Fertilising in grow pots

[Tim K]

I’m new to the forum and new to bonsai in general but I’m eager to get a few of my trees to increase their thickness. Right now I’m going for thickness in grow pots with a plan to cut back to 1/3 desired height once 2/3 truck thickness is achieved which I’ll repeat a few times.

I’ve read about the fertilisation regimes for each of my trees but if I’m going for trunk thickness would it make sense to go for a relatively high nitrogen fertiliser in growing season? Am I right in thinking this would speed up leaf production and therefore trunk thickness? I know the downside is long internodes but surely this won’t matter until I’m developing branches in a couple years...

Am I missing something here?

[Watto]

Hi Tim and welcome to Ausbonsai.
If you could put your location in your profile that will help with any advice that the members may offer.
Go hard and go often if you want quick growth. High in all the NKP's won't hurt and use both solid and liquid fertilizer, maybe all year round (depending on location). There are of course down sides to this but if you want thickness quickly this is the way to go in my opinion.
You can work on the other aspects later.

[Tim K]

Thanks Watto - I’ve updated my location, which is Sydney.

If I’m using a bonsai potting mix that already has slow release NPK and then I fertilise with a high N liquid all year round, could this result in damaging the roots? Or is this negated because bonsai soil is so fast draining?

Surely the answer would depend on the species as well though right? For example - Port Jackson figs seem to like alternating 1/2 strength high N then full strength balanced fertiliser every fortnight vs bald cypress which like balanced every week. If I gave both of these full strength high N (Weekly? Fortnightly?), would that be bad?

[Watto]

Don't try to make it too complicated, go for full strength fortnightly.

[Tim K]

I’m totally down for simplicity. Thank you

[shibui]

I also endorse full strength fertiliser fortnightly for growing trees. Most are able to just take what they need and ignore the rest which is usually flushed out when you water.

[Tim K]

Shibui, would you also suggest higher N for trunk development?

Watto, would you say that fertilising all year round is okay in Sydney for all of these: paperbark, bald cypress, Chinese elm, port Jackson fig, Chinese privet, and juniper procumben

[treeman]

Most are able to just take what they need and ignore the rest which is usually flushed out when you water.

If that was true Neil then there would be no such thing as injury through high salinity or the various toxicities. Also,too much N can be taken up at the expense of root growth and disease resistance. Unfortunately plants cannot ''ignore'' what is in the medium.

[treeman]

I’m totally down for simplicity. Thank you

Then use a controlled release fertilizer like Osmocote or Nutricote at a rate which gives you the amount of N to serve your purposes.

[PWC]

I also endorse full strength fertiliser fortnightly for growing trees. Most are able to just take what they need and ignore the rest which is usually flushed out when you water.

I am using Osmocote Professional potting mix in my grow pots, would you still recommend a 2 weekly feeding regimen with this mix ?

[Tim K]

If anyone is interested, I just found this on another forum:

The last point about thickening is heavy applications of fertilizer will help. Lots of nitrogen, though, tends to produce long internodes, which we want to avoid in our bonsai (because branches and ‘back budding’ generally can only occur at nodes). So one wants to start with a seedling/sapling/trunk that has short internodes, particularly the last internode to be retained; after that one doesn’t care because it will be cut off. Then one wants the next segment to be suitably short – it will help to restrict nitrogen while it is being grown, then again switch to high nitrogen after it is set to thicken. Basically this nutritional manipulation is only possible in containers.

Thoughts?