I tend to listen carefully to advice offered by others, especially when the advice comes from people who have proved by their achievements that they know (or should know) what they're talking about. In the fuchsia world there is no shortage of such advice, including many 'golden rules' that have been passed on from expert to expert from time immemorial. I have to confess that there are one or two of these golden rules about which I have my doubts.
Take for instance the rule about potting on. "You should pot on in one inch increments", so it goes - that is, from a 3" pot to a 4", from a 4" to a 5", and so on. The advice is given in old fuchsia books, and in modern ones too. You will find it in magazine articles, and speakers at our monthly meetings will tell us to do it as well. Everybody says so.
The reasons given for this practice seem, on the face of it, to make some sense. I have come across three. The first suggests that by such practice we encourage the plant to develop a compact root system that makes use of all the room and compost available to it. Here I am not at all sure that the development of a root system in soil-based compost in a clay pot that is porous to air and moisture is necessarily the same as that in peat-based compost in an impervious plastic pot. But let's put that point aside for the time being. The other two reasons are that it is not good practice to give the plant access to too great a quantity of compost that might grow stale or have its fertiliser leached out of it before the roots reach it. There is also the risk that a large excess of compost might get (and remain) waterlogged - an adverse condition that could affect the whole of the pot.
Recently I have been doing some calculations on the volumes of compost in various size pots, taking into account the small space we leave between the top of the compost and the top of the pot to allow for watering. The results are given in the table below. They are approximate because of the small variations between one manufacturer and another.
If we look at the increase in the amount of compost we make available to the plant as we pot up from one size of pot to the next, the one-inch rule appears to be satisfactory. As the plant gets bigger, the extra volume of compost given to it by potting on gets bigger too - no problem! But if we look at the increment as a percentage increase over the previous root volume a rather different picture emerges. Here we find that the percentage increase from one pot size to the next gets progressively smaller as the pot sizes get bigger. Thus in potting on from a 2" pot to a 3" pot we give the root system over 200% extra compost (i.e. over twice as much) whereas by potting on from 5" to 6" we provide an extra volume of compost of only 59% (i.e. just over half as much).
Bearing in mind that most of our potting on from 2" to 3" is done in the early part of the year when plant growth is slow, and that we pot on from the larger sizes later on when root growth and foliage area are much greater, the 1" potting on rule seems scarcely to meet its objectives - quite the opposite, in fact.
Personally, I usually keep to the 1" potting rule up to the 4" size, but after that - providing the plant is growing vigorously - I jump to a 6" pot (other times I go from a 3" pot to a 5"). Then, if I want the plant to go into a larger pot, I go straight to a 7", 8" or even a 10" size. In other words, my 1" rule quickly becomes a 2+" rule. So far I've never experienced any adverse effects from this practice. As far as I'm concerned the slavish adoption of the one-inch potting on rule is a bit potty. But then, someone out there might like to try to shoot me down.
I suppose it's all a matter of common sense really. As my old grandmother used to say, "everything in moderation". Just about the three wisest words I ever heard, I think - albeit a bit boring.
