Fertilizer question...

I have liquid and granular fertilizers that I use during the growing season depending on the plant/situation, but many times I lose track of when was the last time I fertilized or when it's time to fertilize again.

I was reading the other day about how helpful/convenient, and even better, slow-release fertilizer can be for plants, particularly potted plants, and potted plants in the greenhouse.

I bought a big of Osmocote.



It has an excellent rating on Amazon of 4.7/5 stars over almost 20,000 ratings.

The company states:
*Osmocote is the original slow-release plant food. Decades of rigorous field testing confirm product effectiveness with hundreds of plant species in a variety of climate and soil conditions.
*Each homogeneous granule contains 15-9-12 NPK plus micro and secondary nutrients and feeds up to 6 full months.
*Soil temperature controls how Osmocote releases its nutrients, and more importantly how nutrients are taken up by the plant. Replenishment and feeding are in natural harmony.
*Even if over-applied up to 3x the recommended rate, Osmocote does not 'burn' the plant.



I am looking forward to trying this fertilizer.

Has anyone out there ever used it or use it now? What do you think of it?

Wonderful 'lazy gardener' product. Use it once in the Spring and forget about feeding until next year, at least where you are. It's great for potted plants especially.

I like timed-release fertilizer, but there are much better options than old Osmocote.
Because of the way different elements and compounds move out of a single coating, a portion of the fertilizer will not leave and never becomes available to plants. Better pelleted timed release foods have several differing coatings each customized for a different group of elements.
Nutricote used to be good, but I think it's changed (and not for the better); another good one was the Pro version of Osmocote, but I don't think it's available in small quantities. The ones I have used for many years are made by Simplot - branded as Apex. They may not be available in small quantities either, but they keep well. You might go in with a neighbor and devide a big bag.

I use Osmocote in all of my planters every summer. I mix some in when I plant them in spring along with some earthworm castings, mid-May to June 1st. When planters are watered daily though, none of the time released fertilizers work as long as they claim (note the words "feeds up to 6 months"), so I usually give them all a 2nd dose of both Osmocote and earthworm castings by late-July.

I also feed the planters daily through the drip system on a low dose of a cocktail of fertilizers I found out about at Pesche's (Miracle Gro, SuperThrive and Monty's PlantVantage), and this gives me the healthiest plants with a ton of flowers that last well into fall. I grow a lot of flowers that are heavy feeders, like petunias.

But I like Osmocote and will continue using it, it works out very well for me. I've never had it burn or harm plants at all, it's very safe and reliable to use.

I use it. When I repot my plants in Spring, I top dress with it. A lot of the plants I grow are very heavy feeders. So I have the Osmocote, then intermittently, I also feed with water soluble fertilizer.
For palms, I scatter a dedicated Palm fertilizer instead of Osmocote.
For most of the orchids, I use Dyna Grow BLOOM

I use this product in my flower beds, in the soil where and when the annuals are planted each year, and also top dressed and scratched into the surface soil around the perennials. I have been pleased with the results, and how easy and convenient it is to use. Also great for my container plants.
As in all fertilizer, pesticide, fungicide, etc. products, always follow the directions to the letter, and read the entire label for optimal results.

Glad you posted it I was looking into for my tomatoes and peppers seedlings for indoors until they can go outside I find that the tomato tone type stuff causes to much mold in my soil .

Its important to know the difference between Osmocote and Nutricote (aka Dynamite) slow release fertilizers. It may help you decide which one to use.

Osmocote is a controlled release. What 'controls' it is the temperature of the soil. It needs to be around 80F to start releasing, and it does it because molecules in the little balls expand at that temp, and when water hits them, they release. If the soil temp is below about 80F, Osmocote will not release. It just sits there. That makes Osmocote my choice, because I don't actually WANT all my plants to be getting a hit of nutrients in the cold months.

Nutricote (Dynamite) is a chemical release, not a controlled release. It isn't dependent on the temp of the soil. Whenever water hits it, it will release. SO every time you water its releasing a bit.

That makes Osmocote more cost effective for me, because its not releasing in the winter and getting used up when I don't want it to be releasing.

Gina1960 said: Its important to know the difference between Osmocote and Nutricote (aka Dynamite) slow release fertilizers. It may help you decide which one to use.

Osmocote is a controlled release. What 'controls' it is the temperature of the soil. It needs to be around 80F to start releasing, and it does it because molecules in the little balls expand at that temp, and when water hits them, they release. If the soil temp is below about 80F, Osmocote will not release. It just sits there. That makes Osmocote my choice, because I don't actually WANT all my plants to be getting a hit of nutrients in the cold months.

Nutricote (Dynamite) is a chemical release, not a controlled release. It isn't dependent on the temp of the soil. Whenever water hits it, it will release. SO every time you water its releasing a bit.

That makes Osmocote more cost effective for me, because its not releasing in the winter and getting used up when I don't want it to be releasing.

Thanks for that explanation, Gina. I use Pro Mix Organic Seed Starter. I don't plan to use the Osmocote until I up-pot which won't be for at least 6 weeks. I only plan to use the Osmocote on these up-potted plants that will be staying in the greenhouse. By then, 80 degrees is not problem. Even sunny days now, 80 is no problem in the greenhouse.

Cloudy, cold days like today, 44 degrees and winds in the teens, my greenhouse is at 71 right now. This new greenhouse holds the heat so much better than the old one, especially with the pond, brick floor, and Phase Change Panels.

Keep in mind the ambient air temp does not affect the release of Osmocote, only the soil temp

Gina1960 said: Keep in mind the ambient air temp does not affect the release of Osmocote, only the soil temp

Right. Thanks.

Great explanation Gina.

I wonder if watered with cold water will it prevent the release. Or conversely with a warm temp water aid the release. Probably not but my mind ventures in different directions

Gina1960 said: Osmocote is a controlled release. What 'controls' it is the temperature of the soil. It needs to be around 80F to start releasing, and it does it because molecules in the little balls expand at that temp, and when water hits them, they release. If the soil temp is below about 80F, Osmocote will not release.

Not true. I use this product with good results and our soil temperature is almost never above 80F for long.

The release goes up with temperature (so it will be faster at higher temps) but it is still quite significant at temps below 70F (which is the case for all soil here except the topmost layer, for almost all of the year).

I am going on what the literature says. That's all I go on. I don't watch the little balls dissolve to see what temps they dissolve at LOL. I do know that the hotter it is, the faster they get used up. SO you may not get the full time they promise between fertilizer applications in a hot climate like mine

Every planting hole in the Garden-
Every pot- (almost)
For many years.

Springtime-
For established potted plants, if I'm lazy, I throw it in the top of the pot and mix the soil up lightly or top-dress afterward with a bit of fresh soil. If I'm in a more dedicated mood, I'll poke several holes with a stick or dowel down to mid-pot (root) level, drop some in and cover them.

For the front porch display pots- I use a measured dose of osmocote and water absorbing crystals together in the root zone when planting. They are in the scorching afternoon heat all summer long!

For up-potting seedlings, I don't mix it into the potting mix in a bucket, I carefully count and drop a few into each cell around the roots as I plant each seedling so I know all the cells get the same amount.

I still use liquid fertilizer during the year as well, but less with osmocote in the soil.

I do wish the coating was biodegradable- but I think they are working on that.

And the video of how it works....
https://youtu.be/nSduKQQ9fGs?f...

And the osmocote international company website
https://icl-growingsolutions.c...

The mall here has professional landscaping of course and they do what you do. Every year when they replant stuff they put Osmocote in the bottom of the planting holes.

Hi Jim, @Moonshadow

The NPK content of 15-9-12 in this Osmocote Plus 6-month release is probably OK for outdoor potted plants for the summer.

I wouldn't use it in my garden.

Outdoors in soil, and indoors in permanent pots, I would expect an eventual buildup of phosphorus (P). This can stunt plant growth.

A ratio of 3:1:2 N:P:K has been found generally suitable for most types of plants. The original 18:6:12 Osmocote was an appropriate ratio. The 15-9-12 would be better if 15-5-8 but *only* if the soil lacked phosphorus.

If a soil needs fertilizer the ratio is not as important as the rate. The more that's applied of this that's applied, the more phosphorus that's being added that might not get used. Excess nitrogen and potassium are more likely to runoff or to seep deep into the soil. Phosphorus is often called "immobile" because it doesn't seep down rapidly. It resists dissolving.

In general, phosphorus should not be applied to outdoor soils without a soil test. Phosphorus has been removed from most lawn fertilizers now because of repeated applications causing buildup. This has contributed to pollution caused by phosphorus runoff.

There are many different formulations and programmed release rates of both Nutricote and Osmocote. It's not possible to talk about most differences between them without specifying the exact product.

One noticeable difference - Nutricote does not have a plastic prill encasing it. No little round balls left in the soil.

Gina @Gina1960, The plastic prills may be why the mall gardeners put the Osmocote in the bottom of the holes- to avoid having little balls on the surface that children or animals might pick up. Usually they are placed on top for the dissolving fertilizer to sink to the roots, or mixed in the soil for root contact.

When similar products are compared, Nutricote tends to be released more slowly and more linearly in response to temperature than Osmocote. Nutricote's release is not just controlled by moisture though. I've posted an article below about release rates including 13-13-13 (and 2 other) products of each. I use a Nutricote 18-6-12 with minor elements on potted plants in soilless potting mixes.

In my garden, last year I started using the new Scotts Ultrafeed 44-0-5 NPK 6-month release. It has one of the most linear release rates in relation to temperature that I've seen. It's a mix of white and aqua uniform pellets. Easy to see while applying. They dissolve completely with no sign after a rain.

Is it "high" in Nitrogen at 44%? Yes. That just means I'm getting more for my money given the slow feeding rate. Most of the growth response of plants in average fertile silt-clay-loam soils is to added nitrogen rather than the other elements. Remember that how "high" it is actually depends on how much you apply - the rate. It takes some calculating to get to the rate you want.

My calculations came to 2 tsp Ultrafeed per square foot to supply 150 lbs N/acre. That's comparable to rates applied to lawns. It works well for daylilies. I use 1 tablespoon per clump up to about 2 feet across. 1 tsp for new plants sprinkled over a 1' circle around the plant. At the current price of $35/20 lbs at Home Depot, I calculated $0.11 per tablespoon. But TBH most of our 2000+ daylilies don't get fertilized at all and grow very well without it.

Pat

https://www.researchgate.net/f...

Edit: I just realized that these graphs only show the release rates at a single temperature. The study was conducted in a lab at a "constant 23°C", which is 73-74°F. Soil temperatures could be either lower or higher than that.

Very thought-provoking information about chemical fertilizers. Thanks everyone for sharing your ideas and insight as well as your experience using different types of slow-release pellets. You have given me more options to consider!

Hortaholic said: Phosphorus has been removed from most lawn fertilizers now because of repeated applications causing buildup.

Only where we live. Most states in the US still allow it in lawn fertilizers. It's largely an upper midwest thing to ban or at least severely limit phosphorus in lawn fertilizers. A lot of that's driven by Great Lakes health. We have a more direct relationship to the effects of fertilizer runoff. It's a great idea to voluntarily limit phosphorus other places even if the effects are far removed, like in the Gulf of Mexico. Not spending money on spreading something that's not needed because of decades of overfertilization is an added benefit. For most of the US it's voluntary, though.

Great post aside from that quibble.