse – overall making the plant out of the balance that is so critical for quality bonsai.
Consider how a bonsai will respond to our attempts to improve growth with an oversupply of some nutrients without addressing the one that is missing. A plant will ‘spend’ Carbon to acquire Nitrogen and ‘spends’ Nitrogen to acquire Carbon. Essentially the plant can compensate to access the limiting factor, but again the cost is clearly a reduction from its maximum growth potential.
This was reinforced for me recently when I was fortunate enough to listen to an expert in hydroponics (the growing of plants without soil) speak and was very impressed with the results achieved by supplying the exact nutrient requirements of each species of plant (chemical analysis of leaves used to determine what the Limiting Factor was in each case).
One side effect is unexpected: “Individuals within a species tend to increase leaf and root longevity in response to nutrient stress.”* Starving a plant of some nutrients makes them tougher in the long term. I have been experimenting with this by holding back the Spring time feeding regime by a few extra weeks with the result so far showing no difference in tree health, and trees that (anecdotally so far) seem more resilient.
*All quotes taken from: Chapin, Bloom, Field, Waring (1987) Plant Response to Multiple Environmental Factors, Bioscience Vol.37 No.1