Osmocote Topdress product for container grown blueberries

I would like to ask a couple of questions with regard to slow release fertilizers:

  • What do you think what is the best (most convenient) NPK ratio for young blueberry plants grown in containers with peat moss/cocopeat/pine bark/perlite mix.
  • What is your opinion about the product given below and its composition with regard to blueberries. Its longevity is 4-5 months.
  • What would you suggest what I need to do for compensating for missing Ca.
  • I have read that it is not recommended to fertilize newly planted seedlings and it could be done in mid-summer or a month later. do you agree?
  • How about recommended doses for a 30 lt (8 gal.) container? 10 gr?SS2190
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not really sure about osmocote but i got some advice from @fruitnut about 7 years ago in regards to fertilizing bb’s and still do it that way. I use Ammonium Sulfate at a rate of 1 Tbls. per 3 gal of water and i saturate the plants once a week through the summer maker sure to stop ferting in august so the plants stop growing and can harden off for winter. results for me have been phenomenal.


Thank you for the information… I guess yours are in-ground grown BBs right?

The fertilizer has too many nitrates, i would not use it. If you want a slow release use Holly-Tone organic. I use it once a month starting in April. I also supplement with a soluble for acid loving plants. I use both together, soluble and organic. the soluble works for the first 2 weeks and by the time it fades away the bacteria have broken down the organic. Works fine in containers too. I grow both in ground and containers. I would not worry about the calcium. The sulfur in Hollytone with bacteria will breakdown to sulfuric acid. The acid will react with any carbonates and form gypsum, which is a source of calcium for the plants. Keep an eye on pH. I would not use Ammonium sulfate in a container grown plant. It’s too easy to make pH too low. Use a urea based soluble like Miracle grow for acid loving plants or Mir-acid. It’s OK to use AS a couple times a year on containers, but monitor pH I stopped using it as it often clumps and becomes very hard. Now instead I use Jack’s acid fertilizer which has AS but also has PK and the needed trace minerals.
It’s much more expensive, but convenient and does not turn to rocks!


Drew has makes a good point. Here’s a bit more detail.

The blueberries evolved where there was minimal NO3- in the soil. Nitrates are not used well by blueberries since they have very limited nitrate reductase which converts nitrate into amino acid which is used to build proteins


Blueberry Council of Missouri - AgEBB - University of Missouri

](Blueberry Council of Missouri)

If you click the link you will get a very detailed explanation. Nitrate is often claimed to be harmful to BB’s, I’m not sure about the research on this but I wouldn’t use it on BB’s.

Too bad, because Osmocote is an excellent container fertilizer for most plants and greatly simplifies the process because of its encapsulated form of timed release, much better system for containers than Hollytone, I would think, but if Drew has success with it, I really can’t say. I don’t grow BB’s in containers, but Osmocote works much better for me than other types of fertilizers for the things I do grow in containers.

If you can find a form of resin encapsulated fertilizer better suited for BB’s (no nitrates) I would highly recommend it.

Someone who used to participate in this forum was growing blueberries commercially and used a similar product from a company with flori in the name and got outstanding results. I think he was starting his plants in containers with it.

Here it is- Florikan. You can call this source and find out if they or Osmocote make one with only coated urea. https://www.amleo.com/Search.aspx?ss=fertilizers

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I think Fruitnut said he used Osmocote on blueberries. But it may have been ”Osmocote for acid loving plants “ or some such. They slice and dice the market every which way.

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Osmocote was the original company that developed polymer coated N. Their product used to be the best but that was a while ago.

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Thank you Drew for detailed information:+1:

Thank you Alan for NO3 warning…:+1:

i use the ammonium sulfate for potted and in ground bb’s.

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Ammonium Sulfate can be dissolved in warm water first,before applying it to the plants.bb

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Such a product exists, but after the terrible review of it by Steve aka frutinut, I don’t even mention it anymore.

I used to but my soil in containers is such a low pH and the AS lowered it even more, and I lost 2 plants. The pH was below 3.5. Not like I used too much. I used 1 teaspoon for 2.5 gallons, but that was plenty to kill them. It may depend on your potting mix, mine was only pine and peat, nothing else. both have a pH of 5.0. So I’m gun shy of using it. I view it as crack for blueberries. I prefer other approaches. It was my bad for not keeping an eye on the pH. I could have avoided it.

Yes it should be but hard to measure amounts when you have a brick of it. I just don’t like the product. It works great, but it killed two of my plants, and I don’t want to have to constantly monitor pH. I check at the start of the year to see where I’m at. I never ever put it on directly. I always diluted it first and it would be very wise to do so.

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Oh,it clumps together in the bag? I’ll have to check mine.Probably absorbs some moisture?
I’ve been using the Jack’s too,what they call professional,at 21-7-7,a little more N than their Classic Acid Special,which is 17-6-6,the one I first used.bb

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I think that s a more reasonable one… But I would like to hereby to Steven (FruitNut) about the drawbacks Drew mentioned above?

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Yes it does seem to pull moisture out of the air. If one kept it well sealed, but I’m not a neat person, it doesn’t fit my lackadaisical approach. My wife will not let me fold clothes! The folds are not neat enough for her! I suck at being neat! So I left the bag open by not paying much attention. It’s just me! Nothing wrong with the product.
The Jacks seem not to clump, plus it’s a complete fertilizer not just nitrogen.

I’m so looking forward to berries, my plants all look awesome and it’s going to be a very good year.

I like using Jacks on my in ground as they have some compost which raises pH besides the bottom being in contact with the native soil. It’s just about impossible to lower pH too much with those in ground plants.


Good pro-tip right here. I need to check how my bag is doing and maybe double-bag it or split off some into a freezer zip-top bag.

Your wife would hate my technique then. First, I leave it in the clean laundry hamper or even in the dryer until its nice an wrinkled. Then I put it away by folding shirts just in half once, same with pants. Socks and underwear don’t get any special treatment either, just get tossed right in the bottom drawer to be sorted through when I need them. To get rid of the wrinkles for shirts and pants when I need to wear them I have a spray bottle and just spray it with a small amount of water and shake it out, works almost instantly and dries in a couple minutes.


I’m not growing blueberries right now. They are difficult here with everything alkaline. The advice above sounds good to me.


Yes she is crazy neat, just look at my t-shirt drawer, stored vertical so i can see them all! I messed it up a little getting one out :slight_smile:


It is very helpful with BB’s to know the pH of your water as that is why one may need to continuingly dose the fertilizer with strong acidification- to compensate for the alkalinity of your water. There is no need to constantly add sulfur if you aren’t constantly driving pH up with your water. A soil mix out of peat-moss and sand usually creates a suitable pH for BB’s .

If you collect rainwater from you gutters that can solve the problem- as long as the rain keeps coming or you have adequate storage.


I can go to the site where I am experimenting only once a week. For the time being I adjust the well water ph with citric acid down to 5.5 each time I irrigate. In the following weeks i will try to set up an automatic system for that. The EC of the water is 0.350 . I have heard it would have been better if it was below 0.2 but still this would be tolerable. The substrate ph is around 4.75.

If I can feed them with slow release fertilizers, I will not need to add liquid fertilizers to the water, that is what I am aiming at. I think as long as the fertilizer is mostly urea based, I guess there will be no ph problem… Right?