Osmocote extended release fertiliser granules

[orchidsarefun]

Anyone using this ?
I switched from water based mixes as sprinkling a few granules every 6 months on the surface of the pot is a lot easier, more convenient, cheaper and less wasteful. Formula is 15-9-12 with added minerals. I've even starting mixing into the potting mix when repotting. Any comments?

[PaphMadMan]

Any means to get your orchids a little fertilizer, including micronutrients, that you can do consistently is good. Osmocote is a good product with a long history. I think that formula supplies no calcium, and if your water doesn't supply it that might the only thing missing that could ever be a problem.

Osmocote granules might wash out of coarse bark media, but if your mix is fine enough to retain it that is not a problem. Like any fertilizer, for orchids use it at less than the suggested rate, probably 1/4 of what the label says, and don't apply it in late fall or winter if your plants aren't in active growth.

Many people make a much bigger deal out of fertilizer than is necessary. With what you are doing fertilizer will almost certainly never be the limiting factor in your success with orchids, and no fertilizer can make up for what is lacking in other conditions and care.

[orchidsarefun]

I sprinkle about a teaspoon of bone meal and the same of blood meal when the plants go outdoors once a year. With our municipal water and rain....and osmocote, I think I have covered all bases, probably overkill. All my mixes, whether fine to large bark and terrestrial mixes, contain sphagnum and that probably absorbs and releases fertiliser nutrients when in liquid form.
I do believe that people overworry on fertiliser. Many growers I have spoken to only fertilise roughly 1x per month and never in Winter.

[jcec1]

I use them in my Catasetum types, since they are gross feeders, this is in addition to regular feeding every two weeks. Hard to say if they have an effect as I don't have a large amount of plants and a control. But, certainly no ill effects.

[katrina]

I've used osmocote in the past...no problems. I switched to dynamite (red pkg) a few years back because it is suppose to be good for 9 months...now using the purple package dynamite because it has some added calcium and other micros and I could get it in a big bag on AMZ.

I'm lazy with fert in the winter so I've been putting in the pots when they come back inside. At least 3 yrs now...maybe longer. Been using granular with ctsm for several years and getting good results. I know some people talk about root burn with granulars and orchids but I've never had a problem.

[Ray]

The lifespans and outputs of such products are temperature controlled, so in addition the the formula, knowing the duration@temperature relationship is important.

While we seem in agreement that nutrition is way down the priority list, you don't want to overdo it by using too much of a "6 months @ 65F" product, when your growing conditions average 80 over the summer.

[nogreenthumbs]

I used some as advised by someone that sold me an orchid. I think I ended up over-fertilizing. I'm sure it can be done in a way that is ok, maybe a very tiny amount (a pinch of granules), but for now, I'll stick with my water soluble fert.

[orchidsarefun]

Originally Posted by Ray

The lifespans and outputs of such products are temperature controlled, so in addition the the formula, knowing the duration@temperature relationship is important.

While we seem in agreement that nutrition is way down the priority list, you don't want to overdo it by using too much of a "6 months @ 65F" product, when your growing conditions average 80 over the summer.

Agree. It seems Osmocote longevity is tested at 21c/70f and if that is an average, then most cooler growers will obtain maximum advantage. I don't know if water temperature also plays a role but I doubt rainwater is consistently higher than 70f ( at least where I am) and my tap water is probably lower. They claim that plant burn is impossible - that I can soon confirm. Osmocote Plus supposedly has 6 month longevity. More than enough for my 3-4 month outdoor growing. Indoors temps are consistently around 70f.
The fertiliser was developed with the billion $ nursery industry in mind. There are lots of scientific articles on the internet and it's evident that the time release coating has been consistently improved - if unnecessary wastage ratio is improved, $ benefits accrue.

About Osmocote Controlled Release Fertilizer - Fertilizers - Fertilizer supply companies - Wholesale Nurseries Suppliers - plant nutrition

[Ray]

As I said earlier, the longevity is not the only factor to consider. A 6-months product @ 70F when used at 80F, will have a shorter longevity because it is dumping its contents faster, increasing the concentration in the medium.

Beside the issue of it washing out of a coarse, open medium (resolved by making a pouch of it from old panty hose, and placing it above the pot, so it will fertilize at every watering), I'm just not sure how much to use.

If I start by assuming my temperature is exactly 70 degrees all the time, so the longevity is 6 months, and also assume (inaccurately) that the "dump" is uniform throughout that time period, then what we have to do is equate a "3x/week @ 25 ppm N" to a "26 weeks" application, right? Wrong.

Sure, we can probably safely assume that a single dose equal to 3 x 25 x 26 = 1950 ppm N is the way to go, but how does that relate to the volume or weight of the pellets? Ppm is a concentration ratio, not fixed mass.

Do I merely adjust for the volume of each pot? Probably not.

What is the retention rate of your potting medium? I.e., how much of that 25 ppm N solution stays in the pot when you water? A much greater percentage of the ooze from the Osmocote does, right?

All that uncertainly has prevented me from ever using it on my orchids. Turf and shrubs? No problem, as the manufacturers know what they're talking about with their recommendations. Orchids? Sorry, they don't know diddly about that.

I may not think fertilization is critical, but that doesn't mean I don't want to control it.

[nogreenthumbs]

It seems like I've read somewhere (who knows how accurate) that the initial dump is a small spike that then slows to the normal slow rate for extended release type fertilizers.