AusBonsai

So I'm kind of stuck here, I've always use miracle-gro's 24-8-16 instant-release fertilizer at a rate of ~8% nitro (1/3 of a serving) every third day, and maybe every 9th day I'll do a 16% nitro day, I do this to try to keep my substrate's fertilization as homogeneous as possible but was still unhappy with it, still thinking that at day 2 of no fertilizer that the substrate was likely very low (If it's not raining I often water 3x/day during the summer)

I figured an extended-release fertilizer would be a better solution and finally chose one, 'Osmocote Plus', a 15-9-12 with a "6 month release" (have to imagine that this release isn't consistent, that those coated-pellets release far more in their first two months than in months 5 and 6....)

So I've got this stuff now and want to start using it but I don't know how to dose/apply it, the label's smallest usage-prescription is for 2 gallon containers.....not bonsai! They advise a capful (3TBSP) for a 2-gal container, so I can go by that rate for my bigger specimen but I've got tons of containers that are <1/2gal of substrate and guess I'm worried that, if I simply do my best to guesstimate their volume and then apply based on the 3tbsp/2-gallon-substrate rule, that it could be over-doing it (ie, the small containers may not 'buffer' against it very well)

If anybody uses this product or something like it I would love to hear how you apply, like what doses you put down on what size containers (also curious how often you apply, as I'd look at a '6 month release' product and think 3-4mo would be the max I'd rely on it for...) Also, if you're able to tell me what you use, I'd love to know if you consider it low/normal/high as I'm really trying to push a lot of growth (most of my trees are stock/pre-bonsai so just going for branch-girth on a lot of my collection!), my ideal here would be to find the highest appropriate rate of the osmocote and use ~80% of that, and then use the instant-release 24-8-16 as a supplemental based on what's going on ie giving a big dose to a tree that's in the middle of a strong&fast growth-flush!

Thanks for any advice on this one, it's so darn confusing trying to switch-over here because the #'s on the products are based on such incredibly different "availability rates" that I don't know how to compare to the two- for instance, if both were the same NPK%'s, something tells me that using the instant-release at the proscribed rate (every 1-2wks) for 6 months would give WAYYY more fertilization than 1 application of these granules every 6 months - or maybe not, maybe the rapid-drainage of bonsai substrates means I'm throwing-out 95% of my instant-release when I water, and that these timed-release pellets will be more potent because they don't wash-out at remotely the same rate my instant-release dose...ugh so confused here!

[also I should mention that I'll be applying this stuff as a top-dressing for now, with the intent of mixing-into future substrates, but for now I'll just be top-dressing the stuff....with them advising 3TBSP for 2gal of soil, I guess I'd be aiming around 1tbsp for most of my smaller stuff - if anyone's got any 'info-graphics' that show visual fertilizer-overdosing signs I'd love to see it so I can be on top of this, I figure the worst case would be that I use enough osmocote that I don't need / can't use any miracle gro, but am thinking it's smartest to aim for ~75% of the fertilization coming from the timed-release and the rest from instant, roots want a consistent supply of nutrients and w/ how fast bonsai-substrates drain-out I just don't think an instant-release-only regimen is very wise..]

Below is a Scholarly article about release rates. It would appear your thoughts were right in regards to the rate being higher just after application and petering off over time, with all Controlled Release Fertilisers (CRF) having low rates of fertiliser release well before their claimed release periods.

I, and others, use CRF's in the mix as a background supply and then use liquid or slow release (pelletised chook poo, etc(which aren't very slow as most fert gets dumped within a few waters)). If you read the below article you will also see that temperature has a big effect on CRF's, with an increase from 30 deg Celsius to 40 deg Celsius meaning an even shorted period of release. So if you water heavily in summer you will probably release any CRF quite quickly.

https://www.tandfonline.com/doi/abs/10. ... 0009370490

I'm exceptionally lazy; in non-sensitive plants like my Elms and Maples i just mix through a rough 1/4 cup of osmocote/ similar and blood and bone into a couple of spade fulls of potting media, then liquid or pellet feed if necessary (usually very infrequently with maples so i don't get long inter-nodes). My theory being that the trees are getting some nutrients over time without having to overload them and get coarse growth. Then i adjust my liquid or pellet applications on how they are progressing through the growing season.Thus far (4-5 years) it seems to work through i don't really push my trees hard.

You are over thinking it. Fertilizer companies want you to use as much of their product as possible. That is a given. If they have determined the max rate for top dressing is 3 spoons/2 gallons of mix and you want to push growth then use that rate. Just be aware that released concentration will increase as the temperature does. If you have continuous hot whether you will need to keep the substrate moist to wet at all times or the EC could increase too much. Alternatively you could reduce the rate by 25 to 33% to account for the pots drying. For greater control, use the lower rate and supplement with liquid as you see fit.

Maybe fertiliser companies want us to use plenty of the product but I believe they are also wary of overdose so I think application rates are generally a bit conservative to allow for heavy handed consumers.
I use osmocote exact Lo start 16-18 month 15-8-11 +2MgO + TE (only available in 15kg bags) in the mix when potting up. Scotts promote this one as 3rd generation. Not only is it slow release but also is patterned release to suit plant growth. Initial release is slow but gradually increases with time. I figure that should match my tree fert demands - little initially but gradually more as the plant starts to get active and grow larger. If you believe the company propaganda 2nd and 3rd generation product are designed to not dump the contents in warm weather so should release gradually whenever there is moisture. There is still some increased release at higher temperatures but that is when the plants probably need it more. Release at 26C is 12-14months - no figures supplied for 30C-40C summer temps??
I use a conservative rate, about 2/3 of recommended, and supplement fert with liquid at 2-3 weekly intervals. The aim being to have the osmocote provide a constant background supply whether I remember to fertilise or not. The soluble supplementary fertiliser provides extra and can also be varied to allow for seasonal changes like flowering species in autumn.

I have read company advice that the best way to apply is into dibbled holes in the mix. 2nd preference is mixed with the potting mix and least desirable is spread on top. Rather than top dressing with osmocote I would try drilling holes and dribbling the required amount into 3-6 holes per pot. I often drill holes with my shears or scissors (push closed tool down vertical then rotate the tool to open up a hole the diameter of the blades) but a sharp stick should also work. Just needs to be large enough to dribble the prills into.
I have not been very precise when drilling extra osmocote into pots after the second year and have never seen signs of overdose.
I second Treeman's advice - stop overthinking and try it out. Many of us use controlled release with bonsai without any problems.

dansai wrote:Below is a Scholarly article about release rates. It would appear your thoughts were right in regards to the rate being higher just after application and petering off over time, with all Controlled Release Fertilisers (CRF) having low rates of fertiliser release well before their claimed release periods.

I, and others, use CRF's in the mix as a background supply and then use liquid or slow release (pelletised chook poo, etc(which aren't very slow as most fert gets dumped within a few waters)). If you read the below article you will also see that temperature has a big effect on CRF's, with an increase from 30 deg Celsius to 40 deg Celsius meaning an even shorted period of release. So if you water heavily in summer you will probably release any CRF quite quickly.

https://www.tandfonline.com/doi/abs/10. ... 0009370490

Damnit! Thanks for that, was afraid that'd be the case....people are just so damn greedy! When I used to manage a vitamin/supplement franchise, one day we thought it'd be fun to test the timed-releases of certain pills, the results were downright scary (some were fully dissolved within 10min, others were still solid 48hrs after the fact, etc...we'd gone online and found the right amount of vinegar to use in the water to approximate the human stomach so it's not like it was just in water.... anyways the release-rates were just all over the board, zero correlations could be made on anything, led to the conclusion that 'timed release' can mean anything from extra hours to...forever? lol!

I've been doing as you mention (using both), how do you split your total-fertilizer-input between timed-release and instant-release? I've currently been aiming to apply ~50% of my fertilizer via my timed-release osmocote-plus (15-9-12) and 50% via instant-release miracle-gro (24-8-16, and when doing instant-release I'm adding my micro's-mix, and sometimes magnesium or iron), have also had to up the phosphorous load due to using a pH-Down product (phosphoric acid), if my rainbarrel reservoirs run dry (150gal goes faster than I would've ever guessed! ~100 trees would do that I guess!) then I have to use that stuff to bring-down my 8pH tap-water and I know that's just adding a ton of phosphate I wish I knew how to calculate it :/