Some reasons not to fertilize:
- Organic fertilizer is a buffet for micro-organisms, both bad and good. After repotting, there are numerous points of entry for bad ones to get in. Some microbes respond with heavy growth if a plant sends out damage related signalling molecules. Both the bad and the good. Whoever ends up on top? We can't be sure.
- Too much fertilizer will kill developing and established roots, no matter if there was a repot or not.
- It's a fact that roots grow less if they're supplied with the right amount of nutrients. Especially nitrogen seems to have this inhibiting effect.
- The way bonsai people dose their nutrients always amazes me; they put little packets of highly concentrated nutrients on certain spots. This can actually kill roots due to overdosing them. I'm sure it has its benefits in established plants, to provide localized growth improvement. But with restorations going on, this could very well be a wrecking ball. We give our kids bacon and pork chops, but we don't try to stuff an entire wild boar down their throats.
- It's hard to dose right, how much is needed for a new container with a different size from the previous? There is no rule to abide to (well, actually there is, but that's some deep science). Especially for beginners, it's hard to estimate the demand for nutrients of a certain plant. If you want to be totally safe, go with the safest option; don't feed until it's back to its original state.
- Nutrients can block the soil from breathing properly and they can cause algal blooms. Algae are bad.
- Plants can keep growing when they're fertilized and give off the vibe that they're entirely healthy, until winter comes and then suddenly die due to a lack of roots.
Some reasons to fertilize:
- The plant needs the building blocks to repair damage, where is it going to get them in a barren soil?
- Switching from a heavily fed soil to a soil that is devoid of nutrients is a GIANT shock to all plants. Why isn't anyone watering consistently with deionized water? It's probably because the water is so empty, it will extract nutrients from the plant. I wouldn't want a shock + another shock. I prefer a steady change of environment; all of my soils are premixed with nutrients. This eliminates at least one shock factor of the two.
- Who needs rapidly grown roots? We need healthy and strong ones, if they take extra time because they're of higher quality, then I'd prefer those.
- Roots, and all other plant parts keep consuming nutrients even when they're damaged. Buy your wife a floral bouquet, and the florist will hand you a pack of light fertilizer for free. If they're not making money off of it, and it doesn't benefit the plant, why would they hand it out to you? What do bouquet buyers know about horticulture? They could have sold you that pack for an extra 5 bucks!
- Even if the roots have limited abilities for a while, they still function albeit in a more relaxed state. The rest of the plant is still high in demand for nutrients. Unless you're taming a beast, you might want to consider feeding it. This is a breaking the cycle versus not breaking the cycle kind of thing.
- We want auxins and other hormones to do their job. Have you ever looked at the chemical composition of indole-3-acetic acid? It needs a nitrogen atom. Where would a plant get that? From the air? Where do those air-nitrogen-capturing bacteria usually live? Right.. In the roots we just cut off..
- We don't want our plants to spend their reserves on both growth and restoration, while they could just be not spending their reserves at all. That's what reserves are for! For those extra extra hard times.
These are the main arguments I could come up with, both sides have very sound reasons and I believe everyone should decide whatever they feel is best. I have never found any negative effects from feeding a repotted plant. I even feed my collected plants.